Impairment of galactolipid biosynthesis in tomato pericarp at chilling temperature

Pericarp lipids of mature-green tomato fruits of three cultivars of Lycopersicon esculentum Mill., and one of L. esculentum x pimpinellifolium were analyzed to clarify the relationship between membrane lipid composition and chilling sensitivity. Only the hybrid cultivar, 'New York 280' ('NY'), ripened normally at 20 degrees C after 16 d of chilling at 4 degrees C. At low temperature phospholipid content was maintained, while galactolipid content markedly declined in the four cultivars. Phosphatidylcholine content and the 18:3 content of phosphatidylcholine decreased slightly in 'NY' while they increased slightly in sensitive 'Early Cherry' ('EC') during chilling. Before chilling, the molar ratio of di- to monogalactosyldiacylglycerol of chilling-tolerant 'NY' was double that of the sensitive cultivars. This ratio increased only in 'NY' during chilling. Diacylglycerol content decreased at 4 degrees C, while free fatty acid content and the % of 16:0, 18:0 and 18:1 in the free fatty acid fraction increased. The low degree of unsaturation of diacylglycerol and free fatty acids suggests that they were not the products of galactolipid catabolism during chilling. Phosphatidyl-glycerol fatty acid composition was similar in the four cultivars under all treatments. Taken together, our data indicate that phosphatidylglycerol is not a factor differentiating fruit-chilling sensitivity in tomato cultivars. Galactolipid biosynthesis may be impaired at chilling temperature; sensitive steps may be the acylation of glycerol-3-phosphate and the transfer of phosphatidylcholine diglyceride moieties to monogalactosyldiacylglycerol.