Abstract
Leaves of maize (Zea mays L.) were enclosed in a temperature-controlled cuvette under 35 Pa (350 [mu]bars) CO2 and 0.2 kPa (0.2%)O2 and exposed to short periods (1-30 s) of illumination (light-flecks). The rate and total amount of CO2 assimilated and O2 evolved were measured. The O2 evolution rate was taken as an indicator of the rate of photosynthetic noncyclic electron transport (NCET). In this C4 species, the response of electron transport during the lightflecks qualitatively mimicked that of C3 species previously tested, whereas the response of CO2 assimilation differed. Under short-duration lightflecks at high photon flux density (PFD), the mean rate of O2 evolution was greater than the steady-state rate of O2 evolution under the same PFD due to a burst of O2 evolution at the beginning of the lightfleck. This O2 burst was taken as indicating a high level of NCET involved in the buildup of assimilatory charge via ATP, NADPH, and reduced or phosphorylated metabolites. However, as lightfleck duration decreased, the amount of CO2 assimilated per unit time of the lightfleck (the mean rate of CO2 assimilation) decreased. There was also a burst of CO2 from the leaf at the beginning of low-PFD lightflecks that further reduced the assimilation during these lightflecks. The results are discussed in terms of the buildup of assimilatory charge through the synthesis of high-energy metabolites specific to C4 metabolism. It is speculated that the inefficiency of carbon uptake during brief light transients in the C4 species, relative to C3 species, is due to the futile synthesis of C4 cycle intermediates.
Full Text
The Full Text of this article is available as a PDF (595.2 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Johnson H. S., Hatch M. D. Properties and regulation of leaf nicotinamide-adenine dinucleotide phosphate-malate dehydrogenase and 'malic' enzyme in plants with the C4-dicarboxylic acid pathway of photosynthesis. Biochem J. 1970 Sep;119(2):273–280. doi: 10.1042/bj1190273. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Karabourniotis G., Manetas Y., Gavalas N. A. Photoregulation of Phosphoenolpyruvate Carboxylase in Salsola soda L. and Other C(4) Plants. Plant Physiol. 1983 Nov;73(3):735–739. doi: 10.1104/pp.73.3.735. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Nakamoto H., Edwards G. E. Influence of Oxygen and Temperature on the Dark Inactivation of Pyruvate, Orthophosphate Dikinase and NADP-Malate Dehydrogenase in Maize. Plant Physiol. 1983 Mar;71(3):568–573. doi: 10.1104/pp.71.3.568. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sharkey T. D., Seemann J. R., Pearcy R. W. Contribution of Metabolites of Photosynthesis to Postillumination CO(2) Assimilation in Response to Lightflects. Plant Physiol. 1986 Dec;82(4):1063–1068. doi: 10.1104/pp.82.4.1063. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Shieh Y. J., Ku M. S., Black C. C. Photosynthetic Metabolism of Aspartate in Mesophyll and Bundle Sheath Cells Isolated from Digitaria sanguinalis (L.) Scop., a NADP-Malic Enzyme C(4) Plant. Plant Physiol. 1982 Apr;69(4):776–780. doi: 10.1104/pp.69.4.776. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Usuda H. Changes in Levels of Intermediates of the C(4) Cycle and Reductive Pentose Phosphate Pathway during Induction of Photosynthesis in Maize Leaves. Plant Physiol. 1985 Aug;78(4):859–864. doi: 10.1104/pp.78.4.859. [DOI] [PMC free article] [PubMed] [Google Scholar]