Possible Activation of С3 Photosynthesis in С4 Halophyte Kochia prostrata Exposed to an Elevated Concentration of СО2

The effect of an elevated concentration of СО2 (800 ppm) on the growth rate, efficiency of photosystem I (PS I) and photosystem II (PS II), content of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPc), as well as proline and sodium and potassium ions, was investigated in the shoots of С4-halophyte Kochia prostrata (L.) Schrad. An elevated concentration of СО2 caused a decrease in accumulation of dry biomass (1.2 times), a rise in the content of proline (1.2 times) and potassium ions (1.3 times), and a shortening of time required to reach the maximum P700 oxidation level (PS I) (1.7 times). The content of sodium ions and water in the shoots and efficiency of PS II (Fv/Fm) did not change. Immunoblotting showed that, at the elevated concentration of СО2, the ratio between Rubisco and PEPc proteins rose from 1.3 to 3.4. The shortening of time required to reach the maximum oxidation level of PS I indirectly points to a reduction in the activity of cyclic transport of electrons responsible for efficient operation of the С4-carbon-concentrating mechanism. The high concentration of СО2 is suggested to activate the С3-pathway of photosynthesis in С4-halophyte K. prostrata.