[Electron microscope studies on the crystal-like structures in the plastid stroma].

The crystal-like structures in the plastid stroma of primary leaves of Phaseolus vulgaris, recently described by several authors, were studied with the electron microscope after different treatments: 1. The crystal-like structures can be seen after fixation in glutaraldehyde followed by a post-fixation with osmium tetroxide as well as after osmium tetroxide fixation alone. They are not preserved by fixation in permanganate. 2. After double-staining with uranyl acetate and lead citrate the electron-opacity of the filaments which compose the crystal-like body is selectively enhanced. This phenomenon does not occur after single-staining with lead citrate. 3. When de-osmicated sections are treated with pepsin the substance of the crystal-like bodies is selectively digested, whereas this substance does not disappear after treatment with RNase. 4. When pieces of leaves are kept floating on a sucrose solution the number of the crystal-like bodies is markedly increased. These results taken together seem to constitute evidence that the crystal-like bodies represent a store of protein.Some micrographs of small crystal-like bodies indicate that the straight filaments represent arrangements of globular subunits with diameters of about 5 nm.In a great many plastids some structures other than these crystal-like bodies are seen which seem to correspond to the "stromacentres" reported by GUNNING (1965). Intermediates between this stromacentre-like type with curved filaments and the above mentioned crystal-like type with straight filaments can be observed.