EFFECTS OF GIBBERELLIC-ACID AND ENVIRONMENTAL-FACTORS ON CYTOSOLIC CALCIUM IN WHEAT ALEURONE CELLS

Gibberellins (GAs) control a wide range of physiological functions in plants from germination to flowering. The cellular mechanisms by which gibberellic acid (GA(3)) acts have been most extensively studied in t he cereal aleurone. In this tissue, alterations in cellular calcium ar e known to be important for the primary response to GA, which is the p roduction and secretion of hydrolytic enzymes. The extent to which cyt osolic Ca2+ mediates the early events in GA action, however, is not kn own. In order to address this question, changes in cytosolic Ca2+ in w heat (Triticum aestivum L. cv. Inia) aleurone cells that occur rapidly after treatment with GA were characterized. In addition, GA-induced c hanges were compared with changes induced by,three environmental stimu li that are known to modify the GA response: osmotic stress, salt (NaC l), and hypoxia. The Ca2+-sensitive dye fluo-3 was used to photometric ally measure cytosolic Ca2+. It was found that GA, induced a steady-st ate increase in cytosolic Ca2+ of 100-500 nM. This increase was initia ted within a few minutes of treatment with GA and was fully developed after 30-90 min. The changes in cytosolic Ca2+ that were induced by GA were distinct from those induced by mannitol, NaCl, or hypoxia. Manni tol caused a steady-state decrease whereas NaCl and hypoxia both incre ased cytosolic Ca2+. In the case of NaCl this increase was transient b ut for hypoxia the increase was prolonged as long as hypoxic condition s were maintained. Gibberellin-induced changes in cytosolic Ca2+ were not induced by the inactive GA, GAs, nor did the GA-insensitive wheat mutant, D6899, respond to active GA, with altered cytosolic Ca2+. It i s concluded that changes in cytosolic Ca2+ are an early and integral p art of the GA response in aleurone cells. The data also indicate, howe ver, that changes in Ca2+ are not sufficient, by themselves, to induce the GA response of aleurone cells.