LIPID-COMPOSITION AND BIOSYNTHESIS IN PROTOPLASTS FROM CUCUMBER COTYLEDONS

The lipid composition and lipid metabolism of protoplasts isolated fro m cucumber (Cucumis sativus) cotyledons were examined. Comparisons wer e made of the fresh tissue, tissue which had been incubated in the pro toplasting medium without the digestive enzymes, the freshly prepared protoplasts and protoplasts conditioned by storage for 8 hr at 27-degr ees. Triacylglycerols (25%), monogalactosyldiacylglycerols (38%) and p hosphatidylcholine (21%) accounted for most of the lipid in the fresh tissue. In the freshly prepared protoplasts these percentages were, re spectively, 51, 21 and 8. The fatty acid compositions of these lipids were somewhat changed in the freshly prepared protoplasts. There were decreases in 18:3 in phosphatidylglycerol and phosphatidylethanolamine , and decreases in 18:2 in digalactosyldiacylglycerol and phosphatidyl choline. Incorporation of C-14-acetate for 1 hr in the fresh tissue wa s mainly into phosphatidylglycerol (22.2%), phosphatidylcholine (19.2% ) and triacylglycerols+diacylglycerols (14.5%). In freshly isolated pr otoplasts these figures were 16.5, 43.2 and 21.5%, respectively. Incor poration of C-14-bicarbonate for 1 hr was 22.5% into triacylglycerols + diacylglycerols 3.7% into phosphatidylglycerol and 5.5% into phospha tidylcholine in the fresh tissue. In freshly prepared protoplasts the values were 25.6, 12.4 and 22.5%, respectively. Changes in the lipid c omposition and metabolism of conditioned protoplasts compared to fresh ly prepared protoplasts, which are more sensitive to chilling, did not suggest any relationship to chilling injury.