Signal transduction in plants: evidence for the involvement of calcium and turnover of inositol phospholipids.

Involvement of calcium and turnover of inositol phospholipids in signal transduction was investigated using roots of a variety of corn (Zea mays L., cv. Merit) which require light to develop gravitropic sensitivity. Depletion of calcium in root tips by EGTA plus calcium ionophore A23187 prior to light treatment resulted in the loss of light-dependent gravisensitivity. Replenishment of calcium to depleted roots restored the light-dependent gravisensitivity. Light treatment of dark-grown roots resulted in an increased level of inositol trisphosphate as compared to controls. Furthermore, 5-hydroxytryptamine, which is known to promote the hydrolysis of phosphoinositides, sensitized dark-grown roots to gravity and increased inositol trisphosphate levels. These results support the hypothesis that calcium and inositol phospholipid turnover play a role in signal transduction in plants.