Lipid Transformations in Plastids of Bean Leaves and Pepper Fruits

A few reports have appeared concerning the synthesis of plastid lipids. Stumpf and James (17) and Stumpf et al. (18) found that both saturated and unsaturated fatty acids may be formed from acetate by chloroplast preparations. However, in some bluegreen algae, Bloch et al. (4) found that long-chain monounsaturates are synthesized by oxidative desaturation of corresponding saturates. Kates (9) suggested that C14 incorporation into the galactose moiety of galactolipids occurs by the conversion of glucose to UDP-glucose and by the subsequent formation of UDP-galactose. Apparently the galactolipids are rapidly labeled with C14 during photosynthesis with C14O_, whereas phosphatidyl glycerol is less rapidly labeled (3). Further, some details are known about the in vitro breakdown of plastid lipids or the presence of enzymic systems which cause the breakdown of plastid lipids (7, 16,21). However, few investigations have been concerned with the in vivo degradation of plastid lipids or with the lipids of senescent plastids. Two tissues in which plastid breakdown may occur were selected for this study. Mature leaves grown under a 20 hour per 24 hour photoperiod were placed in continuous darkness following which plastids were isolated. The plastids from ripening pepper fruits were also isolated. For comparison, the plastid lipids of leaves subjected to 3 different lengths of darkness and plastid lipids from pepper fruits at 3 stages of maturity were investigated.