UNSATURATION OF THE MEMBRANE-LIPIDS OF CHLOROPLASTS STABILIZES THE PHOTOSYNTHETIC MACHINERY AGAINST LOW-TEMPERATURE PHOTOINHIBITION IN TRANSGENIC TOBACCO PLANTS

Using tobacco plants that had been transformed with the cDNA for glyce rol-3-phosphate acyltransferase, we have demonstrated that chilling to lerance is affected by the levels of unsaturated membrane lipids, In t he present study, we examined the effects of the transformation of tob acco plants with cDNA for glycerol-3-phosphate acyltransferase from sq uash on the unsaturation of fatty acids in thylakoid membrane lipids a nd the response of photosynthesis to various temperatures. Of the four major lipid classes is elated from the thylakoid membranes, phosphati dylglycerol showed the most conspicuous decrease in the level of unsat uration in the transformed plants. The isolated thylakoid membranes fr om wild-type and transgenic plants did not significantly differ from e ach other in terms of the sensitivity of photosystem II to high and lo w temperatures and also to photoinhibition. However, leaves of the tra nsformed plants were more sensitive to photoinhibition than those of w ild-type plants. Moreover, the recovery of photosynthesis from photoin hibition in leaves of wild-type plants was faster than that in leaves of the transgenic tobacco plants. These results suggest that unsaturat ion of fatty acids of phosphatidylglycerol in thylakoid membranes stab ilizes the photosynthetic machinery against low-temperature photoinhib ition by accelerating the recovery of the photosystem II protein compl ex.