Abstract
C4 leaf phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31) is subject to a day/night regulatory phosphorylation cycle. By using the cytoplasmic protein synthesis inhibitor cycloheximide (CHX), we previously reported that the reversible in vivo light activation of the C4 PEPC protein-serine kinase requires protein synthesis. In the present leaf gas-exchange study, we have examined how and to what extent the CHX-induced inhibition of PEPC protein kinase activity/PEPC phosphorylation in the light influences C4 photosynthesis. Detached Sorghum vulgare and maize (Zea mays) leaves fed 10 [mu]M CHX showed a gradual but marked decrease in photosynthetic CO2 assimilation capacity. A series of control experiments designed to assess deleterious secondary effects of the inhibitor established that this reduction in C4 leaf CO2 assimilation was not due to (a) an increased stomatal resistance to CO2 diffusion, (b) a decrease in the activation state of other photoactivated C4 cycle enzymes, and (c) a perturbation of the Benson-Calvin C3 cycle, as evidenced by the absence of an inhibitory effect of CHX on leaf photosynthesis by a C3 grass (Triticum aestivum). It is notable that the CHX-induced decrease in CO2 assimilation by illuminated Sorghum leaves was highly correlated with a decrease in the apparent phosphorylation status of PEPC and a concomitant change in carbon isotope discrimination consistent with a shift from a C4 to a C3 mode of leaf CO2 fixation. These collective findings indicate that the light-dependent activation of the PEPC protein-serine kinase and the resulting phosphorylation of serine-8 or serine-15 in Sorghum or maize PEPC, respectively, are fundamental regulatory events that influence leaf C4 photosynthesis in vivo.
Full Text
The Full Text of this article is available as a PDF (739.5 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Bakrim N., Echevarria C., Cretin C., Arrio-Dupont M., Pierre J. N., Vidal J., Chollet R., Gadal P. Regulatory phosphorylation of Sorghum leaf phosphoenolpyruvate carboxylase. Identification of the protein-serine kinase and some elements of the signal-transduction cascade. Eur J Biochem. 1992 Mar 1;204(2):821–830. doi: 10.1111/j.1432-1033.1992.tb16701.x. [DOI] [PubMed] [Google Scholar]
- Bowman W. D., Hubick K. T., von Caemmerer S., Farquhar G. D. Short-term changes in leaf carbon isotope discrimination in salt- and water-stressed c(4) grasses. Plant Physiol. 1989 May;90(1):162–166. doi: 10.1104/pp.90.1.162. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Echevarría C., Vidal J., Jiao J. A., Chollet R. Reversible light activation of the phosphoenolpyruvate carboxylase protein-serine kinase in maize leaves. FEBS Lett. 1990 Nov 26;275(1-2):25–28. doi: 10.1016/0014-5793(90)81430-v. [DOI] [PubMed] [Google Scholar]
- Jiao J. A., Chollet R. Light activation of maize phosphoenolpyruvate carboxylase protein-serine kinase activity is inhibited by mesophyll and bundle sheath-directed photosynthesis inhibitors. Plant Physiol. 1992 Jan;98(1):152–156. doi: 10.1104/pp.98.1.152. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Jiao J. A., Chollet R. Posttranslational regulation of phosphoenolpyruvate carboxylase in c(4) and crassulacean Acid metabolism plants. Plant Physiol. 1991 Apr;95(4):981–985. doi: 10.1104/pp.95.4.981. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Jiao J. A., Chollet R. Regulatory phosphorylation of serine-15 in maize phosphoenolpyruvate carboxylase by a C4-leaf protein-serine kinase. Arch Biochem Biophys. 1990 Dec;283(2):300–305. doi: 10.1016/0003-9861(90)90646-g. [DOI] [PubMed] [Google Scholar]
- Jiao J., Echevarría C., Vidal J., Chollet R. Protein turnover as a component in the light/dark regulation of phosphoenolpyruvate carboxylase protein-serine kinase activity in C4 plants. Proc Natl Acad Sci U S A. 1991 Apr 1;88(7):2712–2715. doi: 10.1073/pnas.88.7.2712. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Nakamoto H., Edwards G. E. Light Activation of Pyruvate,Pi Dikinase and NADP-Malate Dehydrogenase in Mesophyll Protoplasts of Maize : Effect of DCMU, Antimycin A, CCCP, and Phlorizin. Plant Physiol. 1986 Sep;82(1):312–315. doi: 10.1104/pp.82.1.312. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Prioul J. L., Brangeon J., Reyss A. Interaction between External and Internal Conditions in the Development of Photosynthetic Features in a Grass Leaf: II. REVERSIBILITY OF LIGHT-INDUCED RESPONSES AS A FUNCTION OF DEVELOPMENTAL STAGES. Plant Physiol. 1980 Oct;66(4):770–774. doi: 10.1104/pp.66.4.770. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Wang Y. H., Duff S. M., Lepiniec L., Crétin C., Sarath G., Condon S. A., Vidal J., Gadal P., Chollet R. Site-directed mutagenesis of the phosphorylatable serine (Ser8) in C4 phosphoenolpyruvate carboxylase from sorghum. The effect of negative charge at position 8. J Biol Chem. 1992 Aug 25;267(24):16759–16762. [PubMed] [Google Scholar]