FUNCTIONAL AND STRUCTURAL DIFFERENCES AMONG PROPLASTIDS, AS SEEN BY IMMUNOGOLD STAINING AND ELECTRON-MICROSCOPY

The presence of granule-bound starch synthase and ribulose bisphosphate carboxylase/oxygenase in precursors to plastids in apexes of developing stolons of potatoes and in plumules of winter wheat was analyzed by immunogold staining and electron microscopy, From the labeling with gold particles of sections, the heretofore designated ''proplastid'' could be separated into at least two types; one type devoid of granule-bound starch synthase and ribulose bisphosphate carboxylase/oxygenase and the other already containing these enzymes, The immunogold staining and electron microscopy also showed that these two types of organelles contained DNA and that these two groups seemed to be developmentally related to the formation of plastids, The former type was indistinguishable from the plastid initial of wintering perennials in terms of ultrastructure and can be classified as a plastid initial, The latter type is homogeneous in terms of ultrastructure and the stage of development relative to mature plastids, and it should be referred to as a genuine proplastid.