Question

Give the example of plant hormones that promote growth and inhibit growth?

Answer 1

Hint: Plant hormones are signals produced within the plants. They control the plant growth and development. They occur in low concentrations. There are 5 classes of plant hormones providing different functions out of which auxin is one of the most important hormones.

Complete answer:
Plant hormones are organic compounds other than nutrients produced by them. They influence each and every activity of a plant from seed germination to plant senescence. They are also called phytohormones.
There are 5 classes of plant hormones. Each hormone performs its specific functions. They are:
> Auxins- It is the first group of plant hormones discovered. They are involved in the growth of a plant. Auxin is produced in the apex of the shoot, young leaves and fruits and prepared in cytosol of cells. It plays an important role in cell elongation, cell differentiation, flowering, parthenocarpic fruit development, etc.
> Gibberellins- They are also growth promoting hormones. They occur at low concentration in vegetative tissues but at higher concentrations in germinating seeds. They are produced in young leaves, roots, seeds, and fruits. Phloem is the most important transportation route for gibberellins. It also overcomes seed dormancy and helps in fruit enlargement. Plants with different sex male and female can be determined by GA.
> Cytokinins- They are classified as growth inhibiting hormones. Cytokinins stimulate cytokinesis (cell division). These hormones control leaf senescence and growth of lateral branches. They are synthesized in the meristematic region of the roots. They are transported via xylem and some also transport through phloem. The most naturally occurring cytokinin hormone is zeatin.
> Abscisic acid: It is also one the growth inhibiting hormones. Abscisic acid promotes seed dormancy, helps in closing stomata. They are also produced in response to stress. They transport through xylem and phloem. It plays a major role in seed dormancy.
> Ethylene- It is a gaseous plant hormone. It is also growth inhibiting hormones. It is important for fruit ripening, shoot growth, flowering, etc.
Therefore, the plant hormone that promotes growth is auxin and gibberellins and the plant hormones that inhibit growth are cytokinin, abscisic acid and ethylene.

Note: Ethylene is the only gaseous plant hormone.
Brassinosteroids are plant steroid hormones similar to animal steroids. They have a similar effect on a plant.