Isolation of presumptive plasma membranes from a characean alga

Abstract

The internodal cells of characean algae were frequently used as experimental models in studies of plant cell membrane control. However, these studies lacked a well defined in vitro system. Therefore, a method was introduced, based on membrane partitioning on an aqueous two-phase polymer system, by which the plasma membrane fraction from a characean alga (Chara gymnophylla) was isolated for the first time. The plasma membranes were identified on electron-micrographs by phosphotungstic acid-chromic acid (PTAC) selective staining. The specific adenosine triphosphatase (ATPase) activity in the plasma membrane fraction was 20 ± 4 nmol Pi/min per mg, and it was sensitive to the inhibitor of the plasma membrane ATPase, vanadate. Inhibitors of ATPase of other origin had a smaller influence (azide, nitrate), or showed no inhibition (oligomycin). While dependent on Mg2+, the plasma membrane ATPase showed a very low sensitivity to K+, suggesting that it is not a H+, K+ exchanging ATPase as inferred from studies on intact cells. © 1992.