Abstract
CO2 uptake rate, chlorophyll fluorescence, and 830-nm absorbance were measured in wild-type (wt) Nicotiana sylvestris (Speg. et Comes) and starchless mutant NS 458 leaves at different light intensities and CO2 concentrations. Initial slopes of the relationships between CO2 uptake and light and CO2 were similar, but the maximum rate at CO2 and light saturation was only 30% in the mutant compared with the wt. O2 enhancement of photosynthesis at CO2 and light saturation was relatively much greater in the mutant than in the wt. In 21% O2, the electron transport rate (ETR) calculated from fluorescence peaked near the beginning of the CO2 saturation of photosynthesis. With the further increase of CO2 concentration ETR remained nearly constant or declined a little in the wt but drastically declined in the mutant. Absorbance measurements at 830 nm indicated photosystem I acceptor side reduction in both plants at saturating CO2 and light. Assimilatory charge (postillumination CO2 uptake) measurements indicated trapping of chloroplast inorganic phosphate, supposedly in hexose phosphates, in the mutant. It is concluded that starch synthesis gradually substitutes for photorespiration as electron acceptor with increasing CO2 concentration in the wt but not in the mutant. It is suggested that starch synthesis is co-controlled by the activity of the chloroplast fructose bisphosphatase.
Full Text
The Full Text of this article is available as a PDF (852.3 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Harris G. C., Cheesbrough J. K., Walker D. A. Effects of mannose on photosynthetic gas exchange in spinach leaf discs. Plant Physiol. 1983 Jan;71(1):108–111. doi: 10.1104/pp.71.1.108. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Heldt H. W., Chon C. J., Maronde D. Role of orthophosphate and other factors in the regulation of starch formation in leaves and isolated chloroplasts. Plant Physiol. 1977 Jun;59(6):1146–1155. doi: 10.1104/pp.59.6.1146. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Laisk A., Sumberg A. Partitioning of the Leaf CO2 Exchange into Components Using CO2 Exchange and Fluorescence Measurements. Plant Physiol. 1994 Oct;106(2):689–695. doi: 10.1104/pp.106.2.689. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sharkey T. D., Berry J. A., Raschke K. Starch and Sucrose Synthesis in Phaseolus vulgaris as Affected by Light, CO(2), and Abscisic Acid. Plant Physiol. 1985 Mar;77(3):617–620. doi: 10.1104/pp.77.3.617. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sharkey T. D. O(2)-insensitive photosynthesis in c(3) plants : its occurrence and a possible explanation. Plant Physiol. 1985 May;78(1):71–75. doi: 10.1104/pp.78.1.71. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sharkey T. D., Stitt M., Heineke D., Gerhardt R., Raschke K., Heldt H. W. Limitation of Photosynthesis by Carbon Metabolism : II. O(2)-Insensitive CO(2) Uptake Results from Limitation Of Triose Phosphate Utilization. Plant Physiol. 1986 Aug;81(4):1123–1129. doi: 10.1104/pp.81.4.1123. [DOI] [PMC free article] [PubMed] [Google Scholar]