AuxinPromote flowering in plants like pineapple.

Help to initiate rooting in stem cuttings.

Prevent dropping of fruits and leaves too early.

Promote natural detachment (abscission) of older leaves and fruits.

Control xylem differentiation and help in cell division.

Gibberellins

Increase the axis length in plants such as grape stalks.

Delay senescence (i.e. ageing) in fruits. As a result, their market period is extended.

Help fruits like apples to elongate and improve their shape.

Functions of Abscisic Acid:

1. Bud Dormancy:

Abscisic acid induces dormancy of buds towards the approach of winter.

. Seed Dormancy:

It is mainly caused by abscisic acid. Dormancy allows seeds to tolerate desiccation and extremes of temperature better. The buds as well as seeds sprout only when abscisic acid is overcome by gibberellins. Because of its action in inducing dormancy, abscisic acid or ABA is also named as dormin.

3. Stoppage of Cambium Activity:

Formation of abscisic acid stops mitosis in vascu­lar cambium towards the approach of winter.

4. Abscission:

Abscisic acid promotes abscission of flowers and fruits.

5. Leaf Senescence:

Its excessive presence stops protein and RNA synthesis in the leaves and hence stimulates their senescence (leaf fall is actually promoted by ethylene).