The efficiency of the CO 2-concentrating mechanism during single-cell C 4 photosynthesis

Abstract

The photosynthetic efficiency of the CO 2-concentrating mechanism in two forms of single-cell C 4 photosynthesis in the family Chenopodiaceae was characterized. The Bienertioid-type single-cell C 4 uses peripheral and central cytoplasmic compartments (Bienertia sinuspersici), while the Borszczowioid single-cell C 4 uses distal and proximal compartments of the cell (Suaeda aralocaspica). C 4 photosynthesis within a single-cell raises questions about the efficiency of this type of CO 2-concentrating mechanism compared with the Kranz-type. We used measurements of leaf CO 2 isotope exchange (Δ 13C) to compare the efficiency of the single-cell and Kranz-type forms of C 4 photosynthesis under various temperature and light conditions. Comparisons were made between the single-cell C 4 and a sister Kranz form, S.eltonica[NAD malic enzyme (NAD ME) type], and with Flaveria bidentis[NADP malic enzyme (NADP-ME) type with Kranz Atriplicoid anatomy]. There were similar levels of Δ 13C discrimination and CO 2 leakiness (φ{symbol}) in the single-cell species compared with the Kranz-type. Increasing leaf temperature (25 to 30°C) and light intensity caused a decrease in Δ 13C and φ{symbol} across all C 4 types. Notably, B.sinuspersici had higher Δ 13C and φ{symbol} than S.aralocaspica under lower light. These results demonstrate that rates of photosynthesis and efficiency of the CO 2-concentrating mechanisms in single-cell C 4 plants are similar to those in Kranz-type. The photosynthetic efficiency of the CO2 concentrating mechanism in two forms of single-cell C4 photosynthesis in the family Chenopodiaceae was characterized. The Bienertioid type single-cell C4 uses peripheral and central cytoplasmic compartments (Bienertia sinuspersici), while the Borszczowioid single-cell C4 uses distal and proximal compartments of the cell (Suaeda aralocaspica). We used measurements of leaf CO2 isotope exchange (Δ13C) to compare the efficiency of the single-cell and Kranz-type forms of C4 photosynthesis under various temperature and light conditions. There were similar levels of Δ13C discrimination and CO2 leakiness (φ{symbol}) in the single-cell species compared to the Kranz-type. These results demonstrate that rates of photosynthesis and efficiency of the CO2-concentrating mechanisms in single-cell C4 plants are similar to those in Kranz-type. © 2011 Blackwell Publishing Ltd.