1, auxin
Auxin (IAA) can obviously promote the vertical growth of vegetative organs. Low concentration of auxin can promote organ elongation, thus reducing transpiration and water loss. When it exceeds the optimum concentration, it will lead to the production of ethylene, which will reduce the promotion of growth and even turn into inhibition.
Different organs have different responses to auxin. Roots are the most sensitive, buds are the second, and stems are the worst. The main reason why auxin can promote cell elongation is that it can acidify the cell wall environment, increase the activity of hydrolase, relax the cell wall structure, increase the plasticity and increase the cell volume.
The combination of auxin and cytokinin can cause cell division, and auxin alone can also cause cell division. For example, in early spring, the recovery of cambium cell division in trees is caused by the downward transport of auxin produced by terminal buds.
Auxin can also promote the synthesis of RNA and protein, and promote cell division and differentiation. Auxin has duality, which can not only promote plant growth, but also inhibit plant growth. Low concentration auxin promotes plant growth, while high concentration auxin inhibits plant growth. 2,4-D has been used as a selective herbicide.
2. Gibberellin
Gibberellin's most prominent function is to accelerate cell elongation (gibberellin can increase the content of auxin in plants, and auxin can directly regulate cell elongation), it can also promote cell division and cell expansion (but it will not cause cell wall acidification). In addition, gibberellin also has physiological functions of inhibiting maturation, lateral bud dormancy, senescence and tuber formation.
3. Cytokinin
The main function of cytokinin is to promote cell division. Cytokinin can not only promote cell division, but also expand cell volume. However, unlike auxin, cytokinin increases cell volume by expanding and thickening cells laterally, rather than promoting cell longitudinal elongation, which has a certain inhibitory effect on cell elongation.
Cytokinins can also promote bud differentiation. When their content in tissue culture is greater than auxin, callus is easy to germinate; On the contrary, it is easy to take root and sprout. Can be used for preventing abscission, promoting parthenocarpy, thinning flowers and fruits, rooting cuttings and preventing potato germination.
4. abscisic acid
Abscisic acid can inhibit cell division and promote the senescence and abscission of leaves and fruits. Inhibit seed germination. It inhibits the synthesis of RNA and protein, thus inhibiting the growth of stems and lateral buds, so it is a growth inhibitor, which is beneficial to the increase of cell volume. It has antagonistic effect with gibberellin.
Abscisic acid can promote the abscission of petiole by promoting the formation of abscission layer, and can also promote the dormancy of buds and seeds. The higher abscisic acid content in seeds is the main reason for seed dormancy.
5. Ethylene
Ethylene can promote fruit ripening, organ shedding and senescence, induce adventitious roots and root hairs, break the dormancy of plant seeds and buds, inhibit the flowering of many plants (but can induce and promote the flowering of pineapple and related plants), and change the sex and differentiation direction of flowers in the early stage of flower development of dioecious plants.
Its production has a "self-promoting effect", that is, the accumulation of ethylene can stimulate more ethylene production. Ethylene can promote the synthesis of RNA and protein, increase the permeability of cell membrane and accelerate respiration.
Therefore, when the ethylene content in fruit increases, it can promote the transformation of organic matter and accelerate maturity. Ethylene can also promote organ loss and aging. Treating etiolated seedling stems with ethylene can make the stems thicker and the petioles grow upward. Ethylene can also increase the number of female flowers in melon plants, and in plants, it can promote the milk secretion of rubber trees and sumac trees.
Baidu encyclopedia-plant hormones