What is a phytohormone? Name any two phytohormones.
Answers
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.