Photosynthetic and Photorespiratory Characteristics of Mutants of Hordeum vulgare L

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Abstract
The relationship between photosynthesis and photorespiration was determined in normal and 26 mutants of barley (H. vulgare L. var. Himalaya). The rate of apparent photosynthesis ranged from 1-30 mg of CO2/square decimeter per h. The variation in rate of photosynthesis was due, in some cases, to difference in chlorophyll content, in others to stomatal resistance and in still others to unknown factors; but no single factor accounted for the variation. Photorespiratory activity, as determined by the 14CO2/12CO2 technique, CO2 evolution into CO2-free air and the response of photosynthesis to low and high O2 concentrations, was positively and significantly correlated with photosynthesis. This supports the idea that the 2 processes are integrally and tightly coupled. There appears to be no competition between photosynthesis and photorespiration and the probability of finding plants with high rates of photosynthesis and low rates of photorespiration measured under natural conditions, appears to be very low.