Give a brief account on Programmed Cell Death (PCD).

Explanation

(1) Old age is called senescence in plants.
(2) Senescence is controlled by plants own genetic programme and death of the plant or plant part consequent to senescence is called Programmed Cell Death.
(3) In short senescence of an individual cell is called PCD.

(4) The proteolytic enzymes involving PCD in plants are phytaspases and in animals are caspases.
(5) The nutrients and other substrates from senescing cells and tissues are remobilized and reallocated to other parts of the plant that survives.
(6) The protoplasts of devloping xylem vessels and tracheids die and disappear at maturity to make them functionally efficient to conduct water for transport.
(7) In aquatic plants, aerenchyma is normally formed in different parts of the plant such as roots and stems which encloses large air spaces that are created through PCD.
(8) In the development of unisexual flowers, male and female are present in earlier stages, but only one of these two completes its devlopment while other aborts through PCD.