Which are the physiological effects of auxins on plants?

1. Apical dominance:

In a great majority of flowering plants, if the apical bud is intact, it suppresses the development of lateral buds. When the apical bud is removed, lateral buds become active. The phenomenon of suppres­sion of lateral buds, by apical bud is called apical dominance. It has been found out, that apical dominance is not due to the mere physical presence of the apical bud, but due to the production and transportation of auxins in/ from them. It has been reported that during their polar migration auxins pro­mote the production of axillary buds.

2. Cell division and cell elongation:

Auxins stimulate cell division in cam­bium and also in the primary meristems. Cell elongation brought about by additional production of wall materials (see mechanism of auxin action) is an important physiological role played by auxins. Another important charac­teristic of auxin is its differential action on shoot tip and root tip. While a higher auxin concentration promotes cell division at shoot tip, it actually inhibits cell division at root tip.

3. Root formation:

Auxins induce root formation at low concentrations. This is made use of by horticulturists to induce root formations in stem cut­tings. The concentration is very critical because a higher concentration in­hibits root growth.

4. Prevention of abscission layer:

Auxin prevents leaf fall by suppressing the formation of abscission layer.

5. Parthenocarpy:

Parthenocarpy or seedless formation of fruit is induced by auxins. Spraying of auxins on flowers induces parthenocarpic develop­ment of fruits in tomato, apples, cucumbers etc.

6. Xylem differentiation:

Axins can induce the differentiation of xylem vascular differentiation in callus, produced during grafting.

7. Miscellaneous activities:

Enzymes concerned with aspartic acid me­tabolism are activated by auxins, while the activity of the peroxidases is lowered. Floral inhibition is another auxin activity, but in pineapple auxin promotes flowering.