STUDIES WITH MANGANESE-DEFICIENT SPINACH CHLOROPLASTS

1. 1. Chloroplasts were isolated from Mn2+-deficient spinach leaves and compared with chloroplasts from control plants grown for 14-19 days in water culture. The Mn2+-deficient chloroplasts contained 25% of the Mn2+ of control chloroplasts on a chlorophyll basis. 2. 2. Mn2+-deficient chloroplasts contained 1 P 700, 1 cytochrome f, 2 cytochromes b6 and 2 cytochromes 559 per 400 or so chlorophylls. Thus Mn2+ deficiency had not led to any modification of these components of the photosynthetic unit; in addition it caused no difference in carotenoid distribution. 3. 3. The Hill activities of Mn2+-deficient and control chloroplasts were saturated at the same light intensities; in the presence of an uncoupler, the light requirement was twice that required in its absence. The P e2 ratios were the same for both types of chloroplasts. Thus, Mn2+ deficiency had not caused an uncoupling of photophosphorylation from electron flow. 4. 4. Electron microscopy and freeze-etching of leaf sections showed that the lamellar structures of deficient and control chloroplasts were indistinguishable. 5. 5. Mn2+-deficient chloroplasts contained more chlorophyll b relative to chlorophyll a than control chloroplasts ( chl a chl b: control, 2.8; Mn2+-deficient, 2.2). As Mn2+ deficiency increased, there was a parallel decrease in Hill activity and in the chl a chl b ratio. The addition of Mn2+ and light to the deficient plants resulted in the restoration of Hill activity of isolated chloroplasts and the chl a chl b ratio was restored to normal. It was not possible, however, to get a similar restoration of Hill activity by the addition of Mn2+ and light to isolated deficient chloroplasts. © 1969.