Question

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

[Review question: Pg. No: 241]

Answer 1

(a) Ethylene is a gaseous plant hormone. It is a growth inhibitor. The different actions of ethylene are as follows:

• Ethylene promotes the ripening of fruits, eg. Tomato, Apple, Mango, Banana and etc.
• Ethylene inhibits the elongation of stem and root in dicots.
• Ethylene hastens the senescence of leaves and flowers.
• Ethylene stimulates the formation of Abscission zone in leaves, flowers and fruits. This leads to premature shedding.
• 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 the tolerance of plants to various kinds of stress. So, it is also called a stress hormone.