Question

major hormone functions in plants..

Answer 1

Plant hormones (also known asphytohormones) are chemicals that regulateplant growth. In the United Kingdom, these are termed 'plant growth substances'.

Plant hormones are signal moleculesproduced within the plant, and occur in extremely low concentrations. Hormones regulate cellular processes in targeted cellslocally and, moved to other locations, in other functional parts of the plant. Hormones also determine the formation of flowers, stems,leaves, the shedding of leaves, and the development and ripening of fruit. Plants, unlike animals, lack glands that produce andsecrete hormones. Instead, each cell is capable of producing hormones. Plant hormones shape the plant, affecting seed growth, time of flowering, the sex of flowers,senescence of leaves, and fruits. They affect which tissues grow upward and which grow downward, leaf formation and stem growth, fruit development and ripening, plantlongevity, and even plant death. Hormones are vital to plant growth, and, lacking them, plants would be mostly a mass of undifferentiated cells. So they are also known as growth factors or growth hormones. The term 'Phytohormone' was coined by Thimannin 1948[clarification needed].

Phytohormones are found not only in higher plants, but in algae too, showing similar functions,[1] and in microorganisms, like fungiand bacteria, but, in this case, they play no hormonal or other immediate physiological role in the producing organism and can, thus, be regarded as secondary metabolites.[2]

Answer 2

Types of Phytohormones.

The major types of plant hormones which are involved in the control and coordination in plants are as follows:

(i) Auxins are the group of plant hormones synthesised at the shoot-tip of the plant body .

• It promotes cell elongation, root formation, cell division, respiration and other physiological processes like protein synthesis, water uptake and protoplasmic permeability.

• Auxins also play an important role in the development of seedless fruits.

(ii) Gibberellins stimulate stem elongation, seed gennination and flowering.

• The maximum concentration of gibberellins is found in fruits and seeds.

(iii) Cytokinins are produced in dividing cells throughout the plant

• In mature plants, cytokinins are produced in the root tips and are transported to the shoots.

• Cytokinins promote cell division and also helps in breaking the dormacy of seeds and buds and regulate the phloem transport.

• Cytokinins delay the ageing in leaves and promote the opening of stomata.

(iv) Abscisic Acid (ABA) : It is a growth inhibitor which reverses the growth-promoting effects of auxins and gibberellins.

Its effect include wilting of leaves.

• It causes dormancy of seeds, tubers and bulbs.

• It promotes the closing of stomata and is responsible for the loss of RNA, proteins and chlorophylls.