The Effect of Manganese Deficiency on the Structure of Spinach Chloroplasts

Manganese is involved in the photosynthetic reactions of algae and leaves of higher plants (1-3). In tomato, manganese deficiency results in chloroplasts with a greatly reduced Hill reaction activity per unit chlorophyll (3). In spinach, manganese deficiency causes a 50 to 70 per cent reduction in the FMN-mediated photophosphorylation of isolated chloroplasts but only slightly affects the phosphorylation mediated by pyocyanine (4). Manganese is a constituent of the chloroplasts of higher plants. Photochemical activity of isolated chloroplasts is closely correlated with manganese content, and the manganese important in these reactions is not free ionic manganese but that bound within the chloroplast (5). This paper reports the effects of manganese deficiency on the structure of spinach chloroplasts. Manganese-deficient spinach plants (Spinacia oleracea L.) grown in nutrient culture solutions (3) were harvested together with healthy control plants when the leaves were showing a mild chlorosis. Small portions of the leaf were infiltered with 0.3 M sucrose, sections were cut free hand, and the living leaf cells examined by light microscopy. Samples were fixed in KMnO4 (6) for electron microscope observations. In living tissue manganese deficient cells contain a considerably reduced number of chloroplasts. These are char-acterised by dark regions which fluoresce strongly under the fluorescence microscope, and are therefore regions of chlorophyll concentration (Fig. 2), whereas chloroplasts from normal leaves contain numerous, well defined grana which fluoresce strongly under the fluorescence microscope (Fig. 1). The basic ultrastructure of normal spinach chloroplasts (Fig. 3) is essentially similar to that reported for Zea mays (6), sorghum (7), and tobacco (8). The chloroplasts are seen to contain a well defined system of lamellae differentiated into grana and intergrana regions. Stroma is present between the intergrana lamellae, but does not penetrate into the grana. The chloroplast is always enclosed by a membrane. Stroma material may form a wide band between the lamellae and the membrane, or form pseudopodia-like extensions devoid of lamellae, but enclosed by the membrane. In chloroplasts from slightly deficient plants the intergrana lamellae are seen to be detached from the grana and lie scattered throughout the stroma, but the grana are more or less normal. With increasing severity of deficiency, fewer intergrana lamellae are present and some of these fuse end-to-end to give vesicles. "Empty" regions appear in the stroma. The grana are abnormal, tend to be elliptical in shape, and the individual lamellar discs tend to be separate. In more severe deficiency, …