In this article we will discuss about:- 1. History of Abscisic Acid 2. Functions of Abscisic Acid 3. Uses.
History of Abscisic Acid:
It is also called stress hormone because the production of hormone is stimulated by drought, water logging and other adverse environmental conditions. Abscisic acid is known as dormin as it induces dormancy in buds, underground stems and seeds.
Its other names are abscissin II and inhibitor-B. Abscisic acid is a mildly acidic dextrorotatory cis sesquiterpene growth hormone which functions as a general growth inhibitor by counteracting other hormones (auxin, gibberellins, and cytokinins) or reactions mediated by them.
The hormone was first isolated by Addicott (1963) from Cotton bolls. It is produced in many parts of the plants but more abundantly inside the chloroplasts of green cells. The hormone is formed from mevalonic acid or xanthophyll. It is transported to all parts of the plant through diffusion as well as transport channels (phloem and xylem).
Functions of Abscisic Acid:
1. Bud Dormancy:
Abscisic acid induces dormancy of buds towards the approach of winter.
2. Seed Dormancy:
It is mainly caused by abscisic acid. Dormancy allows seeds to tolerate desiccation and extremes of temperature better. The buds as well as seeds sprout only when abscisic acid is overcome by gibberellins. Because of its action in inducing dormancy, abscisic acid or ABA is also named as dormin.
3. Stoppage of Cambium Activity:
Formation of abscisic acid stops mitosis in vascular cambium towards the approach of winter.
Abscisic acid promotes abscission of flowers and fruits.
5. Leaf Senescence:
Its excessive presence stops protein and RNA synthesis in the leaves and hence stimulates their senescence (leaf fall is actually promoted by ethylene).
During desiccation and other stresses, abscisic acid is rapidly synthesised. The inhibitor causes closure of stomata and hence prevents transpiration.
Abscisic acid increases resistance of plants to cold and other types of stresses. It is, therefore, also known as stress hormone.
8. Starch Hydrolysis:
Abscisic acid inhibits gibberellin mediated amylase formation during germination of cereal grains.
In small quantities, abscisic acid is known to promote flowering in some short day plants, e.g., Strawberry, Black Currant.
ABA has been found to induce parthenocarpic development in Rose.
Rooting of stem cuttings is promoted in some cases by abscisic acid, e.g., Bean, Ivy, Poinsettia (= Euphorbia pulcherrima).
12. Membrane Potential:
ABA induces a positive surface potential on cell membrane.
13. Controlled Growth:
It is antagonist to gibberellins and counteracts the effect of other growth promoting hormones (auxins and cytokinins) and therefore, keeps their activity under check. By controlling growth, ABA plays an important role in seed development and seed maturation. Normally it inhibits seed germination, growth of excised embryos, growth of Duckweed and other plants.
Uses of Abscisic Acid:
Application of minute quantity of abscisic acid to leaves shall reduce transpiration to a great extent through partial closure of stomata. It conserves water and reduces the requirement of irrigation. Photosynthesis is reduced to a lesser extent (Transpiration 56%: Photosynthesis 14%).
It is useful in introducing flowering in some short day plants kept under un-favourable photoperiods.
Use of abscisic acid promotes rooting in many stem cuttings.
Abscisic acid can be used in prolonging dormancy of buds, storage organs and seeds.