Plant Growth Regulators (PGR)
Plant growth regulators may be defined as any organic compounds, which are active at low concentrations(1-10ng/nl) in promoting, inhibiting or modifying growth and development. The naturally occurring (endogenous) growth substances are commonly known as plant hormones, while the synthetic ones are called growth regulators.
Plant hormones is an organic compound synthesised in one part of the plant and translocated to another part, where very low concentrations it causes a physiological response. The plant hormones are identified as promoters(auxins,gibberellin,cytokinin),inhibitors(abscissic acid and ethylene) and other hypothetical growth substance (florigen, flowering hormones, etc..)