PHYTOCHROME-MEDIATED RAPID CHANGES IN THE LEVEL OF PHOSPHOINOSITIDES IN ETIOLATED LEAVES OF Zea mays

The role of the active form of phytochrome in Zea mays on the polyphosphoinositide cycle was studied. As little as 15 s of red irradiation of etiolated leaves immediately increased the level of phosphatidylinositol bisphosphate (PIP₂) 3–6-fold compared to unirradiated leaves. The elevated level of PIP₂ decreased with longer red irradiations up to 5 min, but remained higher than in unirradiated leaves. The level of PIP₂ decreased if red irradiation was followed by far-red irradiation. Far-red alone had no effect. Levels of phosphatidylinositol phosphate (PIP) and phosphatidylinositol did not change significantly. Since red irradiation significantly changed PIP, but not PIP, photocontrol appears to be at the PIP kinase and phospholipase level. In related studies of the effect of light on phospholipids, 5 min of red irradiation induced significant decreases in phosphatidylcholine and phosphatidylethanola-mine.