22. Gibberellic acid activates alpha-amylase activity in
(1) Endosperm        (2) Aleuronic layer
(3) Cotyledons        (4) Embryo

Correct answer: (2) Aleuronic (aleurone) layer

The plant growth regulator gibberellic acid (GA) activates alpha-amylase synthesis in the aleurone layer of cereal grains, not in the endosperm, cotyledons, or embryo. The aleurone cells then secrete alpha-amylase into the endosperm to hydrolyse stored starch into sugars for the developing embryo.

Option-wise explanation:

• (1) Endosperm: This tissue stores starch and proteins and is largely dead at maturity. It is the target that alpha-amylase acts on, but it is not where GA primarily induces alpha-amylase synthesis.

• (2) Aleuronic layer: Correct. Living aleurone cells surrounding the endosperm respond to GA by transcribing and secreting alpha-amylase and other hydrolases into the endosperm, enabling reserve mobilization.

• (3) Cotyledons: Important storage and photosynthetic organs in many dicots, but in cereal monocots like barley, cotyledons are not the main site of GA-induced alpha-amylase production.

• (4) Embryo: The embryo produces gibberellic acid, which then diffuses to the aleurone layer. It is the hormone source, not the principal tissue where alpha-amylase is induced and secreted.