21 .During germination of barley seeds, enzymes for mobilization of reserve material to developing embryo are secreted from
(1) Endosperm        (2) Embryo
(3) Aleurone layer   (4) Embryonic leaves

Concept in one line

In germinating barley (a cereal monocot), most of the hydrolytic enzymes that mobilize reserves for the embryo (like α‑amylase, proteases, β‑glucanases) are synthesized and secreted mainly by the aleurone layer, under the signal of gibberellin released from the embryo.

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Option-by-option explanation

(1) Endosperm

The endosperm is primarily a storage tissue packed with starch and proteins.

• In mature barley grain it is largely dead; it does not actively synthesize and secrete enzymes.

• Instead, it is the substrate that enzymes act upon.
  Therefore, it is not the main source of the digestive enzymes.

(2) Embryo

The embryo is the living future plant and the source of gibberellic acid (GA) during germination.

• GA diffuses from the embryo to the aleurone layer.

• Although some enzymes exist in the embryo, the bulk of reserve‑mobilizing enzymes for endosperm degradation are not secreted from here.

(3) Aleurone layer – correct answer

The aleurone is a one‑ to few‑cell‑thick living layer around the endosperm.

• GA from the embryo induces aleurone cells to transcribe, synthesize, and secrete α‑amylase, proteases, and other hydrolases into the endosperm.

• These enzymes digest starch and storage proteins, releasing sugars and amino acids that move back to the embryo for growth.
  Hence, the key enzyme‑secreting tissue in barley germination is the aleurone layer.

(4) Embryonic leaves

Embryonic leaves (plumule) are part of the embryo that will later develop into the shoot system.

• At early germination they mainly grow using food delivered from the endosperm; they do not secrete the bulk of hydrolytic enzymes into the endosperm.