Plant growth hormones are set of biochemical secretions inside the plant and its parts which regulate the growth, enlargement, multiplication of the tissue and cells.
They control the rate and extent of plant growth starting from seed germination, after growth, flowering, fruit formation, ripening, wilting, falling of leaves etc.
Based on these facts modern scientists have developed synthetic plant growth hormones to increase the growth, flowering, fruit ripening etc for use in agriculture, horticulture, gardening.
The plant growth hormones are
- Absisic acid.
Auxin; They have a prominent role in entire growth of plant. They guide the seedling during germination of plant from seed stage in such a way that roots go into soil while stem moves up towards the sun. So auxin does it by phototropism (moving to light for stem) and geotropism (moving towards soil for roots) mechanism.
Further they promote plant elongation towards the sky and also towards the ground deeper by stem and roots respectively. This auxin is highly active in the tips of shoot (stem) and also root tip.
They induce cell elongation, inhibit falling of leaves and accelerate flower formation.
Gibberlin: These have a different role in promoting growth. They specially focus on elongating the nodes and also forming internodes. Nodes are those ridges or ring like structure seen on the stem of a bamboo, sugarcane etc. These gibberlins enhance elongation of a node and when the node is long enough they form an internode in between. Thus promote the growth of the plant.
They induce stem elongation, promote flowering, leaf expansion, seed germination etc.
Cytokines: The name comes from ability to divide cells. These participate in the growth of the plant by enhancing the cell multiplication. They increase the rate of cell division and mitosis in growing parts of the plant and hence promote profuse tissue formation necessary for growth. It has anti-auxin, anti-gibberlin property. Helps in conservation of water in plant during water deficiency.
Absicic acid: This hormone is a natural growth inhibitor. It has a role in some stage of plant growth like ripening of raw fruits etc. Thus they are involved in growth of plant to certain extent.
Ethylene: Ethylene is a gaseous phytohormone. It is also growth inhibitor like absicic acid. It is mainly involved in fruit maturation and ripening.
It also shows cell enlargement, geotropism, fruit ripening etc.
Tips to enhance plant growth hormones:
Plant growth hormones as shown above have diverse roles and some of them benefit yield in agriculture, flowering, fruiting etc. But the internal levels of hormones are always spontaneously controlled and depend on the season, fertility of soil, climate, genes and stages f growth. So to enhance these hormones scientists go for
♦Biotechnological modification of genes related to these hormones
♦External application of synthetic hormones.