Abstract
The ripening process in fruits ofA. commutatum is characterized by clearly distinguishable developmental stages of their pericarp plastids. With respect to predominant pigments and ultrastructural features the following scheme is proposed: 1. The green stage with a tendency to thylakoid degeneration and plastoglobule formation leads to 2. the yellow stage. An increasing number of globules, mostly being membrane associated, are converted to tubules. In this stage, the main pigments are β-carotene and cryptoxanthine. The development of membraneous invaginations from the inner plastid envelope leads to 3. the red stage. Concomitantly with lycopene synthesis and incorporation, these envelope-derived membranes expand and become electron dense (after KMnO4 treatment), but maintain their triple-layered structure. Chromoplasts of deep red coloured fruits (1,400 μg lycopene g−1 dry wt) contain lycopene crystals within the lumina of membraneous sacs which are also derived from the inner envelope membrane. The molar ratio between the three main pigments β-carotene, cryptoxanthine, and lycopene is about 1∶1∶10 in this final state. GA/OsO4 fixation is unable to stabilize the “lycopenic” structures (membranes as well as crystals).
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