Ultrastructure of chloroplast membranes in leaves of maize and ryegrass as revealed by selective staining methods

Leaves of Lolium multiflorum Lam. and Zea mays L. of different ages were prepared for TEM by a number of cytochemical methods. After post-fixation in potassium ferricyanide with osmium tetroxide the peripheral reticulum in both mesophyll and bundle sheath chloroplasts of maize stain very clearly. Post-fixation with uranyl acetate, copper and lead salts also stains the chloroplast envelope rather than the internal thylakoid system. Differences between the mesophyll and bundle sheath chloroplasts of maize and between those of ryegrass are revealed after post-fixation in zinc iodide with osmium tetroxide. After post-fixation in potassium iodide with osmium tetroxide the loculi stain less intensely than in zinc iodide. Malachite green added to glutaraldehyde at pH 7.0 enhances membrane staining in general and reveals large lipid drops in the stroma. At pH below 6.0 only the 'A' space is stained. The 'A' space and the loculus are stained when ethidium bromide is added to glutaraldehyde. The different reactions of the chloroplast membranes probably reflect differences in chemical composition.