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The proton pumping ATPase in the plasma membrane of Elodea canadensis is believed to playa major role in inorganic carbon acquisition. To investigate potentially different carbon uptake strategies within the same plant. plasma membrane H+-ATPase distribution and polar current patterns 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 W -ATPase, yielded strongly visible double bands at 100 kDa in leaf microsome preparations. whereas little antigen was detected in analogous stem microsome preparations.Several accumulated arguments reveal the PM-H+-ATPase as the ATP-dependent H+-extruding system in Elodea densa leaves (Marre et al., 1988(Marre et al., , 1989 Trockner and Marre, 1988). This enzyme would thus be responsible for acidification at the

Microwave-enhanced fixation of animal tissues for electron microscopy has gained in interest in recent years. Attempts to use microwave irradiation for the preparation of plant tissues are rare. In this study; I report on microwave conditions which allow a high quality preservation of plant cell structure. Tissues used were: internodes of Chara vulgaris, leaves of Hordeum vulgare, root tips of Lepidium sativum. Microwave irradiation was done with a commercial microwave oven (Sharp R-5975). Fixatives used were: 2.5% glutaraldehyde in 0.1 M sodium cacodylate buffer, pH 7.2 and 1% osmium tetroxide in veronal/acetate buffer, pH 7.2. Conventional fixations with glutaraldehyde/osmium were compared with microwave fixations. Examinations of thin sections showed that microwave fixation (glutaraldehyde or sequential aldehyde/osmium) is an attractive and rapid alternative method for processing plant tissues for electron microscopy. The optimal conditions found were: microwave oven at power level 50 W, 6.5 ml of fixative solution, irradiation times between 32-34 s, final temperature between 40 degrees C and 47 degrees C.

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Electron dense deposits (EDD) were observed on the extracellular side of the plasmalemma of Chara internodal cells by a calcium-glutaraldehyde fixation technique. The number and size of EDD were greatly increased when cells had been preincubated in Ca2+-enriched medium before fixation. The addition of Na+, Mg2+, or La3+ instead of Ca2+ in incubation and fixation media produced no deposits at all, Sr2+ caused deposits with similar distribution to those formed by Ca2+, and Ba2+ addition resulted in deposits localized at different sites within the cell. Microprobe analysis of single EDD from Ca2+ incubated cells ascertained the presence of calcium in these deposits. Possible functions of the Ca2+-binding sites at the plasma membrane of Chara cells are discussed.