Ultrastructural studies on differentiating chloroplasts in the ‘forma fuscoviridis’ of Ceratozamia mexicana Brongn.

summary Chloroplast ontogenesis has been examined ultrastructurally in leaflets of ‘forma fuscorviridis’ of Ceratozamia mexicana Brongn., a cycad displaying a dark red-brown colour in young developing leaves. In very young leaves the chloroplasts contain large paracrystalline prolamellar bodies (PLBs), widely extending thylakoid strips, starch, membrane-bounded paracrystals (MbPs) and conspicuous electron-dense plastoglobules (PGBs) densely packed around the PLBs. All these features progressively disappear as the development of the thylakoid system proceeds. In mature leaves the chloroplasts are characterized by randomly orientated grana stacks containing large numbers of thylakoids. The conspicuous presence of different membrane precursors during leaf ontogeny may be associated with the very low rate of leaf development in Ceratozamia.

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