DISTRIBUTION OF PLASMA-MEMBRANE H-ATPASE AND POLAR CURRENT PATTERNS IN LEAVES AND STEMS OF ELODEA-CANADENSIS()

The proton pumping ATPase in the plasma membrane of Elodea canadensis is believed to play a major role in inorganic carbon acquisition. To i nvestigate potentially different carbon uptake strategies within the s ame plant, plasma membrane H+-ATPase distribution and polar current pa tterns were investigated in Elodea leaves and stems. Specific activity of plasma membrane H+-ATPase in leaf microsomal fractions was tenfold higher than in stem derived microsomes. Probing western blots with a monoclonal antibody specific for plasma membrane H+-ATPase, yielded st rongly visible double bands at 100 kDa in leaf microsome preparations, whereas little antigen was detected in analogous stem microsome prepa rations. Using the same plasma membrane H+-ATPase specific antibody on tissue sections, the enzyme was found almost exclusively localized at the border of cells at the lower leaf surface. A positive ion current leaving the lower leaf surface was measured, using a vibrating probe device. Part of this current entered the upper leaf surface and part o f it the internodes of the stem. The experimental results support the view, that Elodea leaves have different means of inorganic carbon upta ke than stem internodes.