Hormones in plants with definition and function
Answers
Auxin helps in cell enlargement by increasing the plasticity of the cell wall.
Auxin helps in promoting the growth of the plant’s tissue.
Auxin is responsible for the phototropism and geotropism.
Auxin helps in promoting root initiation and stem cutting in plants.
Auxin inhibits the growth of lateral bud by stimulating the production of ethylene.
Auxin controls the aging and senescence of plants.
Auxin helps in promoting the growth of many fruits without fertilization.
Auxin helps in delaying the shedding of leaves
2 CYTOKININ are hormones present in the areas of rapid cell division, such as fruits and seeds. They also promote the opening of the stomata.
Cytokinins help in stomatal opening.
Cytokinins help in delaying the senescence of leaves.
Cytokinins promote the expansion of cotyledons.
Cytokinins are involved in the enlargement of stem cells.
Cytokinins are also involved in promoting chloroplast maturation.
3 GIBBERELLINS are hormones that help in the growth of the stem, seed germination, bolting, and flowering.
Gibberellins help in controlling the elongation of the stem in young shoots.
Gibberellins help in seeds germination, enzyme production and food production, which is required for the new cells to grow.
Gibberellins help in promoting flowering, cell division, and growth of seeds after germination.
Gibberellins help in increasing the number of fruits, the size of a fruit and also delay the ripening of fruits in citrus plants.
Gibberellins are also involved in seed germination.
4. ABSCISIC ACID is a hormone that inhibits the growth in various parts. It is also responsible for the closure of stomata.
Abscisic acid helps in promoting bud dormancy and senescence of leaves.
Abscisic acid helps in the closing of stomata during Transpiration.
Abscisic acid inhibits detachment of plant parts.
Abscisic acid plays an important role in seed development, maturation and dormancy.
Abscisic acid helps in slowing the plant growth and protects undeveloped bud during the cold season.
5. ETHYLENE is the hormone which brings in the ripening of fruits.
Ethylene helps in stimulating fruit ripening and determining the sex of a flower.
Ethylene is involved in the production of female flowers in a male plant.
Ethylene promotes Apo-geotropism in roots.
Ethylene helps in the root initiation of plants.
Ethylene increases the speed of senescence.
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.