Response of Isolated Plant Membranes to Auxins: Calcium Release

Abstract

Membranes from etiolated hypocotyls of soybean (Glycine max [L.] Merr.) cultivar Wayne were loaded with 45Ca in the presence of the ionophore A23187. Upon subsequent treatment with 2,4-D or IAA, Ca was released. A weak or inactive auxin analog (2,3-D, 2,3-dichlorophenoxyacetic acid) did not promote release from the hypocotyl membranes, nor did red blood cells treated with either auxin release Ca. The concentration dependency of auxin-promoted Ca release paralleled that of auxin-induced growth and was biphasic with an optimum at 1 .mu.M. Membrane vesicles from mung bean Vigna radiata cv. Jumbo hypocotyls and pea [Pisum sativum cv. Alaska] epicotyls released Ca in response to auxin. The similar concentration dependency of auxin-induced growth and of Ca release and the fact that most of the in vitro responses of plant plasma membranes to auxin are duplicated by appropriate modulation of membrane Ca suggest a role of Ca ions in the responses of plant membranes to auxins.