ELECTRON MICROSCOPE STUDY OF ORIGIN AND DEVELOPMENT OF VACUOLES IN ROOT-TIP CELLS OF LUPINUS ALBUS L

The origin and the evolution of the vacuolar system were studied in the roots of Lupinus albus L. fixed by glutaraldehyde-OsO4. In the meristematic cells, the rough ER dilates to form vesicles (provacuoles) that may be either terminal or intercalated. In more differentiated cells, the vacuoles are similar to these vesicles, but larger, and frequently they show prolongations indistinguishable from profiles of the rough ER. The vacuolar membrane (tonoplast) is continuous with the external membrane of the nuclear envelope, which results in a direct communication between the intravacuolar space and the perinuclear cisterna. On the other hand, the vacuolar membrane and the plasmalemma appear to be merely contiguous. In a more advanced stage of differentiation the membranes from adjacent vacuoles fuse to form the large vacuole characteristic of the parenchymatous cell. The results are in general agreement with those reported by Buvat and Poux. © 1969 Academic Press, Inc.