Question

Leaf fall occurs when the content of
(a) auxin increases
(b) auxin decreases
(c) abscisic acid decreases
(d) gibberellic acid decreases

Answer 1

Leaf fall occurs when the content of auxin decreases.

• Option (b) is correct.
• Leaf fall occurs when the content of auxin in lamina is lower when compared to the stem.

• And even there will be increased content of ethylene in the lamina during abscission (separation of leaves).
• The main reason is the photosynthesis reduction.

Answer 2

Leaf fall occurs when the content of  auxin decreases.

Option (B) is correct.

Explanation:

• The detachment or fall of older leaves is known as Leaf abscission.
• It takes place at the base of the petiole.
• The base of petiole of young leaf synthesizes auxin, therefore it is observed that the leaf at the origin of petiole does not fall off.
• During leaf fall season, the amount of auxin is low in the lamina as compared to stem.
• Also, ethylene content is high in the lamina during abscission.

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