Abscisic acid (ABA) is a growth inhibitor.
- Discovered by 3 independent researchers as inhibitor-B, abscission II & dormin.They were chemically identical.
- Addicott isolated it from cotton balls. Later renamed as abscisic acid.
- Site of synthesis: chloroplast in leaves.
- Translocated through phloem.
- Formed by oxidation of carotenoids.
Physiological effects of abscisic acid:
- It induces bud dormancy thus preventing the premature growth of buds during winter.
- It induces seed dormancy playing an important role in seed development & maturation.
- Inhibits seed germination thus, allowing seeds to tolerate desiccation & extremes of temperature.
- Causes abscission of flowers & fruits.
- Can cause senescence of leaves.
- It is an inhibitor of plant growth and metabolism. Inhibits shoot growth by inhibiting cell division & cell elongation. Has no effect on root growth.
- It acts as a stress hormone. Ethylene is produced in wilting leaves that causes partial closure of stomata by interfering in the uptake of K+ ions by the guard cells. Thus, decreasing the rate of transpiration. Hence it is also referred as anti-transpirant.
- It is an anti-gibberellin: as it is an antagonist to gibberellins and inhibits gibberellins induced growth.