Changes in the photosynthetic performance, the activity of enzymes of nitrogen metabolism, and proline content in the leaves of wheat plants after exposure to low CO2 concentration

The changes in photosynthetic activity, as well as the activity of nitrogen-metabolism enzymes, the intensity of lipid peroxidation, and proline content were studied in Triticum aestivum L. plants after their incubation at a low CO2 concentration in a sealed chamber for 10 d. CO2 deficiency (-CO2) compared to normal CO2 concentration (control) led to a decrease in the rate of O-2 gas exchange at the plateau of the light curve and quantum yield of photosynthesis. The maximum and effective quantum photochemical yields also decreased. CO2 deficiency reduced the activity of nitrate reductase, but increased the activities of nitrite reductase, glutamine synthetase, and glutamate dehydrogenase, and promoted proline accumulation. It is assumed that with a lack of CO2, an excess of nitrogen-containing compounds occurs, which must be removed from metabolic processes. Also, we suggest the partial storage of nitrogen in the form of nitrogen-containing compounds such as proline.