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

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Abstract
Plasma membrane-associated ATPase obtained from cauliflower (B. oleracea L.) florets isolated and assayed by several different procedures was stimulated 150-400% by K+. Winter wheat (T. aestivum L. cv. Kharkov 22 MC) shoot and root ATPase obtained by the same methods exhibited only 10-25% 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 Ca2+, high ATP concentration in the presence of low Mg2+ and by several metabolic inhibitors. 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. Apparently, a plasma membrane-enriched fraction was isolated successfully from cauliflower floret tissue, but none of the procedures used effectively separate plasma membranes from homogenates of wheat shoots and roots.