Certain plants possess a type of hormone which acts as growth inhibitor. Abscissic acid (also known as dormin) is a naturally occurring growth regulator found in a wide variety of plants. It is a very powerful growth inhibitor.
It was discovered in 1963 by Addicott ct al. It opposes the action of auxins, gibberellins and cytokinins within plant body. Abscissic acid is mostly produced in mature seeds and is translocated through phloem and xylem to shoot tips and roots. Abscissic acid has following functions in plant life.
(1) It induces dormancy in buds and seeds.
(2) It promotes senescence of leaves, appearance of abscission layer, leaf fall and ageing.
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(3) It inhibits gibberellin induced growth in various plants and is known to be a prowerful gibberellin antagoniser.
(4) It brings about quick stomatal closure.
(5) It regulates the growth and ripening of fruits.
(6) It is responsible for geotropism of roots.