Chilling-induced reduction of photosynthesis is mitigated by exposure to elevated CO2 concentrations

This work aimed to evaluate if chilling stress may be mitigated by elevated CO2 (EC) in Beta vulgaris L. plants. Photosynthetic rate was measured at 21% and 2% O-2 after a short-term exposure of 5 h at four different treatments: 360 mu mol(CO2) mol(-1)/25A degrees C (AC); 360 mu mol(CO2) mol(-1)/4A degrees C (AC+LT); 700 mu mol(CO2) mol(-1)/25A degrees C (EC); 700 mu mol(CO2) mol-1/4A degrees C (EC+LT). Compared to AC+LT, EC+LT plants showed higher values of CO2 fixation, photochemical activity, and Rubisco amount. These latter invest a higher portion of photosynthetic electron flow to O-2, differently from AC+LT plants that promote the regulated thermal dissipation processes. In EC+LT plants, the photosynthetic electron flow to O-2 acts as a safety mechanism against the excess of absorbed light, upon return to prechilling conditions, allowing photosynthetic apparatus to maintain its efficiency. In AC+LT plants, the increase of thermal dissipation processes was not adequate to guarantee the PSII photoprotection and the photosynthetic recovery after chilling.