This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Holtum, J. A. M. Articles by Osmond, C. B. Search for Related Content PubMed PubMed Citation Articles by Holtum, J. A. M. Articles by Osmond, C. B. Agricola Articles by Holtum, J. A. M. Articles by Osmond, C. B.

Articles

Effect of Varying CO₂ Partial Pressure on Photosynthesis and on Carbon Isotope Composition of Carbon-4 of Malate from the Crassulacean Acid Metabolism Plant Kalanchoë daigremontiana Hamet et Perr. ¹

Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, Department of Environmental Biology, Research School of Biological Sciences, Australian National University, Canberra City, 2601 ACT, Australia

Intact leaves of Kalanchoë daigremontiana were exposed to CO₂ partial pressures of 100, 300, and 1000 microbars. Malic acid was extracted, purified, and degraded in order to obtain isotopic composition of carbon-1 and carbon-4. From these data, it is possible to calculate the carbon isotope composition of newly fixed carbon in malate. In all three treatments, the isotopic composition of newly introduced carbon is the same as that of the CO₂ source and is independent of CO₂ partial pressures over the range tested. Comparison with numerical models described previously (O'Leary 1981 Phytochemistry 20: 553-567) indicates that we would expect carbon 4 of malate to be 4 more negative than source CO₂ if diffusion is totally limiting or 7 more positive than source CO₂ if carboxylation is totally limiting. Our results demonstrate that stomatal aperture adjusts to changing CO₂ partial pressures and maintains the ratio of diffusion resistance to carboxylation resistance approximately constant. In this study, carboxylation and diffusion resistances balance so that essentially no fractionation occurs during malate synthesis. Gas exchange studies of the same leaves from which malate was extracted show that the extent of malate synthesis over the whole night is nearly independent of CO₂ partial pressure, although there are small variations in CO₂ uptake rate. Both the gas exchange and the isotope studies indicate that the ratio of external to internal CO₂ partial pressure is the same in all three treatments. Inasmuch as a constant ratio will result in constant isotope fractionation, this observation may explain why plants in general have fairly invariable ¹³C contents, despite growing under a variety of environmental conditions.

This article has been cited by other articles:

				J. Ceusters, A. M. Borland, E. Londers, V. Verdoodt, C. Godts, and M. P. De Proft Diel Shifts in Carboxylation Pathway and Metabolite Dynamics in the CAM Bromeliad Aechmea 'Maya' in Response to Elevated CO2 Ann. Bot., September 1, 2008; 102(3): 389 - 397. [Abstract] [Full Text] [PDF]

				H. Griffiths, A. B. Cousins, M. R. Badger, and S. von Caemmerer Discrimination in the Dark. Resolving the Interplay between Metabolic and Physical Constraints to Phosphoenolpyruvate Carboxylase Activity during the Crassulacean Acid Metabolism Cycle Plant Physiology, February 1, 2007; 143(2): 1055 - 1067. [Abstract] [Full Text] [PDF]

				K. Winter and J. A.M. Holtum How Closely Do the delta 13C Values of Crassulacean Acid Metabolism Plants Reflect the Proportion of CO2 Fixed during Day and Night? Plant Physiology, August 1, 2002; 129(4): 1843 - 1851. [Abstract] [Full Text] [PDF]