These promote cell division, differentiation, and elongation in plants. They enhance the growth of vegetative organs and reproductive organs, prevent fruit drop, encourage rooting and germination, and induce parthenocarpy. Their regulatory effects are similar to those of endogenous plant hormones such as auxins, cytokinins, or gibberellins. Common plant growth promoters include indole-3-acetic acid, indole-3-butyric acid, -naphthaleneacetic acid, 6-benzylaminopurine, 4-chlorophenoxyacetic acid, and 2,4-dichlorophenoxyacetic acid.

These inhibit the growth of sub-apical meristems, reducing internode elongation without suppressing apical bud growth. This results in shorter, thicker stems, increased leaf thickness, and higher chlorophyll content. Their action is primarily through regulating gibberellin synthesis, and their effects can be reversed by applying gibberellins. Common plant growth retardants include chlormequat, mepiquat chloride, paclobutrazol, daminozide, uniconazole, and trinexapac-ethyl.

Wide Range of Action and Applications: PGRs are suitable for almost all higher and lower plants in agriculture. By regulating physiological processes such as photosynthesis, respiration, nutrient absorption and transport, signal transduction, stomatal behavior, osmotic pressure, and transpiration, they control plant growth and development, improve plant-environment interactions, enhance crop resilience, increase yields, and improve product quality.