PLASMA-MEMBRANE PHOSPHOLIPID AND STEROL SYNTHESIS IN SOYBEAN HYPOCOTYL SEGMENTS UNDERGOING AUXIN-INDUCED ELONGATION

Auxin-induced cell elongation necessitates plasma membrane enlargement . The effect of auxin (10 mu M 2,4-dichorophenoxyacetic acid) treatmen t on amount, composition, and rate of synthesis of plasma membrane lip ids was examined. Auxin-treated and control soybean (Glycine max L.) h ypocotyl segments were incubated with [C-14]acetate for times ranging from 0.5 to 18 h, prior to isolation of plasma membrane by aqueous two -phase partitioning. The composition of individual plasma membrane lip ids in elongating segments did not differ from the composition in trea tment time-matched control segments, except that after longer auxin tr eatments, phospholipids had more unsaturated fatty acids. Plasma membr ane phospholipid and free sterol content both increased in elongating segments. The relative proportion of sterols and phospholipids in the plasma membrane primarily depended on time after segment excision, for both auxin-treated and control segments. Auxin enhanced the rate of l ipid incorporation into the plasma membrane by 6 h, and stimulated the synthesis of some phospholipids and sterols.