Plant growth regulators (also known as growth regulators or plant hormones) are signal molecules naturally produced by plants that control normal plant functions, such as root growth, fruit set and drop, growth and other development processes and occur in extremely low concentrations.
Plant growth regulators are vital to plant growth and lacking them, plants would be mostly a mass of undifferentiated cells. They regulate cellular processes in targeted cells locally and when moved to other locations, in other locations of the plant. Hormones also determine the formation of flowers, stems, leaves, the shedding of leaves, and the development and ripening of fruit. Plant hormones shape the plant, affecting seed growth, time of flowering, the sex of flowers, senescence of leaves and fruits.
Based on structural similarities and on effects on plant physiology, it is accepted that there are five major classes of plant hormones including Abscisic acid (ABA), Auxins, Cytokinins (CK), Ethylene and Gibberellins (GAs). Each class has positive as well as inhibitory functions, and most often work in tandem with each other, with varying ratios of one or more interplaying to affect growth regulation.
Classification in " Plant growth regulators "