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Lipid and carotenoid metabolism associated with the structural transformations of the plastids during the ripening of Capsicum annuum fruits were studied. The early ripening stage is characterized by chloroplasts with a typical grana-intergranal structure and a highly developed peripheral reticulum. At a later stage the thylakoid system is disintegrated and replaced by non-chlorophyllous single thylakoids, derived in part from the inner envelope membrane. First, these changes coincide with a loss of galactolipids, a slow increase in phospholipid content, a decrease in the ratio galactolipids/phospholipids and in the galactosyl transferase activities on a protein basis. Second, these changes correlate with an enhanced accumulation of keto-carotenoids. When the phospholipid environment is disturbed by difluorodinitrobenzene or phospholipases, the biosynthesis of phytoene, β-carotene, and capsanthin is inhibited; phospholipase D has a greater effect. The role of a phospholipid environment in carotenoid biosynthesis is discussed. |
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