Abstract
It was previously shown with concurrent measurements of gas exchange and carbon isotope discrimination that the reduction of ribulose-1,5-bisphosphate carboxylase/oxygenase by an antisense gene construct in transgenic Flaveria bidentis (a C4 species) leads to reduced CO2 assimilation rates, increased bundle-sheath CO2 concentration, and leakiness (defined as the ratio of CO2 leakage to the rate of C4 acid decarboxylation; S. von Caemmerer, A. Millegate, G.D. Farquhar, R.T. Furbank [1997] Plant Physiol 113: 469-477). Increased leakiness in the transformants should result in an increased ATP requirement per mole of CO2 fixed and a change in the ATP-to-NADPH demand. To investigate this, we compared measurements of the quantum yield of photosystem I and II ([phi]PSI and [phi]PSII) with the quantum yield of CO2 fixation ([phi]CO2) in control and transgenic F. bidentis plants in various conditions. Both [phi]PSI/[phi]CO2 and [phi]PSII/[phi]CO2 increased with a decrease in ribulose-1,5-bisphosphate carboxylase/oxygenase content, confirming an increase in leakiness. In the wild type the ratio of [phi]PSI to [phi]PSII was constant at different irradiances but increased with irradiance in the transformants, suggesting that cyclic electron transport may be higher in the transformants. To evaluate the relative contribution of cyclic or linear electron transport to extra ATP generation, we developed a model that links leakiness, ATP/NADP requirements, and quantum yields. Despite some uncertainties in the light distribution between photosystem I and II, we conclude from the increase of [phi]PSII/[phi]CO2 in the transformants that cyclic electron transport is not solely responsible for ATP generation without NADPH production.
Full Text
The Full Text of this article is available as a PDF (1.2 MB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Ausenhus S. L., O'Leary M. H. Hydrolysis of phosphoenolpyruvate catalyzed by phosphoenolpyruvate carboxylase from Zea mays. Biochemistry. 1992 Jul 21;31(28):6427–6431. doi: 10.1021/bi00143a010. [DOI] [PubMed] [Google Scholar]
- Butz N. D., Sharkey T. D. Activity ratios of ribulose-1,5-bisphosphate carboxylase accurately reflect carbamylation ratios. Plant Physiol. 1989 Mar;89(3):735–739. doi: 10.1104/pp.89.3.735. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Furbank R. T., Badger M. R., Osmond C. B. Photoreduction of oxygen in mesophyll chloroplasts of c(4) plants: a model system for studying an in vivo mehler reaction. Plant Physiol. 1983 Dec;73(4):1038–1041. doi: 10.1104/pp.73.4.1038. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Furbank R. T., Chitty J. A., Von Caemmerer S., Jenkins CLD. Antisense RNA Inhibition of RbcS Gene Expression Reduces Rubisco Level and Photosynthesis in the C4 Plant Flaveria bidentis. Plant Physiol. 1996 Jul;111(3):725–734. doi: 10.1104/pp.111.3.725. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Mate C. J., Hudson G. S., von Caemmerer S., Evans J. R., Andrews T. J. Reduction of ribulose biphosphate carboxylase activase levels in tobacco (Nicotiana tabacum) by antisense RNA reduces ribulose biphosphate carboxylase carbamylation and impairs photosynthesis. Plant Physiol. 1993 Aug;102(4):1119–1128. doi: 10.1104/pp.102.4.1119. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Mitchell P. Vectorial chemiosmotic processes. Annu Rev Biochem. 1977;46:996–1005. doi: 10.1146/annurev.bi.46.070177.005024. [DOI] [PubMed] [Google Scholar]
- Von Caemmerer S., Millgate A., Farquhar G. D., Furbank R. T. Reduction of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase by Antisense RNA in the C4 Plant Flaveria bidentis Leads to Reduced Assimilation Rates and Increased Carbon Isotope Discrimination. Plant Physiol. 1997 Feb;113(2):469–477. doi: 10.1104/pp.113.2.469. [DOI] [PMC free article] [PubMed] [Google Scholar]