Photosynthesis and photoinhibition in leaves of chlorophyll b‐less barley in relation to absorbed light

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Abstract
The response of photosynthesis to absorbed light by intact leaves of wild‐type (Hordeum vulgare L. cv. Gunilla) and chlorophyll b‐less barley (H. vulgare L. cv. Dornaria, chlorina‐f22800) was measured in a light integrating sphere. Up to the section where the light response curve bends most sharply the responses of the b‐less and wild‐type barley were similar but not identical. Average quantum yield and convexity for the mutant light response curves were 0.89 and 0.90, respectively, times those of the wild‐type barley. The maximum quantum yield for PSII photochemistry was also 10% lower as indicated by fluorescence induction kinetics (Fv/Fm). Just above the region where the light curve bends most sharply, photosynthesis decreased with time in the mutant but not in the wild‐type barley. This decrease was associated with a decrease in Fv/Fm indicating photoinhibition of PSII. This photoinhibition occurred in the same region of the light response curve where zeaxanthin formation occurs. Zeaxanthin formation occurred in both the chlorophyll b‐less and wild‐type leaves. However, the epoxidation state was lower in the mutant than in the wild‐type barley. The results indicate that chlorophyll b‐less mutants will have reduced photosynthetic production as a result of an increased sensitivity to photoinhibition and possibly a lowered quantum yield and convexity in the absence of photoinhibition.

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