Abscisic acid

Abscisic acid:

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.


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