Plant Growth Hormones: Internal Control Points

Publisher Website
Google Scholar
Abstract
Examples of control points involved in regulation of the availability or action of certain plant hormones are presented. The effects of divalent ions, environmental factors, and other hormones on hormone synthesis, release, or action are illustrated. The role of GA in promoting cell enlargement and division in intact plants is analyzed in view of the paradoxical inhibition of cell division in tissue and suspension culture by GA3. The importance of the intact subapical region as a target site is underlined, but the possibility is raised that GA only play an indirect role in regulation of cell multiplication at this site. The cereal aleurone layer as a target site for GA action is discussed with the objective of identifying the primary control points. Analysis of existing information most favors a role for GA in stimulating synthesis of mRNA, and intervening in transcription or translation. There is a paucity of evidence for specific binding sites for plant hormones. With the exception of hydrolases induced by GA in cereal aleurones, a major limitation to research progress on hormone binding is the lack of evidence for specific functional protein products of hormone action. Membranes undoubtedly play a role in plant hormone action, but evidence for specific regulation of membrane synthesis or of membrane participation in plant responses to hormonal treatment is scarce. The field of plant hormones remains open to serious investigation and basic studies in synthesis, compartmentation and action deserve much more attention.