Structural and functional polymorphism of plastids in leaves of Clivia miniata Rgl. II. Ontogenesis of plastids in mesophyll cells and in cells surrounding vascular bundles

Abstract

In mesophyll cells and in cells adjoining vascular bundles of leaves in Clivia miniata Rgl. there occur chloroplasts differing with respect to their structure and the type of accumulated substances. Chloroplasts of mesophyll cells have a well-developed system of grana and intergrana thylakoids; within the stroma they accumulate solely inclusions of lipid character. Chloroplasts of cells surrounding the bundles are smaller than chloroplasts of mesophyll cells, have a poorly developed system of inner membranes and are able to accumulate only considerable amounts of starch. The third type of chloroplasts occurs in parenchymateous cells of the vascular part of the bundles. These chloroplasts, much smaller than those described above, have a reduced system of inner membranes and are not capable of accumulating either starch or lipid droplets. In stroma, they contain only plastoglobules. It seems probable that morphologically uniform proplastids are the precursors of all the studied types of chloroplasts. Their developmental sequence is determined by the degree of cellular differentiation, the type of cell as well as by the function it performs.