ION-TRANSLOCATING ATPASES IN TENDRILS OF BRYONIA-DIOICA JACQ

Procedures have been developed which allow the preparation of highly p ure endoplasmic reticulum and plasma membrane from tendrils of Bryonia dioica. These and further membrane fractions were used to study vanad ate-sensitive ATPase activity as well as Mg2+-ATP-driven transport of Ca-45(2+). Calcium-translocating ATPases were detected in the endoplas mic reticulum, the plasma membrane and the mitochondrial fraction and characterized kinetically and with respect to the effects of various i nhibitors. The endoplasmic-reticulum Ca2+-translocating ATPase was sti mulated by KCl and was calmodulin-dependent. The plasma-membrane enzym e was not affected by these agents. These, as well as the inhibitor da ta, show that the Ca2+-translocating ATPases of the endoplasmic reticu lum and the plasma membrane are distinctly different enzymes. Upon mec hanical stimulation, the activities of the vanadate-sensitive K+, Mg2-ATPase and the Ca2+-translocating ATPase(s) increased rapidly and tra nsiently, indicating that increasing transmembrane proton and calcium fluxes are involved in the early stages of tendril coiling.