As the plants require oxygen, water, sunlight, and nutrition to grow and develop, they do require certain chemical substances to manage their growth and development. These chemicals substances are called Plant Growth Regulators and are produced naturally by the plants itself.
The plant growth regulators are simple organic molecules having several chemical compositions. They are also described as phytohormones, plant growth substances, or plant hormones.
Based on their action, plant growth regulators are broadly classified into two major groups: Plant growth promoters and Plant growth inhibitors.
Auxins, Gibberellins, and Cytokinins are grouped into Plant growth promoters and Abscisic acid and Ethylene are grouped into Plant growth inhibitors.
Note: Ethylene can be grouped either into the promoters or into the plant inhibitors.
Let us study more in detail about the Plant Growth Regulators.
Plant Growth Promoters
The first phytohormones to be discovered is the Auxin and it was discovered by the biologist Charles Darwin.
Auxins are one of the most important plant hormones and the chief naturally occurring auxin is indole-3 acetic acid – IAA and other related compounds. The term Auxins is derived from the Greek language meaning to grow.
These plant growth regulators are generally produced at the points of stems and roots from where they are transported other parts of the plants. These plant hormones include both natural and synthetic sources. Indole-3-acetic acid and indole butyric acid are obtained from natural plants sources, whereas naphthalene acetic acid and 2, 4-dichlorophenoxyacetic acid are obtained from synthetic sources.
Functions of Auxins
Gibberellins are an extensive chemical family based on the ent-gibberellane structure. The first gibberellin to be discovered was gibberellic acid. Now there are more than 100 types of gibberellins and are mainly obtained from a variety of organisms from fungi to higher plants.
They are acidic and are denoted as follows – GA1, GA2, GA3etc. GA3
Functions of Gibberellins
These are produced in the regions where cell division occurs; mostly in the roots and shoots. They help in the production of new leaves, lateral shoot growth, chloroplasts in leaves etc. They help in overcoming apical dominance and delay aging of leaves.
Functions of Cytokinins
Plant Growth Inhibitors
It is a growth inhibitor which was discovered in the 1960s. It was initially called dormant. Later another compound abscisin-II was discovered and are commonly called as abscisic acid. This growth inhibitor is synthesized within the stem, leaves, fruits, and seeds of the plant. Abscisic acid mostly acts as an antagonist to Gibberellic acid. It is also known as the stress hormone as it helps by increasing the tolerance of plants to different kinds of stress.
Functions of Abscisic acid
Ethylene is a simple, gaseous plant growth regulator, synthesis by most of the plant organs including ripening fruits and aging tissues. It is an unsaturated hydrocarbon having double covalent bonds between and adjacent to carbon atoms.
Ethylene is used as both plant growth promoters and plant growth inhibitors. Ethylene is synthesized by the ripening fruits and aging tissues.
Functions of Ethylene
Ethylene is the most widely used plant growth regulator as it helps in regulating many physiological processes.
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