Phytohormones are a kind of organic compounds with physiological activity produced in plants. They can be transferred from synthetic sites to functional sites, which can promote, inhibit or change some physiological processes of plants. Up to now, there are six kinds of plant growth regulators used: auxin, gibberellin, cytokinin, ethylene, growth retardants (inhibitors) and other plant growth regulators.
The chemical name of 1. auxin is 3- indoleacetic acid (IAA). The most obvious effect of IAA on forest growth is to promote cell elongation (increase cell plasticity, increase enzyme synthesis, promote bond breakage and new cell wall synthesis, enhance plasma membrane transparency and enhance water absorption). The effect of IAA on growth increases with the increase of concentration, but it will cause obvious inhibition when it reaches a certain concentration. IAA can also promote cambium activity, adventitious root formation, prevent senescence, promote or delay abscission, form apical dominance, promote fruit setting and parthenocarpy. Such as 3- indoleacetic acid (IAA), indolebutyric acid (IBA), naphthylacetic acid (NAA), naphthoxyacetic acid (NOA), dichlorophenoxyacetic acid (2,4,5-trichlorophenoxyacetic acid (2,4,5-t) and 2- methyl -4- monochlorophenoxyacetic acid.
2. There are 72 kinds of gibberellin (GA) in plants, namely GA 1 ~ 72. Its main function is to stimulate cell elongation and obviously promote internode elongation, but it does not affect the number of internodes. The effect of GA on plant growth increased with the increase of concentration, but it did not increase after reaching a certain concentration, and there was no inhibition. Gibberellin can promote fruit setting, increase fruit, induce parthenocarpy and prevent aging. GA did not affect photosynthetic intensity, but significantly increased respiratory intensity. In fruit tree cultivation, the functions of GA mainly include inhibiting flower bud formation, breaking dormancy, promoting seedling growth, promoting seedless (grape) fruit size and improving fruit shape.
3. Cytokinin (CTK), also known as cytokinin, is a derivative of purine. Its main physiological function is to promote cell division and expansion, promote bud germination, overcome apical dominance, promote lateral bud germination, delay the degradation of protein and chlorophyll, thus delaying senescence and promoting the formation of fruit setting and flower buds. Such as 6- phenylaminopurine (6-BA, BAP), PBA, DPU, benzoate, etc., have the functions of promoting fruit setting, improving fruit shape index, promoting lateral bud germination and promoting cell division.
4. The most obvious biological effects of ethylene are triple response (inhibiting the elongation growth of stems and promoting the expansion growth) and upward reaction (the upper part of petiole grows fast and the lower part grows slowly, making the leaves droop and curl). Ethylene can promote fruit ripening, flower bud formation, defoliation, flower drop and fruit drop, and inhibit vegetative growth. Such as ethephon (Ethephon, trhephon, CEPA), ethylene silicon (CGA- 1528 1, Silaid), AVG, its main functions are inhibiting vegetative growth, promoting flower bud formation, assisting mechanical harvesting, promoting mature coloring, thinning flowers and fruits, delaying flowering and early dormancy.
5. Growth retardants and growth inhibitors. Growth retardants mainly inhibit the division and elongation of meristem cells in shoot tips, which can be reversed by gibberellin. However, growth inhibition completely inhibited the growth of meristem at the tip of new shoots, which could not be reversed by gibberellin. Such as chlormequat (ccc, cycocel, chloyeguat), Morphactin(chluflurecol, Maintain), cyanic acid (MH, Malehydrazide), triiodobenzoic acid (TIBA), phosphine amine, paclobutrazol (pp333, Cultar), its main functions are inhibiting vegetative growth, promoting flowering and increasing fruit setting.
6. Other plant growth regulators, such as triacontanol (TRIA, TAL,1-triacontanol), brassinolide, etc., have the effects of GA and CTK, but their activities are lost after alkali treatment and can be recovered after acid treatment. In addition, plant growth regulator compounds, such as Promailin and Ba, are also used.