Describe physiological effect of plant growth …

Auxins

• IAA and indole butyric acid (IBA) have been isolated from plants and NAA (naphthalene acetic acid) and 2, 4-D (2, 4-dichlorophenoxyacetic) are synthetic auxins.
• They help to initiate rooting in stem cuttings, promote flowering, prevent fruit and leaf drop at early stages, induce parthenocarpy (example- tomato).
• In most higher plants, the growing apical bud inhibits the growth of the lateral (axillary) buds, a phenomenon called apical dominance.
• Auxins are widely used as herbicides.

Example- 2, 4-D is widely used to kill dicotyledonous weeds.

Gibberellins

• Gibberellins are denoted as GA₁, GA₂, GA₃.
• All gibberellins are acidic.
• They help to increase in length of axis, elongate and improve shape of fruits, delay senescence,
• Spraying juvenile conifers with GAs hastens the maturity period, thus leading to early seed production.
• Gibberellins also promotes bolting, defined as internode elongation just prior to flowering, in beet, cabbages.

Cytokinins

• Cytokinins were discovered as kinetin from the autoclaved herring sperm DNA.
• Natural cytokinins are synthesised in regions where rapid cell division occurs, for example, root apices.