The Isolation of Proplastids from Roots of Vicia faba.

To our knowledge most living cells in higher plants contain plastids. In nongreen tissues such as primary roots, the plastids have been identified by the rather ambiguous name "proplastids." These proplastids are generally described as rather simple organelles, bounded by a double envelope and containing only a few internal membranes with a limited number of invaginations of the inner membrane of the plastid envelope (4). Ribosomes also apparently occur in proplastids (6) and depending on where the proplastids occur in the root the organelles may contain starch grains (3, 6). Proplastids in some roots are somewhat more complex in that they store protein and tubular complexes of membranes occur (6). However, the prefix "pro" might imply that proplastids have limited functional significances in the growth, development, and metabolism of root cells and are primarily latent progenitors of other types of plastid of more functional significance in the plant. There is almost no direct information on the biochemical properties and functional roles of proplastids in tissues such as roots. The present paper reports a method for the isolation of proplastids from roots of Vicia faba. Electron microscopical examination of the isolated fraction revealed that it contained numerous proplastids in an excellent state of preservation, substantially freed from cellular contamination, and thus would provide good starting material for the investigation of the properties of proplastids.