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Photosynthesis of F₁ Hybrids between C₄ and C₃-C₄ Species of Flaveria¹

Department of Agronomy, University of Georgia, Athens, Georgia 30602, Department of Biochemistry, University of Georgia, Athens, Georgia 30602, Richard Russell Research Center, United States Department of Agriculture, Agricultural Research Service, Athens, Georgia, Department of Biology, University of Miami, Coral Gables, Florida 33124, Department of Earth and Space Sciences and Archaeology Program, University of California, Los Angeles, California 90024

Photosynthetic characteristics were studied in several F₁ hybrids between C₄ and C₃-C₄ species of Flaveria. Stable carbon isotope ratios, O₂ inhibition of apparent photosynthesis, and phosphoenolpyruvate carboxylase activities in the hybrids were similar to the means for the parents. Values of CO₂ compensation concentrations were nearer to those of the C₄ parent and apparent photosynthesis was below that of both parents, being only 60 and 74% of that of the lowest (C₃-C₄) parent in two experiments. Reductions of CO₂ compensation concentration and O₂ inhibition of apparent photosynthesis as well as increases in carbon isotope ratios and phosphoenolpyruvate carboxylase activities compared to values in C₃-C₄ species suggest transfer of a limited degree of C₄ photosynthesis to the F₁ hybrids. However, the lower apparent photosynthesis of the hybrids suggests that transfer of C₄ characteristics to non-C₄ species is detrimental unless characteristics associated with C₄ photosynthesis are fully developed. There was a highly significant negative correlation (r = –0.90) between CO₂ compensation concentration and the logarithm of phosphoenolpyruvate carboxylase activity in the parents and hybrids, suggesting involvement of this enzyme in controlling the CO₂ compensation concentration. Although bundle-sheath cells were more developed in leaves of hybrids than in C₃-C₄ parents, they appeared to contain lower quantities of organelles than those of the C₄ parent. Reduced quantities of organelles in bundle-sheath cells could indicate incomplete compartmentation of partial pathways of the C₄ cycle in the hybrids. This may mean that the reduction of CO₂ compensation and O₂ inhibition of apparent photosynthesis relative to the C₃-C₄ parents is less dependent on fully developed Kranz anatomy than is increased apparent photosynthesis.

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				A. D. McKown, J.-M. Moncalvo, and N. G. Dengler Phylogeny of Flaveria (Asteraceae) and inference of C4 photosynthesis evolution Am. J. Botany, November 1, 2005; 92(11): 1911 - 1928. [Abstract] [Full Text] [PDF]