Electron Microscopic Evidence for Membrane Bound Structures in Plant Vacuoles
To date, most electron microscope studies of mature plant tissue have shown the vacuole to be generally devoid of internal structure except for irregular aggregates of electron dense granular material. However, after gluturaldehyde-osmium fixation, membrane bound structures are frequently observed in the vacuoles of the mesophyll cells of the xerophytic plant, Tamarix (Fig. 1). These structures are generally ovoid in shape and range in length from .5 to 1.6 μ.Some of the membrane bound, vacuolar inclusions are bounded by two membranes which are often tightly opposed (Fig. 2, arrow). Other inclusions are bounded by a single tripartate membrane (Fig. 3). The internal organization of the inclusions consists of tubules surrounded by an electron-translucent matrix (Fig. 2 & 3). The tubules measure about 350 A in diameter and frequently extend in arrays parallel to the bounding membrane. Occasionally vesicles about 1000 A in diameter are also observed in the inclusions (Fig. 1).