A Comparison of the Properties of ATPase Associated with Wheat and Cauliflower Plasma Membranes

Plasma membrane-associated ATPase obtained from cauliflower (Brassica oleraceae L.) florets isolated and assayed by several different procedures was stimulated 150 to 400% by K(+). In contrast, winter wheat (Triticum aestivum L. cv. Kharkov 22 MC) shoot and root ATPase obtained by the same methods exhibited only 10 to 25% stimulation by K(+). The level of K(+)-stimulation of the wheat enzyme was not significantly increased by purifying the crude microsomal membrane fraction using sucrose density gradients. ATPase associated with density gradient-purified cauliflower membranes was inhibited by Ca(2+), high ATP concentration in the presence of low Mg(2+), and by several metabolic inhibitors. In contrast, the wheat enzyme was largely unaffected by all of these treatments. The plasma membranes of intact wheat and cauliflower cells gave a positive reaction with the plasma membrane-specific, phosphotungstic acid-chromic acid stain (PACP). A high proportion of the cauliflower membrane vesicles in the putative plasma membrane-enriched fraction stained with PACP, whereas only a small proportion of the wheat membrane vesicles reacted positively with PACP. These results indicate that a plasma membrane-enriched fraction has been isolated successfully from cauliflower floret tissue, but that none of the procedures used effectively separate plasma membranes from homogenates of wheat shoots and roots.