15. Mobilization of starch by alpha amylase activity is induced by

(1) Auxin                         (2) Cytokinin
(3) Gibberellic acid            (4) Ethylene

Correct answer: (3) Gibberellic acid.

Gibberellic acid (GA) stimulates the synthesis and secretion of α-amylase in the aleurone layer of cereal grains, which then hydrolyses starch in the endosperm to soluble sugars. These sugars fuel embryo growth and seedling establishment, so “mobilization of starch by alpha amylase activity” is classically attributed to GA.

Explanation of options:

• (1) Auxin – regulates cell elongation, apical dominance, and differentiation, but is not the primary hormone inducing α-amylase for starch mobilization in seeds.

• (2) Cytokinin – promotes cell division and delays senescence; it does not have the key role in α-amylase–mediated starch breakdown during germination.

• (3) Gibberellic acid – correct; GA from the embryo signals aleurone cells to produce α-amylase, initiating rapid starch degradation into maltose and glucose.

• (4) Ethylene – involved in fruit ripening, abscission, and some stress responses, not in the classic GA–α-amylase pathway for starch mobilization.