According to the University of Florida Institute of Food and Agricultural Sciences, plant growth regulators alter hormone responses to control plant functions, including the plant's growth and development. The regulators work on plant hormones, many of which serve multiple functions. For this reason, a single plant regulator used by agriculturalists or horticulturalists can either provide several benefits or have a single benefit with unintended drawbacks.
Growth regulators were first used to regulate flower production in pineapples in the first half of the 20th century. As new hormones were uncovered, such as those regulating leaf production and plant height, substances that affected these hormones were developed, tested and eventually released for both crop and ornamental plant production and sale.
There are six major classes of plant growth regulator. Ethylene enhancers, the regulator first used on pineapples, controls fruit ripening. Growth inhibitors and retardants act much as their name implies; the inhibitors stop growth, while the retardants only slow it down. Auxins serve multiple purposes, helping with flower production and enhancing root growth while simultaneously elongating plant shoots. Cytokinins stimulate cell division in buds, roots, blooms and protective cells to prolong the plant's shelf life. To elongate cells and make flowers and fruits larger, growers apply gibberellins.
Growth regulators can either enhance or retard the activity of a plant hormone. For example, if a more compact and uniform plant is desired, plant nurseries might treat the plant with a growth retardant. To keep plants from drying out or using up all their soil nutrients during shipping, growers may treat plants with growth inhibitors before shipping them long distances.
Crops Commonly Used On
Vegetables are treated with ethylene generators so they all ripen at the same time and can be harvested in one go. Then they're treated with cytokinins to prolong their shelf life. Long-stem cut flowers such as roses are treated with gibberellins to ensure long, strong stalks and large, attractive blooms. Auxins are especially useful on plants whose flowers are desirable but whose fruit is not, such as ornamental roses. The auxins cause fruit drop but increase flower production.