(a) Name the gaseous plant hormone. Describe its three different actions in plants.
(b) Which hormone is known as stress hormone in plants ? Why?

Explanation

(a) Ethylene is a gaseous plant hormone. It is a growth inhibitor. The different actions of ethylene are as follows:
(i ) Ethylene promotes the ripening of fruits, eg. Tomato, Apple, Mango, Banana and etc.
(ii) Ethylene inhibits the elongation of stem and root in dicots.
(iii) Ethylene hastens the senescence of leaves and flowers.
(iv) Ethylene stimulates formation of Abscission zone in leaves, flowers and fruits. This leads to premature shedding.
(v) Ethylene breaks the dormancy of buds, seeds and storage organs.
(b) Abscisic acid (ABA) is a growth inhibitor which regulates abscission and dormancy. It increases tolerance of plants to various kinds of stress. So, it is also called as stress hormone.