The Abscisic Acid - Discovey, Function and role as plant growth regulator.

During the course of their study on bud dormancy in woody  plants P. F. Wareing isolated a dormancy inducing substance from the leaves of Ãcer  pseudo  platanus  and they called it dormin.

Abscisic Acid  is a natural growth regulator regulating substance which act as a growth inhibitor at a very low concentration.

At the same time H. R.  Carns and Addicot also isolated a substance Abscisin from the plant tissue which could accelerate leaf fall. It was found that both dormin and Abscisin  are chemically the same compound and they were named as abscisic acid. 

This plant growth regulator occurs widely in plant Kingdom. Its presence  has been detected in a variety of plant organs such as stem  leaves, bud  fruit and seed. It is synthesised predominantly in mature leaves and then transported to stem Apices.

The Abscisic Acid Consists of 15 carbon atoms; it has a six-carbon  ring structure to which a side chain is attached.

The Abscisic Acid acts on the growing system by inhibiting both cell division and cell extension. It also affects the synthesis of Nucleic acid  and protein synthesis. It stimulates the production of hydrolytic enzymes and inhibits  the biosynthesis of various growth hormones. It also inhibit the action of gibberellic acid to promote dormancy

👌👌Remember It also stimulates the closure of stomata and increases the tolerance of plants to various kinds of stresses therefore it is called a stress hormone. 

But Dormancy  refers to the stop of growth of shoot apical buds under environmental condition. The Abscisic Acid is an important dormancy regulating hormone.  It delays  or stops the opening of both vegetative and flowering buds. 

Environmental conditions which favour dormancy cause accumulation of the abscisic acid  and decrease the  gibberellic acid content. Therefore the  bud dormancy is  regulated by a balance between gibberellic acid and  Abscisic Acid.

The initial phase of plant response to the low temperature is closely associated with the onset of winter dormancy. Abscisic Acid acts as a hardiness promoter in several trees. The Abscisic Acid is a strong germination inhibitor. Concentration of Abscisic acid required to bring about an inhibitory effect depending upon the species. The Abscisic  acid interacts with the gibberellic acid and the kinetin during the germinating activities. 

The role of The Abscisic Acid in the development of fruit is not certain it promotes the development of parthenocarpic fruit. In pear and Grape, the endogenous content of Acetic Acid gradually increases with the development of the fruit till the onset of ripening process. 

 The Abscisic Acid  increases senescence  and abscission of the leaf and other plant organs; this is accompanied by Rapid loss of chlorophyll protein and RNA molecule. The effect of Abscisic Acid on senescence  is partially reverse by the application of gibberellic acid aur kinetin.