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 Abscission from the plant tissue which could accelerate leaf fall.

• It was found that both dormin, Inhibitor B and Abscission Ii  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 gibbtelic acid aur kinetin.