Explanation
$$\textbf{Correct option: }$$ D
$$\textbf{ Solution: }$$
$$\textbf{ Option (d): }$$
$$\bullet$$ Cytokinins are the plant hormone that promotes the growth of the plant.
$$\bullet$$ Cytokinins promote the ageing of leaves (delay senescence) and also help in breaking the dormancy of seeds and buds.
$$\bullet$$ Auxin is produced by the cells present on the tip of the stems and roots. This tip of the stem is composed of cells of apical meristem which produces auxin hormone.
$$\bullet$$ The bending of the stem of plants towards light is promoted by auxin which is a plant growth hormone.
$$\bullet$$ Gibberellins are especially useful in enhancing seed germination.
$$\bullet$$ Ethylene is responsible for the immature falling of leaves.
Hence, the correct option is (d).
Gibberellins are plant hormones that regulate growth and influence various developmental processes, including stem elongation, germination, dormancy, flowering, sex expression, enzyme induction and leaf and fruit senescence. Gibberellin was first recognized in 1926 by a Japanese scientist, Elichi Kurosawa studying bakane, the 'foolish seedling disease' in rice. It was first isolated in 1935 by Teijiro Yabuta and Sumuki from fungal strains provided by Kurosawa from Gibberella fujikori. Yabuta named the isolate as gibberellin.
The substrate for α-amylase is stored starch and the end product is free sugar, which is needed for the growth of emerging embryo. After imbibition α-amylase begins in the aleurone layer by the De novo pathway. If the embryo of the seed is removed prior to inbibition, however, no increase in α-amylase activity occurs, suggesting that a hormone or plant growth substance produced by the embryo is necessary for the synthesis of α-amylase. The plant growth hormone gibberellic acid (GA) is the messenger that triggers this response. GA is produced in the embryo and migrates to the aleurone layer, where the synthesis of α-amylase is stimulated.
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