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Plant Physiology 58:552-555 (1976)
© 1976 American Society of Plant Biologists

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Differential Oxygen Response of Photosynthesis in Soybean and Panicum milioides

Robert W. Kecka,1

William L. Ogrenb

a Department of Agronomy, University of Illinois, Urbana, Illinois 61801, b Agricultural Research Service, United States Department of Agriculture, Urbana, Illinois 61801

The carbon dioxide compensation concentration of Panicum milioides was less than that of soybean over the range of 15 to 35 C. In soybean (Glycine max [L.] Merr. cv. Wayne), the compensation concentration was directly proportional to O2 concentration. In P. milioides, the compensation concentration was near zero up to 10% O2 and then increased linearly with higher O2, although the slope of the response was less than that in soybean. Leaf extracts of P. milioides contained 3-fold higher phosphoenolpyruvate carboxylase activity than soybean leaf extracts. Oxygen inhibition of photosynthesis and carboxy-lation efficiency was less in P. milioides than that observed in soybean. The affinity of P. millioides ribulose-1,5-di-P carboxylase for CO2 appeared to be slightly greater than that of soybean. The affinity of both enzymes for O2 was similar. The reduced response of the compensation concentration and photosynthesis to O2 in P. milioides may be explained by photosynthetic phosphoenolpyruvate carboxylase fixation and by an apparent increased affinity of ribulose-1,5-di-P carboxylase for CO2.

1 Permanent address: Department of Biology, Indiana University-Purdue University at Indianapolis, Indiana 46205.






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Copyright © 1976 by the American Society of Plant Biologists