Changes in Rubisco Localization and the Activities of C4 Enzymes in Kochia prostrata Under Elevated CO2 and Temperatures

The content and localization of Rubisco large subunit (RbcL), as well as the activities of NADP-MDH and NADP-ME enzymes involved in the C4 carbon-concentrating mechanism (CCM) were studied under elevated (800 ppm, eCO2) CO2 concentration at optimal (25°C) and elevated (32°C, eT) temperatures in the leaves of C4-NADP species Kochia prostrata. In control plants Rubisco was revealed not only in the bundle sheath cells (BS), typical of C4 plants but also in the mesophyll cells (M), indicating a C4-like type of photosynthesis. In addition, the presence of starch grains in the BS and the adjacent layer of mesophyll cells (M(I)) suggests the Calvin cycle activity. eT and/or eCO2 markedly reduced the number of starch grains in these cells, probably as a result of decreased activity of C4 CCM (NADP-MDH and NADP-ME activities). NADP-MDH activity was sensitive to temperature, while that of NADP-ME decreased under eT or eCO2 but most conspicuously when they acted together. Under eCO2, regardless of temperature, the appearance of starch grains was observed in the cells of the second mesophyll layer (M(II)), which also indicated Calvin cycle activity. Thus, K. prostrata exhibits the signs of C4-like photosynthesis and, possibly, an active C3 cycle in the M(II) cells under eCO2 alone or combined with eT.