Effects of Cadmium Nitrate on Spectral Characteristics and Light Reactions of Chloroplasts

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Abstract
In mesophyll chloroplasts from maize, photosystem (PS) II activities (2,6 dichlorophenol indophenol photoreduction and the variable fluorescence yield of chlorophyll (Chl) a) are inhibited strongly by 0.5 mM cadmium, supplied as Cd(NO3)2. However, diphenylcarbazide restores these activities suggesting that cadmium inhibits PSII activity at the oxygen evolving site between water and Y (the first secondary electron donor of PSII). PSI activity (light induced P700 oxidation) is insensitive' to cadmium. Furthermore, absorption and fluorescence studies showed that cadmium causes a 20% to 30% decrease in the total chlorophylls, 15% to 25% decrease in the ratio of Ch1 a/Chl b and a 20% to 25% decrease in the ratio of the short to the long wavelength forms of Chl a.