PHENOTYPIC ADAPTATION OF TONOPLAST FLUIDITY TO GROWTH TEMPERATURE IN THE CAM PLANT KALANCHOE-DAIGREMONTIANA HAM. ET PER. IS ACCOMPANIED BY CHANGES IN THE MEMBRANE PHOSPHOLIPID AND PROTEIN-COMPOSITION

The present study deals with the phenotypic adaptation of tonoplast fl uidity in the CAM plant Kalanchoe daigremontiana to changes in growth temperature. Tonoplast fluidity was characterized by measuring fluores cence depolarization in membranes labeled with fluorescent fatty acid analogues and by following formation of eximeres in membranes labeled by eximere-forming fluorophores. With both techniques it was found tha t exposure of the plants to higher growth temperature compared with th e control decreased the fluidity of the tonoplast while exposure to lo wer growth temperature caused the opposite. Three hours of high temper ature treatment (raised from 25 degrees C to 35 degrees C; ''heat shoc k'') were sufficient to decrease the tonoplast fluidity to roughly the same extent as growth under high temperature for 30 days. The phenoty pic response of tonoplast fluidity to changes in growth temperature wa s found only in the complete membrane, not however in the lipid matrix deprived of the membrane proteins. Heat treatments of the plants decr eased the lipid/protein ratio while exposure to low temperature (for 3 0 days) increased it. Heat treatments led to a decrease in the percent age of linolenic acid (C18:3) and linoleic acid (C18:2), heat shock an d low temperature treatments induced an increase in the percentage of linoleic acid (C18:3), with concomitant decrease in the percentage of linoleic acid (C18:2). However, in the case of heat shock, increase in linolenic acid concerned mainly monogalactosyldiacylglycerol, while w ith low temperature treatment linoleic acid increased in phosphatidylc holine. Both treatment of the plants with high and low temperature led to a slight decrease in the contribution of phosphatidylcholine and p hosphoethanolamine to the total phospholipid content of the tonoplast. High-temperature treatment of the plants not only decreased the phosp holipid/protein ratio in the tonoplast, but also led to the occurrence of a 35 kDa polypeptide in the tonoplast which cross-reacted with an antiserum against the tonoplast H+-ATPase holoenzyme. The important ro le of membrane proteins in bringing about the phenotypic rigidization of the tonoplast was mimicked by reconstitution experiments showing th at incorporation of the proteins isolated from the tonoplast into phos phatidylcholine vesicles decreased the fluidity of this membrane syste m. As to be expected from the analyses in the natural membrane, the de gree of this effect depended on the phospholipid/protein ratio.