Plasma membrane isolation from freshwater and salt-tolerant species of Chara: Antibody cross-reactions and phosphohydrolase activities

Plasma membranes were isolated using the aqueous polymer two-phase partition method from the algae Chara corallina and Chara longifolia, algae which differ in their ability to grow in saline environments, Enrichment of plasma membrane and depletion of tonoplast relative to the microsomal fraction was monitored using phosphohydrolase assays and cross-reactions to antibodies raised against higher plant transporters. Antibodies to the vacuolar ATPase and pyrophosphatase cross-reacted with epitopes in the microsomal fraction, but showed little affinity for the plasma membrane fraction. Pyrophosphatase activity also declined in the plasma membrane fraction relative to the microsomal fraction. The V-type H⁺-ATPase activity, sensitive to nitrate or bafilomycin, was low in both fractions, though the cross-reaction to the antibody was reduced in the plasma membrane fraction. By contrast, the antibody recognition of a P-type H⁺ ATPase amino acid sequence from Arabidopsis did not occur strongly in the anticipated 90-100kDa range. While there was enhanced recognition of a polypeptide at around 140 kDa in the plasma membrane fraction, salt treatment of Chara longifolia resulted in plasma membrane fractions with reduced amounts of this epitope, but no change in vanadate-sensitive ATPase activity, suggesting that it does not represent the only P-type ATPase. Microsomal membranes from salt-adapted C. longifolia have higher reactivity with the antibody to the tonoplast ATPase.