ULTRASTRUCTURAL STUDIES ON DIFFERENTIATING CHLOROPLASTS IN THE FORMA FUSCOVIRIDIS OF CERATOZAMIA-MEXICANA BRONGN

Chloroplast ontogenesis has been examined ultrastructurally in leaflet s of 'forma fuscoviridis' of Ceratozamia mexicana Brongn., a cycad dis playing a dark red-brown colour in young developing leaves. In very yo ung leaves the chloroplasts contain large paracrystalline prolamellar bodies (PLBs), widely extending thylakoid strips, starch, membrane-bou nded paracrystals (MbPs) and conspicuous electron-dense plastoglobules (PGBs) densely packed around the PLBs. All these features progressive ly disappear as the development of the thylakoid system proceeds. In m ature 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.