Absorption
The penetration of a substance, eg. gas or thin film
of liquid, into the surface layer of a solid with which it is in contact eg. process by which herbicides are taken into plant
tissues by roots or foliage (stomata, cuticle, etc.).
Acid equivalent
The total organic acid content of a substance expressed in terms of the active
acid. In herbicide concentrates, it is the content of active ingredient
expressed as a free acid.
Active ingredient (a.i.)
Toxic component of a formulated herbicide.
Active site
The portion of an enzyme which specifically combines with the substrate.
ACCase
acetyl-Coenzyme A carboxylase; enzyme
responsible for production of fatty acids and is the target of many herbicides
that have the lipid synthesis inhibitor mode of action.
Active Site
The location on an enzyme (protein) to which substrate molecules bind
and are converted to their products. The shape of this site must be maintained
for the enzyme to remain functional.
Additive
Adjuvant; any of several categories of compounds that can be added to a
herbicide solution to enhance its activity. Some examples are oils, surfactants and fertilizers.
Additive resistance
Resistance governed by more than one gene, each of which can be expressed
independently, but which is reinforced by the expression of each of the
additional genes.
Adjuvant
An additive. Any of several
categories of compounds that can be added to a herbicide solution to enhance
its activity; some examples are oils, surfactants and fertilizers.
Adsorb
To gather on a surface (opposed to absorb).
Adsorption
The process of a substance binding to a surface.
Agricultural chemical
A broad term used to cover pesticides, adjuvants,
conditioning agents and other chemical tools used in improving agricultural
production, protecting crops or controlling pests, diseases and physiological
conditions of crop plants. It does not normally include fertilisers.
Allele
One of the different forms of a gene (or marker) that can exist at a
single locus. A single allele for each locus is inherited separately from each
parent.
Allelic
An allele is one of a pair or series of forms of a gene possible. An
example of allelic variation would be a dominant vs recessive allele for one gene.
Allelopathy
Influence of plants upon each other, through the release of products of
metabolism that inhibit the growth of adjacent plants.
ALS-AHAS
Acetolactate synthase or acetohydroxy acid synthase;
an enzyme essential for amino acid production and is the target of many
herbicides including the imidazolinones and sulfonylureas; this enzyme has mutated in some species to
become herbicide resistant
Amine
A class of compound derived from ammonia by replacing the hydrogen molecules
with organic radicals. A form in which some types of weed-killers may be
prepared, notably MCPA, 2,4-D, 2,4,5-T, CMPP and 2,4-DP. These weed-killers
when prepared as amine salts are soluble in water.
Amino Acid
The basic building blocks of proteins. The sequence of amino acids is a
protein and protein function are determined by the genetic code. It is an
organic molecule containing a carboxyl group and an amino group. There are many
in existence but only 20 are common to the proteins of living organisms.
Amino Acid Synthesis Inhibitors
A mode of action of herbicides that inhibit the production of essential
amino acids.
Anionic surfactant
Salt of an organic acid, the structure of which determines surface activity.
Annuals
Plants that complete their life-cycle in one year.
Antagonism
Reduced activity of one or more herbicides when applied together
compared to applying them individually
Anther
The portion of the flower stamen bearing the pollen grains. When the anthers are ripe they open to release the pollen.
Apical meristem
The tip of a growing plant root or shoot composed of cells from which
subsequent growth develops.
Apomixis
Reproduction which has the superficial appearance of ordinary sexual cycle but
actually occurs without fertilisation and/or meiosis
hence, the offspring are generally identical to the mother. Usually taken to
include parthogenesis.
Apoplastic Path
Water moves in the cell wall or non-living region between cells without
crossing any membranes. Apoplastic means 'non-living'
tissue.
Application
The act of administering herbicides. For herbicides, the following categories:
Post-emergence - application of a herbicide after the crop has emerged from the
soil; Pre-emergence - application of a herbicide after the crop has been sown
or planted but before it has emerged; the term pre-emergence sometimes refers
to the weed and it then implies an application of a herbicide before the weeds
have come through; Pre-planting - application of a herbicide before the crop is
sown or planted; Spot - application made to patches of weed.
Application rate
The total amount of herbicide applied per unit area.
Aromatics
Chemicals characterised by the presence of one or
more benzene (C6H6) rings - a large class of cyclic organic solvents, many of
which are odorous. Examples include phenylalanine, tyrosine and tryptophan.
Assimilate
Products of photosynthesis that are moved in the plant.
ATP
Adenosine triphosphate is a substance present in all
living organisms. Its conversion to di- or
mono-phosphate liberates energy used for many organic functions including
muscular contraction, respiration and 'nitrogen fixation'.
Auxin
Indole-3-acetic acid (IAA); the first plant hormone discovered; a plant
hormone involved in many plant growth processes including embryo development,
root and flower development, vascular differentiation, stem elongation, apical
dominance and tropic response.
Auxin-Binding Protein (ABP)
A 22 kDa protein located in the endoplasmic
reticulum which is thought to recognize auxin and act
as a receptor at the cell surface.
Auxinic Herbicide
The first selective organic herbicides developed. This family of
herbicides is described as synthetic auxins, growth
regulators with herbicidal action, or herbicides with growth regulatory
activity.
Awn
Slender bristle-like projection arising from the back or tip of the glumes and
lemmas in some grasses.
Axillary bud
A bud formed in the upper angle between a twig or a petiole and the stem.
Axis
The main stem of a flower or panicle.
Backcross
Crossing (mating) 'offspring' (a hybrid) with its parent to reinforce or
increase the gene frequency of a desired characteristic.
An application of either sprays or granules to a continuous restricted
area such as a band of soil in row-crops, usually in or along plant rows.
Basipetally
Successively from apex to base.
Benzoic Acids
Family of herbicides that have activity on synthetic auxins belonging to the growth regulators mode of action.
Biennials
Plants completing their life-cycle within two years. The first year it produces
leaves and stores food while the second year it produces fruit and seeds.
Bioassay
Determination of chemical effects in tests on plants.
Biological assay
Measurement of the potency of any stimulus, physical, chemical or biological by
means of the reactions which it produces in living matter.
Biological control
The regulation of plant and animal numbers by natural enemies. It is the aim of
biological control to manipulate natural enemies (parasitoids, predators,
pathogens) in an attempt to reduce the pest numbers and keep them at much
reduced levels. The 'manipulation' can involve the introduction of natural
enemies into a region where they previously did not exist to counter
accidentally introduced pests of crops (classical biological control). Also
manipulation can involve the use of indigenous natural enemies to augment
existing populations or to alter the environment to improve conditions for
enhanced natural enemy activity.
Biosynthesis
The synthetic reactions of cell metabolism.
Biotechnology
Any technique that uses living organisms, or substances from those organisms to
make or modify a product, to improve plants or animals, or to develop
micro-organisms for specific uses. Traditional biotechnology covers well established
and widely used technologies based on the commercial use of living organisms.
Modern biotechnology encompasses technologies based on the use of: recombinant
DNA technology; monoclonal antibodies and new cell and tissue culture
techniques.
Bottle-necks
Like the narrow neck of a bottle through which all contents must pass, a
'bottle-neck. In genetic terms, a population with reduced genetic variation due
to exposure to limited conditions.
Branched-Chain Amino Acids
Amino acids whose side chain chemical structrue is branched. Examples include leucine, isoleucine and valine.
Broadcast application
Application over an entire area rather than only on rows, beds or middles (also
referred to as blanket application).
Broad-leaved plants
In general, those that are not mosses or grass-like plants.
Broad-spectrum
A non-selective herbicide affects a wide range of weeds.
Callus
Tissue overgrowth around a wound or canker. A hard protuberance; the new tissue
produced at the base of a cutting or when a part is severed or injured.
Superficial unspecialised tissue produced by plants
in response to wounding. Parenchymatous tissue of
cambial origin that forms in response to wounding. A mass of thin-walled cells,
usually developed as the result of wounding or infection.
Cambium
A layer of actively dividing cells in plants producing new tissues eg. fasicular producing new
vascular tissue, cork cambium producing cork tissue.
Carbohydrates
Starches, sugar, cellulose, fibres and woody
materials. They are composed of carbon, hydrogen, and oxygen in the ratio of 2
molecules of hydrogen to 1 of oxygen. They are a major source of energy for the
animal.
Carotene
A yellow pigment in green leaves and other plant parts. It is the predecessor
of Vitamin A.
Carotenoid
A plant pigment that protects chlorophyll from being photodegraded; enzymes that aid in the production of carotenoids are the target site of herbicides belonging to
the pigment synthesis inhibitor mode of action.
Caryopsis
The seed (grain) or fruit of grasses, including that of cereals.
Catalyst
The speeding up of a chemical reaction by lowering the activation energy, often
through addition of a substance that accelerates the reaction but is not used
up in the reaction.
cDNA
Complementary DNA produced via a mRNA template using the enzyme reverse
transcriptase.
Cell
The living cell includes protoplasm, nucleus and cytoplasm within its walls. An
individual biological unit, capable of independent function and able to divide
to form two new identical cells.
Cell
culture
The growing of cells in vitro. A group or colony of cells propagated from a
single cell in a specifically formulated nutrient medium.
Cell
membrane
A thin envelope surrounding the cell through which food materials pass in and
waste materials and other metabolic products pass out.
Cell Membrane Disrupters
Mode of action of a group of herbicides that kill by destroying cell
integrity.
Cell
nucleus
A spheroid body within a cell distinguished from the rest of the cell by its
denser structure. It is responsible for the functional activity and continued
life of the cell.
Cellulase
An enzyme that breaks down cellulose.
Cellulose
A carbohydrate composed or repeating units of the sugar glucose linked in a
specific way (ß-1,4 linkage); often a main component of plant and algal cell
walls.
Cell Wall
A thin, mechanically strong structure surrounding all plant cells
consisting of a complex mixture of polysaccharides and other polymers that are
secreted by the cell and are assembled into an organized network linked
together by a mixture of covalent and noncovalent bonds. Cell walls regulate cell volume and determine cell shape.
Cereal
A grass grown for its edible seed or grain, such as maize, wheat and rice.
Cerebellum
The posterior section of the brain concerned with the co-ordination of
movement.
Certainty-equivalent
The risk-free return on capital which gives the same level of satisfaction as
other combinations of risk and return.
Certified
Crop in which plants are true to type, and incidence of designated pests and
diseases does not exceed specified tolerance levels.
Certified
applicator
Commercial or private applicator qualified to apply restricted-use pesticides
as defined by the appropriate government authority.
Certified
seed
Seed produced from foundation, registered or certified seed authoritatively
endorsed as being as represented, for use in commercial crop production.
Chemical
name
Scientific name of the active ingredient(s) found in the formulated pesticide.
Chi-square
statistic
A statistic having the distribution of a sum of independent squared standard
normal variables. The number of independent squared normal variables is called
the degrees of freedom.
Chisel
plough
An implement, with points about 30 cm apart, used to till the soil some 30-45
cm deep.
Chloroacetamides
Family of herbicides that inhibit shoot inhibition and belong to the
seedling growth inhibitor mode of action.
Chloroplast
The organelle in plant cells that contains chlorophyll and is the site
of photosynthesis.
Chromatid
The half chromosome appearing during certain phases of cell division.
Chromatography
A method of separation and identification of closely related chemical
substances by their differential movement on or through certain materials, such
as paper and resins, and by their specific colour reactions with certain reagents.
Chromosomal
aberration
An abnormality of chromosome number or structure.
Chromosome
A thread-like body found in cell nuclei, comprised of genes arranged in linear
order. In higher organisms chromosomes consist of DNA in association with
protein. While genes are the units of heredity, chromosomes are the units of
transmission from one generation to the next. During cell division chromosomes
may break, rejoin or cross over giving rise to new genetic combinations. A
unit of hereditary material composed of 1000's of genes. During cell division
chromosomes duplicate and divide, maintaining the genetic integrity of the
organism.
Clone
A collection of genetically identical cells or organisms derived asexually from
a common ancestor eg. a group of plants originating
by vegetative propagation from a single plant
Cloning
In this process one gene is isolated and inserted into a vector which has the
capacity to transport genes into a host cell. Ideally the vector replicates
itself and the gene which it is to carry inside the host.
Coding
The process by which the sequence of nucleotides within a certain area of RNA
determines the sequence of amino acids in the synthesis of the particular
protein.
Coding
sequence
The region of a gene is expressed i.e. translated into protein.
Codon
A coding unit. A sequence of three purine and pyrimidine bases on DNA or messenger RNA that codes for a
specific amino acid.
Coefficient
of correlation
A number that measures the linear dependence between two random variables.
Limiting values of -1 and +1 indicate perfect negative and perfect positive
correlation, respectively; a correlation of zero suggests a complete lack of
association between the two variables.
Coefficient
of selection
A measure of the relative change in gene frequency between generations as a
result of differential selection.
Coenzyme
A low-molecular-weight chemical activating or accelerating enzyme action.
Cofactor
Compound or element that is required for the efficient performance of enzyme
activity.
Cohort
A group of individuals all born at the same time and thus all of the same age.
Used to denote a model where separate ages of each cohort are kept track of as
opposed to a dynamic pool model.
Coleoptile
The sheath covering the first leaf of a grass seedling as it emerges from the
soil.
Common
herbicide name
A common chemical name given to a herbicide by a recognised committee on herbicide nomenclature. Many herbicide are known by a number of
trade or brand names but have only one recognised common name e.g. the common name for Roundup herbicide is glyphosate.
Competition
Occurs when two or more populations, interfere with or inhibit one another
through striving against each other to secure some resource that is in limited
supply e.g. the active demand by weeds for nutrients, moisture, light and other
essential growth factors adversely affecting crop yields.
Competitive Inhibitor
A molecule which has a similar structure as the normal substrate an
enzyme acts upon. A competitive inhibitor inhibits an enzyme's activity by
directly competing with the normal substrate in binding to the active site on
the enzyme.
Compound
A specific association of atoms held together by strong chemical bonds, e.g.
oxygen gas (O2) and water (H2O).
Conjugate
A water soluble derivative of a chemical formed by its combination with glucuronic acid, gluthathione, sulphate, acetate, glycine etc.
Conjugation
Attachment of a molecule (herbicide) to another molecule like sugar,
lipid, lingnin, cellulose, which inactivates the
original molecule.
Contact
herbicide
A herbicide that does not move from the point of initial uptake.Herbicide that kills those plant parts with which it comes into
contact (as opposed to translocated herbicide). Often
acting on the membrane systems of leaf tissues and inhibiting photosynthetic
and respiratory metabolism.
Contact
pre-emergence herbicide
Application of a contact herbicide to weeds before the treatment crop has
emerged.
Controlled
drop application
A term used loosely to describe spinning disc and other systems intended to
produce spray droplets of uniform size.
Cool-season
grass
Grass that grows most luxuriantly during the cool seasons of the year.
Correlation
coefficient
A measure of the degree of the linear relationship between two variables.
Cotyledon
The first leaf or leaves produced by the embryo of a flowering plant.Seed leaf:
leaf-like structures in the embryos of seeds. Grasses have one cotyledon in
each seed (monocotyledon), while legumes have two (dicotyledon).
Cotyledon-leaves
The first leaf, or pair of leaves - depending on whether the plant is
monocotyledonous or dicotyledenous - developed by the
embryo of seed plants.
Cover
crop
A crop grown to maintain a plant cover on the land to prevent erosion and
leaching. When turned under to improve the soil, it becomes a green-manure
crop.
Crop
Community of plants grown to provide feed, food, fibre or other useful commodities.
Crop
diversification
Cropping system where a number of different crops are planted in the same
general area and may be rotated from field to field, year after year.
Cropland
Land used regularly for the production of crops, except forest crops.
Crop
loss
A reduction in either quantity and/or quality of yield. The detriment caused by
the pests expressed in the market as monetary values.
Crop
loss (economic)
Direct loss per unit area (i.e. expected yield minus actual yield). The
assessment of economic losses is the ultimate objective of work on crop loss.
Cross-pollination
Placing or deposition of the pollen from a flower to the stigma of a flower of
another plant.
Cross-resistance
Often weeds will have resistance to more than one herbicide. Those
herbicides may or may not be in related chemical families. Plants with
cross-resistance possess one mechanism that provides the ability to withstand
herbicides from different chemical families. For example, a single point
mutation in the enzyme acetolactate synthase (ALS) may provide resistance to the sulfonylurea
and imidazolinone herbicide families. There are many
different mutations and amino acid substitutions that can endow a plant with
resistance to more than one family of ALS inhibitor herbicides.
Culm
A monocotyledonous stem which is usually hollow except at the nodes or joints.
Cultivar
An agricultural, horticultural or forestry variety, which, when reproduced
(sexually or asexually) retains its distinguishing features, as distinct from a
botanical variety. A cultivar name should always be written with a capital
letter and given single quotation marks, e.g. banana 'Gros Michel'.
Cultural
control
A pest control method in which normal agronomic practices, tilling planting,
crop spacing, irrigating, harvesting, waste disposal, crop rotation are altered
so that the environment is less favourable for the
pest (Stirling, 1985) The application of agronomic,
agricultural and silvicultural practices etc. to
control pests e.g. ploughing under of crop residues,
pruning and destruction of infected tree branches, crop rotation (van den
Bosch, 1980).
Cuticle
Waxy layer of material on the surface of the plant epidermis to help
plants retain water and resist microbe invasion
Cyclohexanediones
Family of herbicides that belong to the lipid synthesis inhibitor mode
of action (dims).
Cytochrome P450
Also known as cytochrome P-450 monooxygenases or CytP450s; multifunctional enzymes widely
distributed among living organisms. They function as monooxygenases by binding and activating molecular oxygen, incorporating one of its atoms into
an organic substrate, and reducing the second atom to form water.
Cytochromes
Proteins essential for oxidation-reduction processes in cells.
Cytokinins
Plant growth-regulating chemicals which promote cell division in cells of
various plants; endogenous cytokninis are mostly
N6-substituted adenine derivatives.
Cytology
The science of the structure, function and life history of the cell.
Cytoplasm
The material enclosed by a cell wall in which are situated the nucleus,
endoplasmic reticulum, mitochondria and other organelles.
Cytosol
The liquid substance of protoplasm, excluding all the organelles such
as nuclei, plastids, ribosomes.
Deciduous
Plants or trees that shed leaves or awns at a
particular season or stage (leaf loss may also be induced by drought etc.).
Degradation
A general term applied to the breakdown of toxic components by biochemical
processes into non-toxic products.
Dehydrogenase
A class of enzymes which oxidise substrates in the
process of removing electrons and hydrogen atoms.
Denatured protein
Protein whose properties have been altered by treatment with physical or chemical
agents.
Deoxyribonucleic acid
DNA A polymer of nucleotides connected via a phosphatedeoxyribose sugar backbone; the genetic material of the cell. A polymer composed of the
sugar deoxyribose and of nucleic acid bases arranged
in such a fashion as to encode the inheritable traits of an organism; the
genetic material of an organism.
Diallel cross
The genetic intercrossing of parents in all combinations of two; all possible
crosses among individuals in a group.
Dicotyledon
Having two cotyledons in each seed, e.g. beans, including flowering plants
which are not monocotyledons, the majority of annual weeds and many perennial
weeds.
Dinitro
A common designation for dinitro-phenols. These
materials are used as contact chemicals, as crop defoliants or as a control for
succulent annuals.
Dinitroanilines
Family of herbicides that inhibit microtubule assembly and belong to
the seedling growth inhibitor mode of action (DNA).
Diphenylether
Family of herbicides belonging to the cell membrane disrupter mode of
action.
Diploid
Having two homologous chromosomes in pairs in the nucleus so that twice the
haploid number is present, usually written as 2n.
Direct drilling
Drilling seed directly into soil without any mechanical seedbed preparation
e.g. tilling since the previous crop.
Directed application
Placement of spray or dust, of for example a herbicide, so as to avoid or minimise contact with the crop e.g. as a row or bed or to
the leaves or stems of weeds.
Dispersal
Movement and spread of weeds.
Dispersal unit
Seed plus associated tissues of flower, fruit or specialised leaves. Any device for spread and survival that can be recognised visually and counted.
DNA
Deoxyribonucleic acid, the macro-molecular polymer which carries the genetic
hereditary message and controls all cellular functions in most forms of life.
The twin strands, in the form of a helix, are composed of successive units of
the sugar de-oxyribose, phosphate and the bases
adenine, cytosine, guanine and thymine, through which the twin strands are
cross-linked: adenine to thymine and cytosine to guanine.
DNA Markers
DNA sequences that are found at specific loci in species that may vary
in sequence among members of that species.
DNA Polymerase
The enzyme which catalyzes the reaction of adding new DNA bases to a
growing DNA strand.
DNA Replication
The process in which a DNA molecule is copied. This takes place in PCR
and naturally in cell division.
DNA Sequence
The order of nucleotides, whether in a fragment of DNA, a gene, a
chromosome, or an entire genome.
Dominant
The allele that is expressed in a heterozygous organism. A heritable
character possessed by one parent of a hybrid which, when pure, will express
itself in the hybrid to the apparent exclusion of the opposite or recessive
character in the other parent.
Dominant gene
A gene that is fully expressed in the phenotype of the heterozygote.
Dormancy
Condition of relative inactivity as applied to seeds, tubers and perennial
plants during the winter.
Dormant
Temporary suspension of visible growth and physiological activity evidenced in
many plants by loss of leaves.
Dosage rate
The amount of active ingredient dispensed per unit area. It could be mixed with
a wide range of quantities of carrier medium. The dosage is constant, but the
application rate may vary.
Dose: Dosage
Quantity of herbicide applied per unit area.
Dose-response curves
Demonstrate the relation between dose and the proportion of individuals
responding with a quantal effect. In general,
dose-response curves are S-shaped (increasing), and they have upper and lower
asymptotes usually but not always 100 and 0%.
Double Helix
The spiral shape that two linear strands of DNA assume when bonded
together.
Drift
Movement of droplets/dust in natural air currents beyond the intended area of
application.
Drill
To sow in furrows.
Droplet spectrum
Distribution (by number or volume of droplets) of spray into intervals of
droplet size.
Ear
The heavy spike of spike-like inflorescence, such as the ear of wheat.
Economic damage
The amount of injury which will justify the cost of artificial control
measures.
Electron-transport phosphorylation
Synthesis of ATP involving a membrane-associated electron transport chain and
the creation of a proton-motive force. Previously termed oxidative phosphorylation.
Electrophoresis
A technique used to separate chemical substances according to the electrical
charge on their molecules which migrate in response to the application of an
electric field.
ELISA (Enzyme-Linked ImmunoSorbent Assay)
A test which can be used to detect the presence of proteins encoded by
a specific gene.
Embryo
The undeveloped plant in a seed.
Emergence
Germination of a seed and the appearance of the shoot. The time when the first
leaves of the crop plant come through the ground.
Endoplasmic reticulum
A complex pattern of internal membranes that permeates the cytoplasmic matrix of eucaryotic cells.
Endosperm
The starchy or oily nutritive material that surrounds the embryo in some seeds
(sometimes referred to as albumen); it is triploid, having arisen from the
triple fusion of a sperm nucleus and the two polar nuclei of the embryo sac.
Enzyme
A protein that catalyzes, or speeds up, a specific biochemical reaction
without changing the nature of the reaction and without being changed in the the chemical reaction.
Enzyme-linked immunosorbant assay (ELISA)
A serological test in which the sensitivity of the antibody-antigen reaction is
increased by attaching an enzyme to one of the two reactants.
Ephemeral
Plant with a short life-cycle, producing several generations in a year; flowers
persisting for one day only.
Epinasty
Downward curling of a leaf blade due to cell growth on the upper side of a
petiole being more rapid than that on the lower side; often caused by phenoxy herbicides
EPSPS
5-enolpyruval-shikimate-3 phosphate syntheses; an enzyme essential for
amino acid production that is the target site for glyphosate (Roundup).
Essential Fatty Acids
Fatty acids that are not synthesized by the human body, but are
necessary for normal growth and life. These essential fatty acids are the linolenic and linoleic acids, and
must be obtained from the diet.
Ester
A form in which some types of weed-killers may be prepared, notably 2,4-D and
2,4-5T. Weed-killers prepared as esters are not soluble in water. They are
dissolved in oil to which an emulsifier is added so that it may be diluted with
water.
Ethylene
A plant hormone produced by most plant tissues involved in fruit
ripening, seed germination, senescence, abscission, and other aspects of plant
development.
Etiolation
Excessive spindliness in plants, owing to
insufficient light or to disease. A phenomenon exhibited by plants grown in the
dark; etiolated plants are pale yellow and have long internodes and small
leaves.
F1
The first filial generation, or the first-generation offspring of a given
mating.
F2
The second filial generation. It is in this generation that segregation first
occurs.
Fallow
The practice of leaving land either uncropped and weed-free, or with volunteer vegetation during at least one period when a
crop would normally be grown; objective may be to control weeds, accumulate
water, and/or available plant nutrients.
Fatty Acids
A class of compounds containing a long hydrocarbon chain and a terminal
carboxyl group. Fatty acids can be saturated (containing no carbon-carbon
double bond), monounsaturated (containing one carbon-carbon double bond), or
polyunsaturated (containing multiple carbon-carbon double bonds).
Fecundity
Reproductive capacity of a weed.
Floret
Lemma and palea with the enclosed flower, they may be
bisexual and perfect, or unisexual and male or female or infertile. Individual
small flower, as in grasses or composites.
Foliage applied herbicides
Compounds penetrate the outer waxy cuticle and are absorbed into the leaf
tissue, where they may or may not be translocated basipetally in the phloem.
Free Radical
Any molecule with one unshared electron giving the molecule a partial
negative charge; highly reactive and can cause permanent damage to cellular
membranes.
Frequency distribution
A specification of the way in which the frequencies of members of a population
are distributed according to the values they exhibit.
Gamete
A mature male or female reproductive cell (sperm or ovum) containing
half of the total number of chromosomes in a cell (i.e., humans have 46
chromosomes per cell; gametes would have 23).
GC/MS
Gas-liquid chromatograph coupled to a mass
spectrometer
Gel-chromatography
A molecular sieving procedure, by which viruses are separated from different
sized molecules when passed through the pores of gel beads such as agarose. Used for virus purification.
Gene
The fundamental unit of heredity that carries genetic information from
one generation to the next. A gene is an ordered sequence of nucleotides
located on a particular position on a particular chromosome that encodes a
specific functional protein.
Gene Action
The phenotypic response observed when the dosage of an allele changes.
For example, in the allelic series AA, AB, and BB, the dosage of the B allele
changes from 0 to 1 to 2. Gene action may be additive (if AA<AB<BB),
dominant (if AB=BB), or overdominant (if AB>BB).
Gene Cloning
Finding and making copies of a specific gene. This is the first part of
the genetic engineering process.
Gene Expression
The production of a protein encoded by a gene. Gene expression is
controlled by the promoter region of the gene.
Gene expression
Evidence or manifestation of a genetically controlled characteristic. All of
the chromosomal genes in an organism are not active at all times. In a plant
nucleus as little as 5% of the DNA may be producing protein at any one time.
Gene Flow
Movement of genes among and between species or populations.
Gene Library
A collection of cloned DNA molecules representing all or part of an
individual's genome.
Gene Mapping
Determination of the relative positions of genes on a DNA molecule or
chromosome and the distance between them.
Gene Silencing
The inactivation of a gene by an organism to prevent the gene from
expressing.
Gene Stacking
Creating a plant with a desired combination of two or more unique
genes. This can be done when the genes are first transferred into the cells by
co-transformation, or during the breeding process by crossing two lines that
each contain a different gene resulting in progeny with both genes.
Genetic Code
The sequence of nucleotides, read three at a time, that determines the
order of amino acids in a protein. The nucleic acids, DNA (deoxyribonucleic
acid) and RNA (ribonucleic acid) are the molecular substances in the cell
nucleus, that are carriers of genetic information and are thus the basic
genetic material in all living things. DNA occurs in the form of a double helix
which acts as a template to reproduce itself. RNA is concerned with carrying
the genetic information to the cytoplasm of the cell and establishing the
genetic specifications there. Each of the various DNA assemblies can be called
a gene.
Genetic Engineering
The process of adding foreign DNA to the genome of an organism.
Genetic Fingerprinting
Determining the genetic makeup of an organism with the use of DNA
markers.
Genome
The entire hereditary message of an organism. The total genetic composition of
the chromosomes in the nucleus of a gamete. The nucleic acid component of a
virus.
Genomic library
A collection of recombinant DNA molecules or clones which collectively comprise
the total genome of an organism.
Genotype
The entire genetic make up of an organism, expressed
and latent, dominant and recessive. The individuals of the same genotype breed
alike. A group of organisms with the same genetic make up.
Contrast with phenotype.
Genus
The principal subdivision of a family next above a species. A group of related
species with similar characteristics and appearing to have a common ancestry.
Germination
The process in which a dispersal unit, e.g. a fungal spore or seed, under
specific environmental conditions, assumes increased metabolic activity,
resulting in the production of new structures, most often a germ tube or growth
of embryo in a seed.
Gibberellins
A group of plant growth-regulating substances with a variety of functions.
Glyphosate
A broad spectrum herbicide which inhibits the production of amino
acids.
Grass
Botanically, a plant of family Gramineae.
Graminicide
Herbicides that target the grass family (Graminae);
refers to the lipid synthesis inhibitor herbicides that or only effective on
grasses.
Growth Regulators
Mode of action of herbicides that mimic plant hormones causing
unregulated growth.
Growth stage
A morphologic phase of plant or crop development that can be easily recognised in the field.
Guard Cells
Specialized epidermal cells that form the boundaries of stomata, the
pores in plant leaf surfaces.
Haploid
Having one set of chromosomes in a cell or an individual. Haploidy is a characteristic of sex and germ cells.
Herbicide
Any substance or mixture of substances intended for preventing, destroying or
controlling any weed, including any algae or aquatic weed.
Herbicide Family
A group of herbicides that have similar chemical structure and kill
plants by the same mechanism of action.
Herbicide, residual
Herbicide showing persistent effect when applied to soil.
Herbicide Resistance
The inherited ability of a plant to survive and reproduce following
exposure to a dose of herbicide normally lethal to the wild type. In a plant,
resistance may be naturally occurring or induced by such techniques as genetic
engineering or selection of variants produced by tissue culture or mutagenesis.
Herbicide, selective
Herbicide possessing differential toxicity to certain weeds and crop plants.
Herbicide Tolerance – Term is no
longer used as it is confused with resistance.
The inherent ability of a species to survive and reproduce after
herbicide treatment. This implies that there was no selection or genetic
manipulation to make the plant tolerant; it is naturally tolerant.
Heritability
The proportion of phenotypic variation that is due to genetics, as
opposed to environment or genotype x environment interaction.
Heterosis
Increased growth, vigour or yield frequently shown in
the F1 generation of a cross. Hybrid vigour.
Heterozygous
An organism that has two different alleles at one or more locations on
a chromosome.
Homozygous
Of a cell or organism having both genes of a pair dominant or recessive an
organism may be homozygous for one, several or all genes.
Homozygote
An individual the parent of which contributed to it a similar number of any
given number pair of genes and whose germ cells are all alike in regard to the
genes for that character.
Hormone
A chemical agent that controls various physiological processes within a plant.g. auxins and cytokinins in plants stimulate cell proliferation and
growth.
HPLC/MS
High performance liquid chromatograph coupled
to a mass spectrometer.
Hydrophilic
Having chemical properties relating to water (water-like). Compounds are polar or ionizable and can be soluble in water; lipophobic.
Hydrophobic
Water "fearing"; compounds that are relatively insoluble in
water and other polar solvents and soluble in lipids and other nonpolar solvents.
Hybrid
The first generation offspring of a sexual cross fertilisation between two individuals differing in one or more genes i.e. a heterozygote.
Imidazolinones
A family of herbicides that are similar in chemical structure (imidazolinone ring) and have the same mechanism of action -
amino acid synthesis inhibition.
Inbred
A normally cross-pollinated plant that has been self-fertilised.
Inbreeding depression
Loss of vigour and increased mortality in successive
generations due to inbreeding.
Indeterminate
A plant that flowers over a long period; ripe seeds, blossoms and vegetative
shoots may be present on the plant at the same time. The terminal flowers tend
to be the last to open, so that the floral axis may be prolonged indefinitely
by a terminal bud.
Induced enzyme
An enzyme subject to induction.
Inducible enzyme
An enzyme whose synthesis does not occur unless a specific chemical, called an
inducer, is present; the inducer is often the substrate of that enzyme.
Ingredient, active
The chemical(s) in a herbicide formulation responsible for its toxicity to
weeds.
Inhibit
To hold in check or stop, as to inhibit or check seed germination or plant
growth with chemicals.
Inorganic compound
A compound which does not contain carbon atoms (the only exception being carbon
dioxide CO2).
In situ
In the original situation.
Integrated weed management
The use of more than one method (biological, chemical, cultural etc.) to control
weeds.
Intercropping
The growing of two crops simultaneously in the same field.
Internode
The portion of the stem between two nodes or joints.
Introgression
The entry or introduction of a gene from one gene complex into another.
Intron
A eucaryotic DNA segment that does not code for
protein but may interrupt segments which do encode protein. Contrast with Exons, the coding sequences.
Inactivate
The process of making a herbicide non-herbicidal by degradation or
bonding to another molecule.
Incomplete Dominance
Expression of a heterozygous phenotype which is different from, and
often intermediate to, that of either homozygous parent.
Inflorescence
The arrangement of flowers on a stem; inflorescence types include corymb, cyme, head, panicle,
solitary, raceme, spike thyrse, and umbel.
Interphase
The stage of cell division when DNA is replicated; a copy of each
chromosome is made.
Intron
A portion of DNA located between coding regions in a gene which is
transcribed, but spliced out of the mRNA before translation. This region of
nucleotides does not actually code for any proteins.
Isoenzyme
One or more forms of an enzyme having catalytic properties ascribed to that
enzyme.
Isomer
Briefly, two compounds are said to be isomeric if they are composed of the same
elements in the same proportion by weight but have different chemical and
physical properties.
Jointing stage
The stage when grass stems begin elongating.
Kernel
Whole grain of a cereal; the mature ovule.
Krebs cycle
A cyclical series of steps in which pyruvate is oxidised through the mediation of several organic acids.
L-arginine
A common amino acid of proteins: H2N-C(=NH)-NH-CH2-CH2-CH2-CH(NH2)CO2H.
Label
The written, printed or graphic matter on, or attached to, the herbicide, or
the immediate container thereof and the outside container or wrapper of the
retail package (if there are any) of the herbicide.
Lamina
Leaf blade.
LD50
The dose of chemical that can kill 50% of the test subjects.
Life cycle
The complete succession of changes undergone by an plant during its life.
Ligase
An enzyme that can rejoin cut strand of DNA.
Lignin
The complex phenolic polymer that endows the
xylem and other tissues in plants with compression and decay resistance.
Linkage
The association of genes on the same chromosome. The shorter the
distance between two genes, the greater the probability they will be inherited
together.
Lipid
Group of organic compounds which are esters of fatty acids and which are characterised by being insoluble in water but soluble in
many organic solvents.
Lipid Bilayer
Made up of compounds which have both hydrophobic and hydrophilic
moieties, this is the structure of membranes such as the cellular membrane.
Lipid Synthesis Inhibitors
Mode of action of herbicides that target the production of lipids which
are essential in plant growth and function.
Lipophilic
Having chemical properties relating to lipids (lipid-like), nonpolar compounds that are highly soluble in organic
solvents, but not water; hydrophobic.
Locus
The site on a chromosome where a particular gene (or other sequence) is
located (plural=loci).
Lysine
Nonessential amino acid found in cheese, eggs, milk, meat, legumes,
whole grains, and nuts.
Lysis
The dissolution or destruction of cells by the disruption of the cell
membrane.
Marker
An easy to detect trait controlled by a known gene. Markers, such as
antibiotic or herbicide resistance, are often used to determine if an organism
is transgenic.
Marker Gene
A gene controlling an easily detectable trait used to select transgenic
cells or plants from non-transgenic ones, (i.e., herbicide and antibiotic
resistance).
Mechanism of Action
The specific process inhibited by a herbicide.
Meiosis
The process of division of sexual cells in which the number of chromosomes in
each nucleus is reduced to half the normal number found in normal somatic
cells. When two sexual cells fuse, each contributes its half of the
chromosomes. The resulting embryo contains the full chromosome complement.
Cells with half the chromosomes are called haploids, while those with the full
complement are diploids.
Meristems
Area of cell division.
Mesophyll
Layer of chloroplast-containing cells between the epidermal layers of a leaf.
Soft wood. The leaf parenchyma cells between epidermal layers.
Messenger RNA (m-RNA)
m-RNA carries the genetic code for a protein from the DNA to the ribosomes where the code is read and the protein
manufactured. A chain of ribonucleotides that codes
for a specific protein.
Metabolism
A general term referring to the change of a herbicide from an active to
an inactive state.
Metabolite
A product of metabolism - formed by biochemical interaction upon a substance
introduced into the normal system of an plant.
Methionine
An essential amino acid found in cereal, whole grains, sesame and
sunflower seeds, and yeast.
Micro-tubules
Tubes that are the structural entity for eucaryotic flagella, have a role in maintaining cell shape, and function as mitotic
spindle fibres.
Minor resistance genes
Confer a low level of resistance but it is thought that they may, when
aggregated in a single genotype, give a high level of resistance that is
durable.
Mitochondria
Minute bodies in the cytoplasm of a cell which are responsible for respiration
and specialised reactions. The enzymes they carry catalyse the biochemical processes of cell respiration and
the anabolic conversion of simple substances into compounds which store
chemical energy.
Mitosis
The normal process of the division of somatic cells (i.e. non-sexual cell) in
which the chromosomes are duplicated longitudinally to give two daughter nuclei
each having a chromosome complement equal to that of the original nucleus
(parent).
Mixed function oxidases
Oxidising enzymes which are involved in the
metabolism of many foreign compounds giving products of different toxicity from
the parent compound.
Mode of action
A term used to describe the way or method by which a herbicide may alter or
adversely affect physiological or biochemical events in an weed resulting in a
toxic effect, usually ending in death.
Molecular Marker
An identifiable DNA sequence on a chromosome. A marker can be a gene,
part of a gene, or a sequence in a non-gene region. SSR, RFLP, RAPD, and AFLP
are acronyms for commonly used marker techniques.
Monocotyledon
Any seed plant (angiosperm) having a single cotyledon or seed leaf. Leaves are
mostly parallel veined e.g. cereals, grasses, rushes and sedges and various
weeds
Monoecious
Refers to plants that have separate male and female flowers on the same plant,
Monoculture
The growing of a single crop species continuously or in successive seasons over
a wide area.
mRNA
Messenger RNA, a molecule which is synthesized from a DNA template by the
enzyme RNA polymerase.
Multi-genic
Normally relating to resistance controlled by more than one gene.
Multiple alleles
A series of alleles or alternative forms of a gene.
Multiple genes
Two or more independent pairs of genes which produce complementary or
cumulative effects upon a single character of the phenotype.
Multiple-resistance
Plants with multiple-resistance possess more than one mechanism that
provides plants the ability to withstand herbicides from different chemical
families. In this case, herbicide options become very limited. A Kochia scoparia population was
identified that was target-site resistance to the PS II inhibitor herbicide, triazine, and to ALS inhibitor herbicides. The plants
carried two mutations, one for resistance to each class of herbicide. Weed
populations also may have multiple herbicide-resistance mechanisms. For
example, a Lolium rigidum population in Australia has target-site resistance to ACCase and to ALS inhibiting herbicides. In addition, it has metabolism-based
resistance to a number of other herbicides from different chemical classes.
There is evidence that different cytochrome P450s are
responsible for the increased metabolism.
Mutant
An individual having an abnormal structure, property or behaviour in which it differs distinctly from the parent plant from which it was derived.
This is an inheritable change (a change in the sequence or chemistry of the purine or pyrimidine bases
contained in DNA molecules) and may be caused or induced by high energy
irradiation or by certain chemical substances.
Mutation
A suddenly occurring heritable change in DNA. Such mutations may be brought
about by chemical or physical agents (mutagens) e.g. U.V. radiation. An abrupt
appearance of a new characteristic in an individual as a result of an
accidental change in genes or chromosomes. 1. The process by which a gene
undergoes structural change. Any change in a DNA sequence.
NADPH
Reduced nicotinic adenine dinucleotide phosphate
Natural selection
The selection among a group of organisms by the forces of nature which allows
those of the group best fitted to survive in the particular environment to live
and reproduce, while those not fitted to survive die. By this means, the
species or group survive and adapt to the environment, the less well adapted
members being gradually eliminated over many generations.
Necrosis
A localised and rapid destruction of a cell or more
often a group of cells and a consequent quick death of those which are in
contact with or form part of a living tissue; rot and canker are examples of
necrotic symptoms.
Necrotic
Having symptoms characterised by the death or
disintegration of cells or tissues.
Negative Cross Resistance
Occurs when a resistant biotype is more susceptible to other classes of
herbicides than the susceptible biotype.
Non-ionic surfactant
A surfactant that does not ionise in solution and is
therefore compatible with both anionic and cationic surfactants.
Non-selective herbicide
A chemical that is generally toxic to plants without regard to species;
toxicity may be a function of dosage, method of application etc.
No-Till
Lack of any tillage at all. The soil is not broken except for planting
and maybe for some fertilization.
Normal distribution
A continuous probability distribution commonly used in statistics and
completely characterised by a mean µ, which is
symmetric about, and a variance _², which describes the spread of the
distribution. The distribution is denoted by N(µ_²).
Noxious weed
a weed arbitrarily defined by laws as being especially undesirable, troublesome
and difficult to control. definition will vary according to legal
interpretations.
Nucleic acid
a dna or rna molecule which
may be composed of one or two strands. a compound of high molecular weight that
consists of pentose (ribose (rna) or deoxyribose (dna)), phosphoric
acid, and nitrogen bases (purines and pyrimidines), present in all living things including the
infectious parts of plant viruses.
Nucleotide
A subunit of DNA or RNA consisting of a nitrogenous base (adenine,
guanine, thymine, or cytosine in DNA; adenine, guanine, uracil,
or cytosine in RNA), a phosphate molecule, and a sugar molecule. Thousands of
nucleotides are linked together to form a DNA strand.
nucleotide sequence
the order of nucleic acid bases in a dna or rna strand.
nucleus
membrane-enclosed protoplasmic body structure within eucaryotic cells containing the genetic material (dna) organised in chromosomes.
Oil Additives
An additive made either synthetically or extracted from seeds that
enhances herbicide uptake into the plant; crop oils, methylated seed oils, crop oil concentrates.
Open pollination
Pollination without control so that the male parent is not known.
Operon
A group of genes which function as a collective unit. A cluster of genes whose
expression is controlled by a single operator.
Organelles
Organised micro-structures within cell cytoplasm,
having specialised biochemical functions, e.g.
chloroplasts, mitochandria. A structure found within
an individual cell which has a specific function e.g. mitochondion for cellular respiration.
Organic compound
A compound other than carbon dioxide (CO2) which contains one or more carbon
atoms; when there is more than one carbon atom, carbon atoms are usually bonded
to each other.
Outcross
Cross-pollination, usually by natural means, with plants differing in genetic
constitution.
Ovule
An immature seed which develops into a seed after fertilisation.
Oxidation
Removal or exchange of electrons usually by combining with oxygen.
P-680
The reaction center of photosystem II which
best absorbs light at a 680 nm wavelength. P-680 is a chlorophyll a molecule.
P-700
The reaction center of photosystem I which
best absorbs light at a 700 nm wavelength. P-700 is a chlorophyll a molecule.
PAT
The enzyme that controls resistance of glufosinate herbicide by detoxifying the herbicide molecule.
Pathway
A sequence of interconnecting enzyme reactions.
Parenchyma
The plant tissue consisting of cells concerned with physiological activities
i.e. capable of photosynthesis or storage, as distinguished from supportive
tissue.
Parthenocarpic
The production of fruit without pollination.
PCR
(polymerase chain reaction) A method for replicating a particular
sequence of DNA in vitro. Used to generate greater amounts of DNA for analysis
or to determine if a particular sequence exists.
PEP carboxylase promoter
Phosphenol pyruvate (PEP) carboxylase is an enzyme used in
photosynthesis. The promoter of this gene induces protein production in
actively photosynthesizing tissues of plants.
Perennial
A plant that lives longer than 2 years from time of seeding, and usually flower
each year. Plants may be herbaceous or woody.
Persistent
herbicide
Herbicide that, when applied at the recommended rate, will harm susceptible
crops planted in normal rotation after harvesting the treated crop, or that
interferes with re-growth of native vegetation in non-crop sites for an
extended period of time.
Phenolic compound
An aromatic hydroxylated compound or a derivative
thereof.
pH
Negative log of the hydrogen ion concentration (pH = -log [H+]), the
higher the pH of an environment the less H+ ion concentration, the more basic
the environment becomes.
Phenotype
The observable physical characteristics of a plant that are determined
by a combination of the genetic composition (genotype) and the environment of
the individual.
Phenotypic Trait
An observable physical characteristic of an plant. See Phenotype.
Phenoxyacetic Acids
A family of herbicides with similar chemical structure belonging to the
growth regulating mode of action. An example would be 2,4-D.
Phloem
Tissue used for the movement of sugars from source tissue to sink tissue;
Composed of living cells called sieve elements that have no nuclei, vacuoles,
or ribosomes. The ends of the sieve elements contain
connective pores, which join them together to form tube-like structures.
Photoinhibition
Reduction in photosynthesis rate at high light intensities that has been
observed for both phytoplankton and terrestrial plants.
Photophosphorylation
The coupling of photosystems I and II with an
electron transfer chain that moves electrons from water (which is oxidized to
form O2) to NADP+ (which is reduced to form NADPH). The transfer of electrons
between photosystem II and photosystem I releases energy, which is conserved in the form of a trans-membrane proton
gradient and used to synthesize ATP.
Photoperiod
Light period of a day. The optimum duration of light and darkness for the
normal growth and maturity of a plant in nature.
Photosensitizers
Molecules which have efficient conversions to the triplet state after
absorption of a photon. These triplet state molecules either reduce other
molecules to generate free radicals, or they excite O2, normally a triplet, to
the excited singlet state; singlet oxygen is very reactive and can cause
significant cellular damage.
Photosynthesis
The enzymatic conversion of light energy into chemical energy and use of this
to form carbohydrates (as a by-product) and oxygen from CO2 and H2O in plant
chloroplasts.
Photosynthetic Inhibitors
The mode of action of a group of herbicides that directly influence the
light reaction of photosynthesis.
Photosystem
An array of pigment-protein complexes and electron transfer components
that function together to harvest light energy, transfer the energy to
photochemical reaction centers, and move the excited electrons in a controlled
fashion to produce usable biochemical energy. Each photosystem contains hundreds of chlorophyll and carotenoid molecules functioning as antennae, while only a few chlorophyll molecules are
employed in the reaction centers.
Phytotoxic
A substance which is toxic to plants.
Pigment Synthesis Inhibitors
The mode of action of a group of herbicides that stops pigment
synthesis (not chlorophyll)i these pigments are
present to protect chlorophyll from breakdown by sunlight. Without the pigments
present, chlorophyll is easily degraded showing bleaching symptoms on plant
tissue.
Plant
growth regulator
A chemical other than a nutrient which can be used to modify plant growth.
Plasmalemma
The cytoplasmic membrane found on the outside of the
protoplast adjacent to the cell wall.
Plasma
membrane
The thin structure enclosing the cytoplasm, composed of phospholipid and protein, in a bio-molecular leaflet structure.
Plasmodesmata
Fine protoplasmic connections between cells which extend through the wall.
Plastid
Specialised cytoplasmic structures in a cell which are the centre of chemical activity.
Pleiotropy
The control of more than one trait by a single gene.
Ploidy
The degree of replication of chromosomes (e.g. haploid, diploid, tetraploid etc.) in an plant.
Pollen
In plants, the male germ cells produced in the anther. When ripe, pollen sacs
at the end of the anthers split open to release the pollen. Each ripe pollen
grain contains two male nuclei equivalent to male gametes.
Polygenic
resistance
Resistance to herbicides based on many genes, i.e. a series of genes
controlling a quantitative character.
Polymerase Chain Reaction (PCR)
The lab procedure which makes copies of DNA much like cells replicate
DNA during cell division.
Polymorphic
Existing in multiple forms. When a marker locus is polymorphic, there
are detectable differences in DNA sequence at that locus.
Polyploid
An organism or cell having more than two complete sets of chromosomes.
Polyploidy
Having more than 2n (diploid) number of basic chromosomes such as
triploid (3n) or tetraploid (4n); very common in
angiosperms.
Postemergence
Application of a herbicide after the plant has emerged.
PPO
Protoporphyrinogen oxidase (protox); enzyme utilized in photosynthesis and is
the target site of many herbicides in the cell membrane disrupter mode of
action.
Pre-emergence
herbicides
A treatment of a fully cultivated field after sowing of the crop seed but
before it has emerged. Selectivity may depend partly on differences on the
rooting depth of crop and weed.
Primer
Small section of DNA nucleotides which bind to the single-stranded DNA
template during PCR. These can be sequences specific for a gene or totally
random, depending upon the experiment’s objective.
Pro-Herbicide
A molecule that doesn't become herbicidally active until a reaction within a plant makes it a herbicide.
Promoter
A specific DNA sequence to which RNA polymerase binds and initiates
transcription. This region contains information which regulates when and how
often the gene is transcribed and ultimately the amount of protein it produces.
Propanoic Herbicides
A family of herbicides that have similar chemical structure and belong
to the lipid synthesis inhibiting mode of action (fops).
Protein
A large molecule composed of one or more chains of amino acids in a
specific order. Proteins are necessary for the structure, function, and
regulation of an organism's cells, tissues, and organs. Each protein has a
unique function determined by its shape.
Protein Synthesis
The production of proteins in a cell. Proteins are chains of amino
acids linked in the order determined by the genetic code.
Protease
An enzyme which degrades protein into their component amino acids.
Protoplasm
All the substance of a cell, usually considered not to include the cell
wall. The protoplasm of a single cell is a protoplast.
Protoplast
A plant cell that has had the cell wall removed.
Protoporphyrin
An intermediate in the biosynthetic pathways for chlorophyll and heme. This molecule is a strong photosensitizer and causes much cellular damage if it accumulates in tissues exposed to light.
Qualitative Characters
A character in which variation is discontinuous.
Quantitative Characters
A character in which variation is continuous so that classification
into discrete categories is not possible.
Quenching
The process of causing the de-excitation of a molecule from an excited
singlet or triplet state back down to the ground state. Quenching of chlorophyll
is an important protective role of carotenoids. If a
triplet molecule is not rapidly quenched, it can react with oxygen to generate
singlet oxygen. Singlet oxygen can cause much cellular damage.
Randomized blocks design
The design used in experimental work in which the treatments are arranged in
random order within the replicates blocks to eliminate bias.
RAPD
Random Amplified Polymorphic DNA. These markers involve PCR
amplification of DNA fragments using primers that are random 10-base oligonucleotides. A single RAPD reaction may amplify
several to many DNA fragments. RAPDs are dominant
markers and, therefore, less informative than codominant markers because heterozygous individuals cannot be identified. A major
advantage is that no prior knowledge of an organism's genome is necessary for
their use. A common problem with RAPDs has been lack of reproducibility among
labs.
Rate and dosage
These terms are synonymous. Rate is the preferred term. Rate refers to the
amount of active ingredient material (such as 2,4-D acid equivalent) applied to
a unit area.
Receptor
Special proteins in the cell membrane that bind to a signal or chemical
messenger from the environment and transmit signals to the cell to initiate a
response.
Recessive
A heritable trait tending to be suppressed by a more active or dominant trait.
Expressed only when present in an plant in the homozygous condition and which
in a heterozygous condition is suppressed by the dominant allele of the pair.
Recessive Allele
An allele whose phenotype is not expressed in a heterozygote.
Reciprocal crosses
Two crosses between two plants in which the male parent of one cross is the
female parent of the second cross.
Recombinant DNA (r-DNA)
A strand of DNA synthesised in the laboratory by
splicing together selected parts of DNA strands from different organisms or by
adding a selected part to an existing DNA strand. DNA that has been altered and
is different from the original sequence.
Recombinant Plasmid
A plasmid that has been cut with special enzymes and
"recombined" in a new order or with DNA from another source.
Recombination Frequencies/Map
Distance
Recombination frequency is the frequency of crossovers between two
genes. The map distance (in this case a genetic or recombinational map) is the recombination frequency between two genes times 100. For example,
if the frequency of recombination is 0.10, the map distance is 10 map units.
Recombination
Process by which genetic elements in two separate genomes are brought together
in one unit. The occurrence of progeny with combinations of genes other than
those that occurred in the parents, owing to independent assortment or crossing
over. Also, a new strain of a virus that occurs as a result of the breakage and
renewal of co-valent links in a nucleic acid chain,
so that the nucleic acids are rearranged in the chain.
Registered
Chemicals that have been approved for use in agriculture by a Ministry of
Agriculture.
Replicates
Repetitions of the same experiment. It is applied in statistics to represent
observations that have the same experimental conditions.
Residual herbicide
Herbicide that persists in the soil and injures or kills germinating weed
seedlings over a relatively short period of time.
Regulatory Protein
A protein that binds to the promoter of a gene to regulate
transcription.
Relative Fitness
The fitness of one genotype when compared with another.
Resistance
The inherited ability of a population to survive and reproduce
following repeated exposure to a dose of herbicide normally lethal to the wild
type. Resistance may also be induced by such techniques as genetic engineering
or selection of variants produced by tissue culture or mutagenesis.
Restriction Enzymes
Enzymes that are able to detect a particular nucleotide sequence and
cut the DNA, RNA, or protein at that location.
RFLP
Restriction Fragment Length Polymorphism. DNA is digested with a
restriction enzyme and the fragments are separated by electrophoresis. The DNA
fragments are then transferred to a membrane and hybridized with a labeled DNA
probe. Polymorphisms are detected as labeled DNA fragments of different sizes.
RFLPs are very informative due to their codominant nature (they distinguish between homozygotes and heterozygotes). Large numbers of RFLP markers are available
for many species. Disadvantages are that they are relatively expensive and time
consuming, and they require a large quantity of DNA. Most commonly, radioactive
labeled probes are used, but non-radioactive methods are also available. The
technique is described in detail in S. Grandillo and
T.M. Fulton (2002), Approaches to gene mapping. pp. 101-136. In P.M. Gilmartin and C. Bowler (ed.) Molecular Plant Biology Vol.
1. Oxford Univ. Press, Oxford and New York.
Rhizomes
A specialized horizontal stem that gives rise to shoots and roots at
its nodes; usually found underground, i.e., iris, rhubarb.
Ribosome
A large molecule that catalyzes the translation of mRNA codons into an amino acid sequence.
RNA
Ribonucleic Acid. A single-stranded
nucleic acid similar to DNA but having a uracil rather than thymine as one of the nucleotides. The RNA strand carries the coded
information from the nucleus to the cytoplasm where protein production occurs.
RNA Polymerase
An enzyme that catalyzes the synthesis of RNA by copying the nucleotide
sequence of the DNA.
Roundup
A herbicide that provides non-selective control of several annual and
perennial weeds. Roundup will also damage crops, such as corn and soybeans that
are not Roundup-resistant.
Roundup-Ready
A trade name given to certain varieties of corn or soybean which are
resistant to the herbicide, Roundup, whose active ingredient is glyphosate.
Roundup-Resistant
A plant that is not harmed by the application of Roundup herbicide,
i.e., Roundup Ready Corn, Roundup Ready Soybeans.
Rotation
Applied to cropping, the practice of growing different crops on the same land
in a regular, recurring sequence. Rotation is adopted to hinder the development
or because of complement effects, or demands on the soil or for convenience of
spreading the times of peak labour demand.
Safener
A compound used in conjunction with a herbicide to provide extra
protection to the crop without reducing weed control. A safener usually
acts by increasing GSH and GST levels and activity.
Scarification
Scratching or changing the seed coat.
Seedling Growth Inhibitors
Mode of action of a group of herbicides that generally disrupt early
growth of plants.
Segregating Population
A collection of lines from a cross or population that is undergoing Mendelian or Hardy-Weinberg gene segregation.
Selection Pressure
The process that changes the relative frequency of one or more genes
within a population.
Selective
Herbicides which cause one species of plants to die, but another
species will survive the same treatment. Selectivity allows for acceptable weed
control without injury to crop plants.
Selectivity
Differential effect of a herbicide when applied to a mixed population
of plants; sensitive plants die, tolerant plants are unharmed. Implies that
different plant species do not respond in the same way to a particular
herbicide. Herbicides which cause one species of plants to die, but not
another, are selective. Selectivity allows for acceptable weed control without
injury to crop plants.
Selective
herbicide
Compounds that control weeds without adversely affecting the growth of a crop.
Selectivity may be due to differences in retention, uptake, movement,
metabolism or biochemical action of the herbicide in the crop and the weed.
Self
To induce pollination with pollen from the same plant.
Self-incompatible
The inability to produce seed by self-pollination.
Self-pollination
Pollination with pollen from the same flower or from other flowers of the same
plant.
Sensitivity
herbicide
Susceptibility of plants to effects of toxicant at low dosage; eg. many broad-leaf plants are sensitive to 2,4-D.
Sequential
application
Two or more herbicide treatments applied at different times to the same crop.
Sequencing
A means of identifying the order of nucleotides in DNA, RNA or amino acids in a
polypeptide.
Sexual
reproduction
Reproduction involving the union of gametes.
Shikimic acid
A crystalline acid C6H6 (OH)3COOH formed in plants as a precursor in the
biosynthesis of aromatic amino acids and of lignin.
Shikimate Pathway
Important chemical pathway in plants. It is responsible for producing
amino acids and other aromatic products.
Site of Absorption
Site of Absorption is the location where the herbicide is taken up by
the plant. This should not be confused with Site of Action which is the
biochemical pathway within the plant where the herbicide acts.
Site of action
In a biochemical pathway, the point at which a herbicide functions.
Site of Uptake
Site of Uptake is the location where the herbicide is taken up by the
plant. This should not be confused with Site of Action which is the biochemical
pathway within the plant where the herbicide acts.
Soil
incorporation
Mechanical mixing of herbicide with the soil.
Soil
persistence
Refers to the length of time that an herbicide applied to or in the soil
remains effective; to some degree phytotoxic to some
species.
Somaclonal variation
Somatic (vegetative non-sexual) plant cells can be propagated in vitro in an
appropriate nutrient medium. According to the composition and conditions the
cells may proliferate in an un-differentiated (disorganised)
pattern to form a callus or in a differentiated (organised)
manner to form a plant with a shoot and root. The cells which multiply by
division of the parent somatic cells are called somaclones and, theoretically, should be genetically identical with the parent. In fact in
vitro cell culture of somatic cells, whether from a leaf, a stem, a root, a
shoot or a cotyledon, frequently generates cells significantly different,
genetically, from the parent. During culture the DNA breaks up and is
reassembled in different sequences which give rise to plants different in identifiable
characters from the parent. Such progeny are called somaclonal variants and provide a useful source of genetic variation.
Somaclones
Plants produced by a genetic engineering technique by which single cells or
protoplasts are cultured to produce individuals which are genetically variable
from their genetically stable parent. The variation induced is called somaclonal.
Somatic
cell
Literally any cell from the 'soma' which includes all cells of an plant except
the germ cells. In some instances the term is used to describe
un-differentiated cells, such as those found in a cultured callus.
Somatic
embryogenesis
The generation from somatic cell or tissue culture of bipolar embryos, similar
to sexually derived embryos. Both sexual and somatic embryos possess a
primordial root and shoot.
Somatic hybridisation
The formation of hybrids by fusion of somatic cells, as opposed to the fusion
of gametes. The term is commonly applied to fusion of plant protoplasts.
Southern
blotting
This is a method for transferring separated DNA fragments from an agarose gel to a solid support such as a nitrocellulose
membrane.
Species
One kind of plant of animal. Abbreviated as sp. singular and spp. plural. Spp.
following genus name means that a number of species of that genus are
indicated. The fundamental category used in the taxonomic classification of
living organisms which ranks below genus. It is generally the final category
and is composed of individuals having common characteristics which distinguish
them from other categories.
Spectrophotometer
An instrument that analyses characteristics of organic compounds through
transmittance of light waves through solutions. Ultra-violet, and infra-red
wave lengths are commonly employed. Ordinary light can be used in certain types
of instruments, and electromagnetic fields are employed in some instruments.
Split
application
The total amount of a herbicide divided between two or more applications made
at different times to the same crop.
Stamen
The male part of a flower. It consists of an anther and a filament. Pollen is
produced in the anther.
Standard
deviation
The standard deviation of a set of n measurements x1, x2, x3, ..., xn is equal to the positive square root of the variance of
the measurements.
Standard
error
The precision of an estimator is measured by its standard deviation; hence, the
standard deviation of an estimator is called its standard error.
Stochastic
Affected by random variations; a stochastic variable can assume any one of a
set of values, each value having a certain probability. Contrast deterministic
where the state is known with certainly.
Stolon
A modified, creeping, above-ground stem capable of rooting and sending up new
shoots at its nodes, as in the strawberry plant.. Stolinferous;
bearing stolons or runners or shoots that take root.
Stomata
Small apertures (bounded by guard and accessory cells) in the surface of a leaf
or a young stem, opening or closing in response to light intensity, time of day
and other factors, adapted to control exchange of carbon dioxide, oxygen and
water vapour between active internal leaf cells and
the atmosphere for respiration and photosynthesis, singular. stoma.
Stratification
Exposing seeds to a cold period to encourage germination or break seed
dormancy;
Sulfonylureas
A herbicide family with similar chemical structure belonging to the
amino acid synthesis inhibitors mode of action; these herbicides specifically
target the ALS-AHAS enzyme.
Surfactant
An additive that reduces the surface tension ofa herbicide to allow for better contact between water droplet and plant surface;
cationic surfactants, ionic surfactants, nonionic surfactants; SURFace ACTive AgeNT.
Susceptibility
A plant's inability to withstand a herbicide at normal use rates.
Symplastic Path
Water travels from one cell to the next via plasmodesmata. Symplastic means "living" tissue.
Synergism
Increased phytotoxicity occurs when two or
more chemicals are applied together, as compared to the individual chemicals
applied alone.
Systemic
Having the ability to move throughout the plant by either the xylem or
phloem.
Systemic Herbicide
A herbicide that can move throughout the plant; the activity is not
limited to the point of application.
Tank mix
Two or more chemical herbicides or formulations mixed in the spray tank at the
time of spray application.
Target DNA
The particular portion of the template DNA which is copied during PCR.
Termination Sequence
The sequence of DNA which signals the transcription to stop.
Tetraploid
Having four times (4n) the basic number of chromosomes or twice the diploid
number (2n).
Threonine
Nonessential amino acid found in cheese, eggs, milk, meat, legumes,
nuts and seeds.
Thylakoid Membranes
A series of sealed membrane compartments found inside the chloroplast
of plant cells. The membranes contain the photosynthetic apparatus and all of
the chlorophyll in the leaf. Their structure as closed 'sacks' permits
functional 'inside' and 'outside' spaces within the chloroplast across which photophosphorylation can generate the proton gradient
necessary for ATP synthesis.
Tillage
The use of implements to cultivate the soil in the preparation of seed-beds and
root-beds for crops.
Tolerant
The inherent ability of a plant to survive and reproduce after
herbicide treatment. This implies that there was no selection or genetic
manipulation to make the plant tolerant; it is naturally tolerant.
Tonoplast
The vacuolar membrane in plant cells.
Trade Name
The name under which a product is marketed.
Trait
The characteristic that results from an expressing gene(s). Ex. Upright
leaves, drought tolerance, Bt resistance. A trait can be influenced by the
environment.
Transcription
The process by which the nucleotide sequence of DNA is copied into a
single-stranded molecule of RNA. The nucleotide sequence of the RNA created is
complementary to the DNA sequence except all thymine molecules are replaced
with uracil molecules.
Transfer RNA (t-RNA)
The RNA that carries amino acids to the ribosome to be placed in the sequence
prescribed by the messenger RNA.
Transformation
A genetic engineering procedure whereby a piece of foreign DNA is transferred
to a cell thus conferring upon it novel characters.
Transgenic Plant
A plant that has a new genetically engineered DNA sequence present in
every one of its cells. Genetically engineered plants are transgenic plants.
These two terms are used interchangeably.
Translation
The process following transcription during which the nucleotide
sequence of mRNA is read and 'translated' into a chain of amino acids
(protein). The mRNA sequence is read three nucleotides (codon)
at a time, and each codon codes for a specific amino
acid.
Translocation
Moving from one point to another within a plant by either the xylem or
phloem.
Transpiration
The loss of water as vapor from plants at their surfaces, primarily
through stomata.
Triazines
A family of herbicides with similar chemical structure and belonging to
the photosynthetic inhibitors mode of action.
Tyrosine
nonessential amino acid
Translation
The process during protein synthesis in which the genetic code in messenger RNA
is translated into the polypeptide sequence in protein.
Viability
The state of being alive. Capacity to germinate.
Uptake
The process of getting a herbicide from the outer surface of a plant to
the inside of the plant where the herbicide will either induce its herbicidal
activity or be translocated.
Vacuole
A membrane-bound (tonoplast) space larger
than a vesicle which stores material, either dissolved in water or as a
crystalline or flocculent mass. Vacuoles are key organelles for storage of
compounds and osmoregulation in plants.
Weed
An aggressive, invasive, easily dispersed nuisance plant, one which commonly
grows in cultivated ground to the detriment of a crop.
Weed control
The process of limiting weed infestations so that crops can be grown profitably
or other operations can be conducted efficiently.
Western Blot
A technique in which proteins are separated using electrophoresis and
transferred to a membrane so they can be identified and studied.
Xylem
The principal mineral and water-conducting tissues in vascular plants characterised by the pressure of tracheids.
May also contain vessels, parenchyma cells, fibres and sclerids.
Zygote
The cell resulting from the fusion of the male and female (haploid) gametes;
the fertilised ovum.