Photosynthesis and nitrogen metabolism in leaves of wheat at low atmospheric CO2 concentration

The purpose of this research was to study changes in photosynthesis parameters, activity of nitrogen metabolism enzymes and proline content after incubating wheat plants at a low concentration of CO2 in a sealed chamber for 10 days. Decrease of the CO2 concentration in the atmosphere was accompanied by a change in a number of photosynthetic parameters when using CO2 as an electron acceptor in the photosystem I. There was a decrease in the gas exchange rate on the plateau of the light curve, the magnitude of the light compensation point, and the intensity of light when the light curve saturates. On the contrary, when NO2- as an electron acceptor was used, the photosynthetic parameters in the analysis of light curves of the O2 emission varied insignificantly both under natural CO2 concentration conditions and in the case of its deficiency. Consequently, with a CO2 deficit, the significance of NO2- as an acceptor of photosynthetic electrons increased, which could lead to a change in the C/N balance in the direction of enhancing nitrogen metabolism in plant cells. This was also indicated by the increase in the activity of glutamine synthetase, the key enzyme of this pathway. The increase in the activity of nitrogen metabolism enzymes at the deficit of carbon skeletons could lead to an excess of nitrogenous compounds and the need to withdraw them from the sphere of metabolic reactions. As a result, accumulation of proline as a conditionally reserve substance was observed, the limiting concentration of which, however, depended on the proline dehydrogenase activity.