The growth and development of plants are influenced by external environmental conditions such as water, sunlight, soil and temperature, and controlled by internal genetic factors, while some metabolic substances, namely plant hormones, regulate the physiological activities of plants. The discovery of plant hormones is a great progress in the field of biology. It promotes the application of "chemical regulation" in agriculture and makes it possible for people to change the inherent mode of plant growth and development through chemical regulation. The purpose of studying plant hormones is not only to reveal the mechanism and regulation law in the process of plant growth and development regulation, but also to explore the application technology of plant growth substances, so that they can adjust plant growth and development according to production needs and improve crop quality and yield.

Since the discovery of the first plant hormone auxin, people have synthesized many compounds with physiological activities in the study of simulating natural hormones, that is, plant growth regulators. At present, there are thousands of plant growth substances (plant hormones and plant growth regulators), but only dozens of them are widely used in agriculture and gardening. People can promote or inhibit the growth of crops and horticultural crops through chemical regulation and control, increase the yield, and provide favorable conditions for mechanized management and harvest. The application of plant growth substances also provides some convenient conditions for people in plant cultivation and breeding. In other words, plant growth substances are used to regulate the synthesis and metabolism of plant hormones in plants, the direction of transportation and the balance between various hormones. At present, chemical control technology has been widely used in agriculture, forestry, animal husbandry, horticulture, flowers, breeding, cultivation management, improving plant stress resistance and other fields, and has achieved certain results, which has attracted the attention of biological and chemical scientists and cultivation and breeding workers. In some cases, the production effect of rational application of plant growth substances is even much faster than that of cultivation and breeding.

……