PS II down regulation as affected by the maximal activity of photorespiration in leaves of C3 plants

Abstract

The relationship between down regulation of PS II (as indicated by the quenching of chlorophyll fluorescence) and the maximal activity of photorespiration was investigated in leaves of N. tabacum. When leaves were illuminated with low actinic light under different CO2 concentrations in air, the electron flux dependent on photosynthesis (JCO2) increased with increasing the CO2 concentration, and concomitant decrease of the electron flux dependent on photorespiration (JPR) was observed. Under the conditions, however, the rate of total electron flow (Je) was constant within the wide range of CO2 concentrations. On the other hand, when leaves were illuminated with high actinic light, down regulation of PS II was induced even at high CO2 conditions. This phenomenon was analyzed in relation to the maximal activity of photorespiration. We found that the down regulation of PS II is induced when the electron flux (Je) became larger than the flux JPR. On the basis of the results, implication of the PS II down regulation is discussed.