Compensation Point and Isotopic Characteristics of C3/C4 Intermediates and Hybrids in Panicum

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Abstract
Leaf CO2 compensation points and stable hydrogen, oxygen and carbon isotope ratios were determined for Panicum species including C3/C4 intermediate photosynthesis plants, hybrids between C3/C4 intermediates and C3 plants, C3 and C4 plants in the Panicum genus as well as several other C3 and C4 plants. C3 plants had the highest compensation points, followed by hybrids, C3/C4 intermediates, and C4 plants. .delta.13C values of cellulose nitrate and saponifiable lipids from C4 plants were about 10.permill. higher than those observed for cellulose nitrate and saponifiable lipids of C3/C4 intermediates, hybrids, and C3 plants. Oxygen isotope ratios of cellulose as well as those of leaf water were similar for all plants. There was substantial variability in the .delta.D values of cellulose nitrate among the plants studied. In contrast, such variability was not observed in .delta.D values of water distilled from the leaves, nor in the .delta.D values of the saponifiable lipids. Variability in .delta.D values of cellulose nitrate from C3/C4 intermediates, hybrids, C3, and C4 plants is due to fractionations occurring during biochemical reactions specific to leaf carbohydrate metabolism.