Gibberellic acid-stimulated alpha-amylase secretion and phospholipid metabolism in wheat aleurone tissue.

1. Turnovers of [14C]glycerol-labelled phospholipids in wheat aleurone tissue have been measured by using a pulse-decay technique. The most metabolically active phospholipids were phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine and phosphatidylglycerol. 2. Gibberellic acid action on the tissue led to breakdown of phosphatidylcholine and stimulated turnover of the other phosphatides concomitant with the secretion of alpha-amylase from the tissue. After pulse-labelling of the aleurone tissue with [14C]glycerol, radioactivity was lost from the phospholipids and appeared quantitatively in triacylglycerols, suggesting a stoichiometric metabolism of the former into the latter. Although 1,2-diacylglycerol is an expected intermediate in such a conversion, the patterns of radioactivity in diacylglycerols gave no indication of this. 3. Several aspects of the response of aleurone tissue to gibberellic acid resemble the responses of exocytotic animal tissues to external agonists. In particular, our results and previous reports in the literature suggest that endomembrane flow, exocytosis, phosphatidylinositol turnover and a requirement of Ca2+ for enzyme secretion are common to both plant and animal systems. Although considerable differences also exist between the two, the similarities are sufficient to warrant further consideration that plants and animals might have conserved a similar hormone response-secretion mechanism.