The fluorescence properties of manganese-deficient spinach chloroplasts

Abstract

The fluorescence properties of chloroplasts from Mn-deficient and control spinach plants were studied at 20°C and 77°K, using light of weak intensities for excitation. 1. 1. At 20°C, the quantum yields of fluorescence of the Mn-deficient chloroplasts exceeded those of the control; at 77°K the position was reversed. 2. 2. A comparison of the induction of fluorescence intensity at 20°C showed that the increase from the initial fluorescence to the final steady-state was much lower with the Mn-deficient chloroplasts and they showed a faster induction rate. 3. 3. The fluorescence yields of Mn-deficient chloroplasts in the presence and absence of a Hill oxidant were comparable, whereas with control chloroplasts the fluorescence yield was lower under oxidizing conditions. The fluorescence yields of both types of chloroplasts under reducing conditions were similar. 4. 4. At 77°K, the 693-mμ fluorescence emission band was absent from the Mn-deficient spectrum. Some 80% of the total fluorescence was emitted at 735 mμ for the Mn-deficient chloroplasts as compared to 70% for the control. 5. 5. The effect of DCMU on fluorescence yields was similar to Mn deficiency. At 77°K with DCMU-inhibited chloroplasts, the 683-mμ and 693-mμ emission bands relative to 735 mμ were lower, although not as low as that of Mn-deficient ones; some 74% of the total fluorescence was emitted at 735 mμ. 6. 6. It appears that Mn deficiency causes a block between the primary and secondary reductants of Photosystem 2.