Phosphatidylinositol turnover in isolated soybean membranes stimulated by the synthetic growth hormone 2,4-dichlorophenoxyacetic acid.

Phospholipids of plant membranes isolated from homogenates of dark-grown hypocotyls of soybean (Glycine max L.) undergo rapid and specific degradative changes. The degradation of phosphatidylinositol (PI) in such membranes is enhanced in the presence of the synthetic auxin, 2,4-dichlorophenoxyacetic acid (2,4-D), measured as the hydrolysis of PI or by an enhancement of [3H]inositol incorporation into membrane-associated PI stimulated by Mn2+, but not dependent upon added CTP, Mg2+, or diglyceride. The response is rapid and enhanced by auxin throughout the physiological range of growth-promoting concentrations (optimum at about 7 X 10(-7) M). The growth-inactive 2,4-D analogue, 2,3-dichlorophenoxyacetic acid (2,3-D), is without effect. These findings suggest a cell-free response of isolated membranes to the hormone mediated by a definable enzymatic reaction.