Question

Bring out the physiological effects of Auxin

Answer 1

Hint: The presence of growth regulating chemicals in plants was first suggested by Sachs in the latter half of the 19th century. The plant hormones act as messengers substances for growth regulation. These hormones are organic substances which are required in small action and at low concentration and their sites of action and synthesis are usually different. Most of the plant hormones represent broad action spectrum and thus hormones may influence several processes.
There are several plant hormones: Auxin, Gibberellins, Cytokinins, Ethylene, Abscisic acid. These plant regulators or hormones are also known as Phytohormones.

Complete answer:
Plant growth regulators include both endogenous and synthetic compounds. A particular hormone may promote certain physiological processes, inhibit some other and not affect many others. Developmental processes are regulated by growth regulators acting synergistically or antagonistically with one another.
Auxin is one of the most important groups of plant hormones. They were the first identified as a hormone. IAA (Indole acetic Acid) is the principal naturally occurring auxin found in all the plants including fungi.
The first indication about the existence of auxin was marked in the work of Charles Darwin in 1880, who was studying the bending of the Coleoptile of canary grass towards light.
The physiological effects of auxin include:
Cell division: It initiates as well as promotes cell division in tissues like Cambium.
Cell elongation: It causes the walls to become plastic and due to endosmosis, cell elongates.
Root formation: Auxin stimulates the formation of new roots.
Apical dominance: The auxin in the apical bud inhibits the growth of lateral buds and the phenomenon is called apical dominance.
Prevention of abscission layer: Another inhibitory effect of auxin is on the abscission of leaves and fruits which leads to leaf fall and fruit drop.

Note: The auxin hormone used in following ways in plants:
> Eradication of weeds
> Root Initiation
> Flower initiation
> Production of parthenocarpic fruit
> Apical dominance and dormancy
> Enzyme activity in plants
> To prevent premature fruit drop