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.