Auxin and Auxinic Herbicide Mechanism(s) of Action - Part 1 - Introduction Glossary

ACC oxidase

The enzyme in the ethylene biosynthesis pathway converting ACC (1-aminocyclopropane-1-carboxylic acid) to ethylene.

ACC synthase

The enzyme in the ethylene biosynthesis pathway converting SAM (S-adenosyl-methionine) to ACC (1-aminocyclopropane-1-carboxylic acid).


Having a pH lower than 7, having a higher concentration of H+ ions.


A negatively charged ion.


Adenosine 5'-triphosphate


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.

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.


Unidirectional transport from the apex to the base.


A mass of undifferentiated cells used in tissue culture.

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.


The tissue in roots and stems lying between the epidermis and the vascular tissues.


A compartment in a plant or animal cell surrounding the nucleus in which many cell organelles and molecules are suspended.


The liquid substance of protoplasm, excluding all the organelles such as nuclei, plastids, ribosomes.


A subclass of of Angiosperms.

They tend to have:
-broad leaves
-two cotyledons
-netlike veins in the leaves
-flower parts are usually in fours or fives
-a ring of primary vascular bundles in the stem
-taproot system

ex. most trees and shrubs, broadleafs


Process whereby molecules move from areas of higher concentration to areas of lower concentration.


The release of a proton from a molecule due to a change in pH.


(deoxyribonucleic acid) The molecule that encodes genetic information. DNA is a double-stranded molecule held together by weak bonds between base pairs of nucleotides. It is the fundamental substance of which genes are composed.


Movement from the cytoplasm to the cell wall region; out of the cell.


Special protein molecules which function in catalyzing chemical reactions.


The downward curvature of leaves that occurs when the upper side of the petiole grows faster than the lower side.


A plant hormone produced by most plant tissues involved in fruit ripening, seed germination, senescence, abscission, and other aspects of plant development.


Applied externally; not from within the organism.


A special class of wall-loosening proteins which cause cell wall expansion by loosening the hydrogen bonding between wall polysaccharides.

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).


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.


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.


A pesticide used to kill plants.


The reaction of a substance with water.


A chemical reaction in which some reactant combines with water and splits the water into hydrogen and hydroxyl ions.


Water "fearing"; compounds that are relatively insoluble in water and other polar solvents and soluble in lipids and other nonpolar solvents.


Movement from the cell wall region into the cytoplasm; into of the cell.


Molecules with a positive or negative charge.


Having chemical properties relating to lipids (lipid-like), nonpolar compounds that are highly soluble in organic solvents, but not water; hydrophobic.


A general term referring to the change of a herbicide from an active to an inactive state.


An essential amino acid found in cereal, whole grains, sesame and sunflower seeds, and yeast.

mode of action

How a herbicide affects a plant including uptake, translocation and general effect on a plant.


A subclass of Angiosperm plants based on anatomical characteristics.
They tend to have:

-Narrow leaves
-One cotyledon
-Parallel veins in the leaves
-Flower parts are usually in multiples of threes
-A scattered arrangement of primary vascular bundles in the stem
-Fibrous root system

ex. grass, daylilies, corn


A joint on a stem where shoots, leaves and flowers arise.


A sequence of interconnecting enzyme reactions.


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.


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.


Phospholipids containing inositol involved in linking extracellular signals to intracellular responses, or signal transduction.


The process in which plants use light energy to make sugars and other organic food molecules from carbon dioxide and water.


A substance which is toxic to plants.

plasma membrane

The semi-permeable membrane that surrounds the protoplasm of a cell.


More hydrophilic or water loving.


Application of a herbicide after the plant has emerged.

protein kinases

Enzymes that phosphorylate proteins using ATP.


A positively-charged atomic particle; a hydrogen ion H+.


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.

secondary messengers

Transient secondary signals inside the cell that greatly amplify the original signal.


A herbicide that is toxic to certain plants but harmless to others.


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.


Portion of the developing seedling above the root system.


A fundamental category of taxonomic classification, ranking below a genus or subgenus and consisting of related organisms capable of interbreeding.


Bears the buds, leaves and flowers of a plant.


An opening in the outer layer cells in a leaf bordered by two guard cells and serving in gas exchange.


The inability to survive a herbicide at its use rate.


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.


The vacuolar membrane in plant cells.


Moving from one point to another within a plant by either the xylem or phloem.

turgor pressure

The positive pressure built up when water is compressed.


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.

vascular cambium

A layer of meristematic cells located between xylem and phloem tissues which divide to give off cells toward both tissues. This process forms secondary growth in stems and roots in broadleaf plants.


Liquids or solids with relatively high vapor pressure at normal temperatures. The higher the vapor pressure, the more likely the substance will vaporize into a gas.

water potential

The chemical potential of water; a measure of the ability of a substance to absorb or release water relative to another substance.


Nonliving cells connected end to end to form a series of long, thin tubes from root to the shoot, used to supply cells with water and nutrients that are dissolved in water.