Electron Microscope Studies on the Morphogenesis of Plastids

Comparisons of the ultrastructure of plastids in three kinds of variegated leaves of tomato plants were made. No difference in the structure and development of chloroplasts in normal green leaves and in the green tissue of variegated leaves was found. The albescent tissues of chromosomal genetic variegated leaves contained only aberrant plastids, which were amoeboid or cup-shaped and had large vacuoles in the stroma. Ribosomes were absent from all plastids in this kind of variegated leaves. Three types of plastids, i.e. chloroplasts containing grana, chloroplasts lacking grana, and plastids lacking internal membranes, were present in the pale green tissues of the variegated leaves of extrachromosomal genetic tomato mutants. Depending on the distribution of these plastids, five cell types were observed in these tissues. Ribosomes were present in all plastids in this type of variegated leaves. In the albescent tissues of variegated leaves induced by streptomycin treatment, two kinds of plastids were observed, one containing giant grana and the other lacking organized internal membranes. A common feature of plastids in this albescent tissue was the presence of light stainable ribosomes. It was suggested that the development of variegated leaves may be caused by blocking an early stage of plastid development.