Plant growth regulators are usually divided into five types: auxin, gibberellin, cytokinin, abscisic acid and ethylene. In addition to the above five kinds, some new natural hormones have been found, such as brassinolide isolated from rape pollen. Some synthetic organic compounds also have the properties of natural hormones, and their efficacy even exceeds that of natural hormones. Such as naphthylacetic acid, chlormequat chloride, 2,4-Didi, malazide, fruit bulking agent (Li Guolin), etc. Its functions are as follows:
(1) auxin
Auxin in plants is mainly produced in new shoots, young leaves and developing embryos, which has the characteristics of polar transportation. Auxin can control the expansion rate of cells by affecting the flexibility of cell walls, promote the elongation of cells, stimulate the cell division of cambium in new shoots and stems when transported downward from new shoots, inhibit the development of lateral buds and prevent aging. Auxin is mainly used to promote cutting rooting, flower thinning and fruit thinning of fruit trees, and also widely used to prevent fruit from falling before harvest and control germination.
(2) Gibberellin
Gibberellin in plants is mainly produced in young leaves, young embryos and roots, and has no obvious polar transport characteristics. Gibberellin is used externally on fruit trees, and its fluidity is also poor, and its efficacy has obvious limitations. The main functions of gibberellin are: to promote the elongation of internodes of new shoots of fruit trees, thus promoting the growth of new shoots; Break the dormancy of buds and seeds and promote the germination of seeds and buds; Inhibit the formation of flower buds and reduce the amount of flowers; Used together with auxin to prevent young fruit from falling off and promote fruit expansion. In addition, gibberellin can also delay fruit ripening.
(3) Cytokinin
Cytokinins in plants are synthesized in roots and young fruits. Cytokinins synthesized in roots are transported upward through xylem, while cytokinins synthesized in fruits or used outside trees are transported downward through phloem. Cytokinin has the function of regulating the transport of nutrients, thus promoting cell division, relieving apical dominance, promoting branching, increasing the number of flower buds and preventing flowers, fruits and leaves from aging and falling off.
(4) Ethylene
Ethylene promotes fruit ripening and is called "ripening hormone". It can delay the growth and make the stem shorter and thicker; Inducing organ shedding and seedling defoliation; It is also used for thinning flowers and fruits of fruit trees in production. In addition, ethylene can also break dormancy, promote germination, form root hairs, promote flowering, yellow leaves and flower organ withering, and can also inhibit the development of lateral buds when used in combination with auxin. Ethephon is commonly used in production.
(5) abscisic acid
As an endogenous hormone, abscisic acid has antagonistic effect on gibberellin, auxin, cytokinin and other hormones that promote cell division and growth, and is the most important growth inhibitor. But it is rarely used in fruit trees at present. Synthetic growth retardants or growth inhibitors, such as triiodobenzoic acid, chlormequat chloride and 2,4-D, are often used in fruit trees. It can dwarf trees, shorten internodes, increase branches, promote flower bud formation, improve fruit setting rate and promote dormancy.
(6) fruit expanding agent
Fruit bulking agent is a synthetic plant growth regulator, which mainly promotes cell division of fruit and increases cell gap, thus making fruit bigger.