Response of Isolated Plant Membranes to Auxins: Calcium Release

Abstract

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