The efficiency of the CO2-concentrating mechanism during single-cell C4 photosynthesis

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). C4 photosynthesis within a single-cell raises questions about the efficiency of this type of CO2-concentrating mechanism compared with the Kranz-type. We used measurements of leaf CO2 isotope exchange (13C) to compare the efficiency of the single-cell and Kranz-type forms of C4 photosynthesis under various temperature and light conditions. Comparisons were made between the single-cell C4 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 13C discrimination and CO2 leakiness in the single-cell species compared with the Kranz-type. Increasing leaf temperature (25 to 30 degrees C) and light intensity caused a decrease in 13C and across all C4 types. Notably, B. sinuspersici had higher 13C and than S. aralocaspica under lower light. 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.