ATP-Dependent Calcium Transport in Plasmalemma Preparations from Soybean Hypocotyls : EFFECT OF HORMONE TREATMENTS.

A plasmalemma-enriched membrane preparation from etiolated soybean (Glycine max L., cv. Wayne) hypocotyls possesses an active ATP-dependent calcium pump which leads to calcium accumulation when assayed by the methods of Gross and Marmé (1978, Proc Natl Acad Sci USA 75: 1232-1236). Two-hour treatment of segments from the elongating zone of the hypocotyl with growth-promoting concentrations of indoleacetic acid gives up to 100 percent increase in the calcium transport activity. Conversely, similar pretreatment with zeatin or other cytokinins is inhibitory. In the meristematic and maturing zones of the hypocotyl, zeatin has the opposite effect of promoting calcium transport activity. One facet of cell-growth regulation may lie with hormonally mediated changes in efflux pumping of calcium.