Plant Hormones: Ethylene

CHAPTER: 15(E)

Plant Hormones: Ethylene

Ethylene:       

•      The gas ethylene is also known to function as growth hormone.

•      Earlier it was considered to be exogenous substances which regulate a large number of physiological processes in plants but now it has been kept under the categories of plant hormones.

•      This is only gaseous hormones of plants known.

•      Ethylene is actually a natural product of ripening fruit. It is most powerful ripening hormone present in small quantity in plant tissues.

•      Ethylene is produced by fruits, flowers, seeds, leaves and roots.

•      Its chemical formula is CH₂ = CH₂ .

Biosynthesis of Ethylene:

•      Ethylene is produced from essentially all parts of higher plants, including leaves, stems, roots, flowers, fruits, tubers, and seeds. Ethylene production is regulated by a variety of developmental and environmental factors. During the life of the plant, ethylene production is induced during certain stages of growth such as germination, ripening of fruits, abscission of leaves, and senescence of flowers.

•      Ethylene production can also be induced by a variety of external aspects such as mechanical wounding, environmental stresses, and certain chemicals including auxin and other regulators.

•      Ethylene is biosynthesized from the amino acid methionine to S-adenosyl-Lmethionine (SAM, also called Adomet) by the enzyme Met Adenosyltransferase.

•      SAM is then converted to 1-aminocyclopropane-1-carboxylic acid (ACC) by the enzyme ACC synthase (ACS).

•      The activity of ACS determines the rate of ethylene production, therefore regulation of this enzyme is key factor for the ethylene biosynthesis.

•      The final step requires oxygen and involves the action of the enzyme ACC-oxidase (ACO), formerly known as the ethylene forming enzyme (EFE). 

Physiological roles of Ethylene:

•      Activate malic enzyme, pyruvate decarboxylase and breaking down protein in ripening.

•      Accelerates the abscission layer.

•      Help in RNA and DNA synthesis.

•      Responsible for epinastic and tropic movement

•      Prevent elongation of root and stem in longitudinal direction.

Practical Application of Ethylene:

•      It is used for synthesized flowering and accelerate the ripening of fruits like pineapple, banana, mango etc.

•      Breaks the dormancy.

•      Reduce the incidence of insect and pest diseases.

•      Increase the no. of male flowers.

•      Helps in degreening of many fruits.

•      Stimulates isodiametric growth of root and stem.