Abscissic Acid (ABA)

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.