Plant hormones are a kind of organic substances produced by plants' own metabolism, which have obvious physiological effects at very low concentrations when they move from the production site to the action site. They are also called plant natural hormones or plant endogenous hormones. They regulate the growth, development and differentiation of plants in cell division and elongation, tissue and organ differentiation, flowering and fruiting, maturity and senescence, dormancy and germination, and in vitro tissue culture. The flexibility and diversity of this regulation can be achieved by changing the concentration and proportion of exogenous hormones or synthetic plant growth regulators, and then changing the level and balance of endogenous hormones.

There are six kinds of plant hormones: auxin (Auxin), gibberellin (GA), cytokinin (CTK), abscisic acid (ABA), ethylene (acetylene) and brassinolide (BR). They are all simple small molecular organic compounds, but their physiological functions are very complicated and diverse. For example, from affecting cell division, elongation and differentiation to affecting plant germination, rooting, flowering, fruiting, sex determination, dormancy and shedding. Therefore, plant hormones play an important role in regulating the growth and development of plants.