ROLE OF PHYTOHORMONES- ABA

Phytohormones

    Abscisic Acid
    • Abscisic acid (ABA) is a hormone that functions by inhibiting growth activities in times of environmental stress rather than by promoting growth.
    • It often serves as an antagonist to the other growth promoting hormones in plant.
    • ABA which is also synthesized from mevalonic acid, got its name from erroneous belief that it promoted the formation of abscission layers in leaves and fruits.
    • It does not, although leaf abscission accompanies dormancy in many plants
    Nature of Abscisic Acid
    • Abscisic acid is a single compound unlike the auxins, gibberellins, and cytokinins.
    • It was called "abscisin II" originally because it was thought to play a major role in abscission of fruits.
    • At about the same time another group was calling it "dormin" because they thought it had a major role in bud dormancy.
    • The name abscisic acid (ABA) was coined by a compromise between the two groups.
    • Though ABA generally is thought to play mostly inhibitory roles, it has many promoting functions as well

    Functions of Abscisic Acid
    The following are some of the physiological responses known to be associated with abscisic acid
    • Stimulates the closure of stomata (water stress brings about an increase in ABA synthesis).
    • Inhibits shoot growth but will not have as much affect on roots or may even promote growth of roots.
    • Induces seeds to synthesize storage proteins.
    • Inhibits the affect of gibberellins on stimulating de novo synthesis of a-amylase.
    • Has some effect on induction and maintenance of dormancy.
    • Induces gene transcription especially for proteinase inhibitors in response to wounding which may explain an apparent role in pathogen defense.

Last modified: Tuesday, 26 June 2012, 5:12 AM