Electron microscope studies on the morphogenesis of plastids

Streptomycin sulphate (2 mg/ml) did not affect the formation of proplastids or the elaboration of prolamellar bodies. The plastids of the streptomycin (SM)-treated cotyledons contained both crystalline prolamellar bodies and ribosomes, and were undistinguishable from the plastids of the water-grown cotyledon. However, plastids from dark-grown SM-treated cotyledons were no longer able to differentiate to more advanced stages of development, even after exposure to light. The plastids of light and dark-grown SM-treated cotyledons often contained prolamellar bodies and abnormal giant grana. Variegation developed in the cotyledons germinated in Hoagland's solution plus SM. The plastids in pale green tissue contained stroma-lamellae and one or two giant grana, whereas in those of pale yellow tissue, many osmiophilic globules, large vacuoles and crystal bodies were observed. It is suggested that the formation of prolamellar bodies may depend on cytoplasmic protein synthesis whereas functional stroma- and grana-lamellae may depend on protein synthesis within the plastids. The inhibitory effects of SM on protein synthesis were used as a tool to test this hypothesis. This work was carried out in the Department of Botany, University of California, Davis, by Grant-GB-11906 from National Science Foundation of U.S.A.