Electron paramagnetic resonance-spectroscopic studies on spin-labeled purified tonoplast membranes showed that in the obligate crassulacean-acid-metabolism (CAM) plant Kalanchoë daigremontiana Hamet et Perr. the fluidity of the tonoplast decreased during acclimation to higher temperatures. This phenotypic change in tonoplast fluidity was paralleled by a decrease in the mobilization of malic acid from the vacuoles during CAM in the light. The shift from the C3 to the CAM mode of photosynthesis in the facultative CAM plant Mesembryanthemum crystallinum L. also led to a decrease in the fluidity of the tonoplast membrane. The results are consistent with the hypothesis that the ability to store malic acid during CAM in the vacuoles depends largely on the actual fluidity of the tonoplast membrane.

No abstract

Comparative electron paramagnetic resonance spectroscopic studies on spin-labeled native and protein-free purified tonoplast membranes in the CAM plant Kalanchoe daigremontiana showed that the phenotypic decrease in tonoplast fluidity occurring upon acclimation to elevated temperature is brought about by specific protein-lipid interaction. However, there are indications that, to some extent, the properties of the bulk tonoplast lipids may also be affected by acclimation to high temperature. In contrast to heat acclimated individuals and for still unknown reasons, in plants grown at normal temperature depletion of the tonoplast membrane of its proteins had no effect on membrane fluidity. The results are considered as evidence for the occurrence of homeoviscous adaptation in the tonoplast of CAM plants towards changes in the temperature climate during growth.