The plant growth regulators are simple organic molecules having several chemical compositions. They are also described as phytohormones or plant hormones.
These plant growth regulators are divided into two major groups –
- Auxins, Gibberellins, and Cytokinins are grouped into Plant growth promoters
- Abscisic acid and Ethylene are grouped into Plant growth inhibitors.
Ethylene may fit in either of these groups.
Let us study about Plant Growth Regulators in detail.
Plant Growth Promoters
The term is applied to indole-3-acetic acid and other related compounds. Auxins 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. Auxins are mainly involved in the initiation of roots, in stem cuttings, promote flowering, and prevent dropping of fruits and leaves at early stages. Apical dominance may occur in which the growth of lateral buds is inhibited by the growth of apical buds. In such cases, the shoot caps may be removed. They are used as herbicides to kill dicot weeds and help in cell division.
The first gibberellin to be discovered was gibberellic acid. Now there are more than 100 types of gibberellins. They are acidic and help in increasing the height of plants, increase in the length of certain plants like sugarcane and also involved in increasing its yield. Gibberellins also delay aging.
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.
Plant Growth Inhibitors
It regulates abscission and dormancy. It inhibits plant metabolism and seed germination. Due to its stimulation, closure of stomata may occur and tolerance of plants to various kinds of stresses increases. Therefore, it is also known as the stress hormone.
A plant growth regulator which can be used as both plant growth promoters and plant growth inhibitors. Ethylene is synthesized by the ripening fruits and aging tissues. It promotes abscission and senescence of leaves and flowers. It also breaks the dormancy of seeds and buds. The most widely used plant growth regulator in agriculture is ethylene. We can add this to fruits in order to hasten their ripening process.
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