Question

What are the physiological processes which are regulated by ethylene in plants?

Answer 1

Phytohormones or plant hormones are organic substances which help in the regulation of plant growth and development. Plants produce a variety of hormones, including auxin, gibberellin (GA), abscisic acid (ABA), cytokinin (CK), and salicylic acid (SA), ethylene (ET), jasmonic acid (JA), brassinosteroid (BR) and peptides. Absence of these hormones leads to negative impacts on plant growth.

Complete answer:
Ethylene is known to regulate many important physiological processes in plants some of them are enlisted below:
Inhibition of stem and root elongation: In many dicot plants it has been found that ethylene inhibits elongation of roots and stems, which also leads to radial growth of stem and roots thus thickening them.
Senescence: Ethylene leads to early drop (abscission) of leaves, flowers and fruits. Moreover, it also prevents bud opening if present in excess.
Flowering: In certain plants like pineapple, it promotes flowering.
Fruit ripening: At appropriate climatic conditions ethylene is known to induce ripening of fruits and dropping of dry fruits. Commercially, ethylene is used for the artificial ripening of fruits like apple, citrus, mud apples, custard apples etc.
Sprouting of storage organs: Some vegetative plant parts can be induced to sprout on application with ethylene.

Note:
Plants make ethylene from the amino acid methionine. It is formed in almost all parts of plants: roots, leaves, flowers, seeds, fruits. The greatest synthesis occurs during the ripening of fruits. Excessive auxin can also elicit ethylene synthesis, and many of the effects of excess auxin are actually produced by ethylene. It is a gaseous hormone.