Identification of Ca2+‐stimulated polyphosphoinositide phospholipase C in isolated plant plasma membranes

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Abstract
A polyphosphoinositide phospholipase C has been identified in highly purified plasma membranes from shoots and roots of wheat seedlings. The enzyme preferentially hydrolysed phosphatidylinositol 4‐phosphate and phosphatidylinositol 4,5‐bisphosphate and had a different phosphoinositide substrate profile from soluble phospholipase C. The enzyme activity was lower in plasma membranes isolated from light‐grown shoots than from dark‐grown ones, whereas no differences in activity between plasma membranes from light‐ and dark‐grown roots were seen. Maximum activity of the membrane‐bound enzyme was observed around pH 6. It was activated by micromolar concentrations of Ca2+, but not by GTP or GTP analogues. The enzyme may participate in signal transduction over the plant plasma membrane.