Growth Regulators & Their Effects in Crop Plants

CHAPTER: 15(A)

Growth Regulators & Their Effects in Crop Plants

Growth Regulators & Phytohormones:

Ø  There is a complex series of events like fertilization, flowering, growing, which leads to a mature plant. These events are collectively called as development. This development is a process regulated by specific mobile chemical agents called growth regulators or growth substancs.

Ø  Sometimes, the term growth hormone (Phytohormone) is misused with growth regulator. The definition of phytohormone is “An organic substance produced naturally in plants controlling growth and other functions at a site remote from its place of production and active in minute amounts.”

Ø  According to K.V. Thiamann, whereas growth regulators include all naturally occurring as well as synthetic substance which control growth. As the above given definition indicates, all phytohormones are growth regulators but all growth regulators are not phytohormones.

Ø  Growth regulators are either growth promoters or growth inhibitors. Growth Promoters are- Auxins, Gibberellins, Cytokinins, and Growth inhibitors are- Absecisic acid & Ethylene.

What is the difference between Plant Hormones and Animal Hormones?

1. Plant hormones are simple organic substances and animal hormones are complex organic substances.
2. Plant hormones are transported through xylem, phloem or by diffusion and animal hormones are transported in the blood.
3. There are no specific organs involved in the synthesis of the plant hormones, whereas animal hormones are always synthesized in endocrine glands.

The major classes of planthormones are:

1.      Auxin

2.      Cytokinins

3.      Gibberellins

4.      Abscisic Acid

5.      Ehylene

These hormones are promoters and inhibitors. Auxin, cytokinins, and gibberellins are growth promoters where as abscissic acid and ethylene are growth inhibitors. These hormones help plant for their growth, flowering, fruiting, and reproduction. Among these hormones auxin was first discovered as plant hormones. Ethylene is considered as exogenous hormones and helps in the ripening of the fruits.