Question

Plant hormone causing abscission of leaves, senescence, bud dormancy and inhibition of cell division is
A. IAA
B. Ethylene
C. Cytokinins
D. ABA

Answer 1

Plant hormones are small and signal molecules that are produced within plants. They present in the plants in extremely low concentrations. Plant hormones control the growth and development of the plant, also help in pathogen defence, stress tolerance, and reproductive development.

Complete step by step answer: Plant hormones are small, simple biochemical molecules. They are essential regulators of plant development which begin with seed germination. Plant hormones play an important role as a signalling molecule. It induces various responses related to plant stress. There are several plant hormones found and they are auxin, abscisic acid, ethylene, gibberellins, cytokinin, and salicylic acid. A wide range of actions has been performed by these plant hormones.
Shedding of leaves, flowers, and fruits are called abscission. It can be explained as the shedding away or cutting off of different parts of a plant. Generally, when a plant removes its leaves, flowers, or fruits, this condition is called abscission. During abscission, the colour of the leaves, flowers, and fruits changes. Plant hormone ABA or abscisic acid regulates the process of abscission. Auxin and cytokinin are responsible for the delay in abscission.
Senescence is a phase of the aging process in which the functional life of an organism terminates naturally is called senescence. Senescence does not occur in the whole plant. It takes place in a particular plant organ such as leaf and flowers or cells or cell organelles. Senescence is closely related to the phenomenon of aging. Senescence is promoted by hormones such as ABA or abscisic acid and ethylene.
Bud dormancy refers to the condition when growth, development, and other physical activity are stopped temporarily and growth can be reactivated. This bud dormancy is occurred due to the presence of plant hormone ABA or abscisic acid.
The growth of plants occurs by cell division followed by enlargement of the cells and increasing number of cells. Thus, the cell division is responsible for the growth of the plant and controls the growth of the plant. But sometimes cell division is inhibited and this is caused by the hormone ABA or abscisic acid. The plant hormone that results in the abscission of leaves, senescence, bud dormancy and inhibition of cell division is ABA or abscisic acid.
Therefore, the correct option is option D.

Note: The plant hormone is a small biochemical molecule present in plants and regulates the growth, development, stress, reproduction, etc. IAA is a form of auxin which controls the growth of the plant and prevents the abscission. Ethylene promotes cell division and senescence but cytokinin inhibits the senescence. ABA or abscisic acid promotes the abscission of leaves, senescence, bud dormancy and inhibition of cell division.