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Structure of Abscissic Acid
History
Addicotetal (1963) found out that the shedding of cotton balls was due to a chemical substance Abscissin. Wareing and Cornforth isolated a substance that can induce bud dormancy. They named the substance as
dormin. Later it was found that the 2 chemicals were identical and were given the common name Abscissic acid.
Absicissic acid is a growth inhibitor which retards or suppresses growth and metabolism.
Physiological Effects of Absicissic Acid
Bud dormancy
It induces bud dormancy in a number of plants. In perennial plants, ABA causes the active axillary buds to become dormant.
Seed dormancy
ABA maintains dormancy in many seeds.
Cambium activity
ABA inhibits mitosis in vascular cambium.
Senescence
ABA accelerates senescence in leaves.
Control of transpiration
ABA functions as a stress hormone by inducing a temporary closure of stomata, to tide over adverse environmental conditions.
Abscission
ABA promotes abscission of leaves, flowers and fruits in most of the plants.

Separation Layer Shown as it is Just Beginning to Separate
Seed germination
ABA inhibits seed germination.
Cell division and cell elongation
ABA delays cell division and cell elongation.
Rooting
ABA promotes rooting of stem cuttings in some plants like ivy and bean.
Flowering
It inhibits flowering except in some short day plants where it promotes flowering.
Vitamins
Vitamins are biological products of plants. They also form a valuable part for the normal growth and development of organisms. Vitamins are mostly synthesised by plants and are stored in their various organs. They control important biochemical reaction in growth plants and animals.
Agricultural Applications of Abscissic Acid
Antitranspirants
Application of small quantities of ABA to the leaves reduces the rate of transpiration in a plant by bringing about closure of the stomata. So it is known as antitranspirant.
Other Uses
ABA is also used in inducing flowering in short day plants, rooting of stem cuttings and for inducing dormancy in buds and seeds.
Interaction Among Growth Regulators
Phytohormones do not act singly. They regulate plant developmental processes by acting synergistically or antagonistically.