Phenotypic Adaptation to Elevated Temperatures of Tonoplast Fluidity in the CAM Plant Kalanchoë daigremontiana is Caused by Membrane Proteins*

Comparative electron paramagnetic resonance spectroscopic studies on spin-labeled native and protein-free purified tonoplast membranes in the CAM plant Kalanchoë 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.