AN ANALYSIS OF THE CHLOROPHYLL-FLUORESCENCE TRANSIENTS FROM PEA LEAVES GENERATED BY CHANGES IN ATMOSPHERIC CONCENTRATIONS OF CO-2 AND O-2

Removal of CO2 from pea leaves, which were either grown in a glasshouse at 15.degree. C or in a controlled environment at 23.degree. C, produced an initial increase in chlorophyll fluorescence emission followed by a slow decrease to steady state. From estimations of the redox state of Q, using a nondestructive in vivo technique, the contributions of photochemical and nonphotochemical quenching processes to these fluorescence transients were determined. The fluorescence changes observed on removal of CO2 from the 2 types of pea leaves were mainly attributable to changes in nonphotochemical quenching although markedly different changes in photochemical quenching were also observed. When leaves grown at 23.degree. C were depleted of CO2, Q immediately became more reduced, whereas in leaves grown at 15.degree. C Q, unexpectedly, became more oxidized. On return of CO2 to the leaves these phenomena were reversed, i.e., in leaves grown at 23.degree. C Q became more oxidized and in the 15.degree. C grown leaves Q became more reduced. Increased electron transport to O2 may account for the oxidation of Q on depletion of CO2 from 15.degree. C grown leaves. The generation of fluorescence transients on removal and return of CO2 to the leaf required the presence of O2. The fast fluorescence kinetics observed on exposure of the leaf at steady state to a 2nd saturating irradiation suggest that O2 may accept electrons directly from Photosystem II at a site between Q and B.