Plant growth regulators are organic compounds that can be synthetic or naturally derived from microorganisms. They have similar effects on growth and development as natural plant hormones, and they are essential inputs for modern agricultural growth.

Some common plant growth regulators include fast-acting aminoglutethimide (DA-6), chlorpyrifos, sodium nitinol, brassin, and gibberellin. However, there are many more types of plant growth regulators, each with its unique roles and functions.

One example of a plant growth regulator is gibberellins (GAs), which currently have over 100 kinds of isomers expressed by GAs. Common ones include GA3 (nine twenty 0) and GA4+7. Gibberellins can break seed dormancy, promote seedling growth (dormant seedlings), inhibit flower bud formation, improve fruit set rate, induce unisexual fruit set, promote the enlargement of seedless grapes, and change fruit shape. Japanese scientists Sadaharu Yabuta and Sumiki Sakusuke isolated the active substance in 1938 from the filtrate of Erysipelas culture medium and named it erythromycin.

By 1983, more than 60 substances similar to erythromycin had been identified. Generally, gibberellins are divided into two categories: free state and bound state, collectively known as erythromycin. They are named GA1 and GA2, respectively. The biological activity of different erythromycin types varies, with erythromycin (GA3) having the highest activity. The most prominent role of gibberellins is to accelerate cell elongation by increasing the content of growth hormone in plants, which directly regulates cell elongation. Gibberellins can also promote cell division and expansion but do not cause acidification of the cell wall.

Another type of plant growth regulator is cytokinin (CTK), which is a class of plant hormones that promote cell division, induce the formation of shoots, and promote their growth.

Commonly used cytokinins include ZT, BA, CPPU, and TDZ. In 1955, American scientist Skoog and others discovered a substance that promotes cell division when studying plant tissue culture and named it an agonist. Its chemical name is 6-furfurylaminopurine, and it does not exist in the plant body. Later, more than a dozen substances with the physiological activity of agonists were isolated in plants.

All substances with the same physiological activity as agonists, whether natural or synthetic, are now collectively referred to as cytokinins. The main functions of cytokinins are to promote fruit set, prevent fruit drop, regulate fruit shape, promote the sprouting of lateral buds, promote fruit enlargement, and thin fruit, delay leaf senescence, and induce the differentiation of buds.

Abscisic acid (ABA) is another natural growth regulator of plants. Natural active abscisic acid (+)-ABA is very expensive, and the traditional chemical synthesis method of producing abscisic acid is also costly. Due to the high cost and differences in activity, abscisic acid is not widely used in agricultural production.

Only developed countries such as Japan and the United States use it in large-scale agricultural production. Scientists in various countries are looking for ways to produce natural abscisic acid cheaply. The physiological role of abscisic acid is mainly to cause dormancy and promote abscission.

The role of abscisic acid is also opposite to that of cytokinin, as it has antagonistic effects on gibberellins and cytokinins in plants.