CHILLING INJURY INDUCES LIPID PHASE-CHANGES IN MEMBRANES OF TOMATO FRUIT

Wide-angle x-ray diffraction has provided evidence for lipid phase sep arations in microsomal membranes from chill-injured tomato (Lycopersic on esculentum Mill. cv Caruso) fruit. Mature-green fruit stored for 20 d at 5 degrees C had not begun to ripen and were essentially free or chilling injury symptoms. Within 4 d of being returned to 25 degrees C , however, the fruit displayed characteristic symptoms of chilling inj ury, including translucent water-soaked patches, surface pitting, and irregular pigmentation. Membrane damage measured as electrolyte leakag e from pericarp discs intensified after the fruit were returned to amb ient temperature. Wide-angle x-ray diffraction patterns recorded at 25 degrees C for microsomal membranes isolated from untreated, mature-gr een fruit indicated that the membrane bilayers were exclusively liquid -crystalline. Diffraction patterns for microsomal membranes from fruit stored for 20 d at 5 degrees C showed only trace amounts of gel phase lipid, but within 4 d of subsequent exposure of the fruit to ambient temperature, there was evidence for a pronounced lateral phase separat ion of lipids within the membranes that would render them leaky. Inasm uch as the phase separations were detectable at 25 degrees C and becam e pronounced only subsequent to the chilling episode, they appear to b e an indirect rather than direct effect of exposure to low temperature . The diffraction data thus support the notion that the lipid phase ch anges observed here are not directly induced by low temperature but ra ther reflect subsequent biochemical changes in the bilayers that may c ontribute to the development of chilling symptoms.