what are the types of plant hormones??
Answers
The plants do not have a nervous system and sense organs like ear, nose,mouth,etc like the animals , but they can still sense things.
The plants coordinate their behavior against environmental changes by using hormones.
The functions of control and coordination in plants is performed by certain chemical substances.These chemical substances are called plant hormones or phytohormones.
There are four major types of plant hormones [phytohormones] . which are involved in the control and coordination in plants.These are :
1)Auxins
2)Gibberellins
3)Cutokinins
4)Abcisic acid
1)Auxins are the plant hormones which promote cell enlargement and cell differentiation. Auxins also promote fruit growth. Auxin hormone is responsible for phototropic and geotropic responses of plants.
2) Gibberellins are plant hormones which promote cell enlargement and cell differentiation in the presence of auxins. Gibberellins help in breaking the dormancy in seeds and buds. They also promote fruit growth. Gibberellins stimulates elongation of shoots of various plants
3) Cytokinins are plant hormones which promote cell division in plants.They also help in breaking the dormancy in seeds and buds. The delay the ageing of leaves.Cytokinins promote opening of stomata .
4)Abscisic acid (ABA) is a plant hormone which functions mainly as a growth inhibitor. Abscisic acid promotes the dormancy in seeds and buds [ this is the opposite of breaking the dormancy]. It also promotes closing of stomata. Abscisic acid promotes falling of leaves.
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.