Abstract
Despite previous reports of no apparent photorespiration in C4 plants based on measurements of gas exchange under 2 versus 21% O2 at varying [CO2], photosynthesis in maize (Zea mays) shows a dual response to varying [O2]. The maximum rate of photosynthesis in maize is dependent on O2 (approximately 10%). This O2 dependence is not related to stomatal conductance, because measurements were made at constant intercellular CO2 concentration (Ci); it may be linked to respiration or pseudocyclic electron flow. At a given Ci, increasing [O2] above 10% inhibits both the rate of photosynthesis, measured under high light, and the maximum quantum yield, measured under limiting light ([phi]CO2). The dual effect of O2 is masked if measurements are made under only 2 versus 21% O2. The inhibition of both photosynthesis and [phi]CO2 by O2 (measured above 10% O2) with decreasing Ci increases in a very similar manner, characteristically of O2 inhibition due to photorespiration. There is a sharp increase in O2 inhibition when the Ci decreases below 50 [mu]bar of CO2. Also, increasing temperature, which favors photorespiration, causes a decrease in [phi]CO2 under limiting CO2 and 40% O2. By comparing the degree of inhibition of photosynthesis in maize with that in the C3 species wheat (Triticum aestivum) at varying Ci, the effectiveness of C4 photosynthesis in concentrating CO2 in the leaf was evaluated. Under high light, 30[deg]C, and atmospheric levels of CO2 (340 [mu]bar), where there is little inhibition of photosynthesis in maize by O2, the estimated level of CO2 around ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in the bundle sheath compartment was 900 [mu]bar, which is about 3 times higher than the value around Rubisco in mesophyll cells of wheat. A high [CO2] is maintained in the bundle sheath compartment in maize until Ci decreases below approximately 100 [mu]bar. The results from these gas exchange measurements indicate that photorespiration occurs in maize but that the rate is low unless the intercellular [CO2] is severely limited by stress.
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Selected References
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- Dai Z., Edwards G. E., Ku M. S. Control of Photosynthesis and Stomatal Conductance in Ricinus communis L. (Castor Bean) by Leaf to Air Vapor Pressure Deficit. Plant Physiol. 1992 Aug;99(4):1426–1434. doi: 10.1104/pp.99.4.1426. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Ehleringer J., Björkman O. Quantum Yields for CO(2) Uptake in C(3) and C(4) Plants: Dependence on Temperature, CO(2), and O(2) Concentration. Plant Physiol. 1977 Jan;59(1):86–90. doi: 10.1104/pp.59.1.86. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Furbank R. T., Hatch M. D. Mechanism of c(4) photosynthesis: the size and composition of the inorganic carbon pool in bundle sheath cells. Plant Physiol. 1987 Dec;85(4):958–964. doi: 10.1104/pp.85.4.958. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Jenkins C. L., Furbank R. T., Hatch M. D. Mechanism of c(4) photosynthesis: a model describing the inorganic carbon pool in bundle sheath cells. Plant Physiol. 1989 Dec;91(4):1372–1381. doi: 10.1104/pp.91.4.1372. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Jordan D. B., Ogren W. L. Species variation in kinetic properties of ribulose 1,5-bisphosphate carboxylase/oxygenase. Arch Biochem Biophys. 1983 Dec;227(2):425–433. doi: 10.1016/0003-9861(83)90472-1. [DOI] [PubMed] [Google Scholar]
- Krömer S., Heldt H. W. On the Role of Mitochondrial Oxidative Phosphorylation in Photosynthesis Metabolism as Studied by the Effect of Oligomycin on Photosynthesis in Protoplasts and Leaves of Barley (Hordeum vulgare). Plant Physiol. 1991 Apr;95(4):1270–1276. doi: 10.1104/pp.95.4.1270. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Marek L. F., Stewart C. R. Photorespiratory glycine metabolism in corn leaf discs. Plant Physiol. 1983 Sep;73(1):118–120. doi: 10.1104/pp.73.1.118. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Ziem-Hanck U., Heber U. Oxygen requirement of photosynthetic CO2 assimilation. Biochim Biophys Acta. 1980 Jul 8;591(2):266–274. doi: 10.1016/0005-2728(80)90158-9. [DOI] [PubMed] [Google Scholar]
- de Veau E. J., Burris J. E. Photorespiratory rates in wheat and maize as determined by o-labeling. Plant Physiol. 1989 Jun;90(2):500–511. doi: 10.1104/pp.90.2.500. [DOI] [PMC free article] [PubMed] [Google Scholar]