On the state 1-state 2 phenomenon in photosynthesis

The State 1-State 2 phenomenon of photosynthesis was studied in Chlorella by measuring the flash yield (Y) and the modulated rate ( v ) of oxygen evolution induced by weak modulated 650-nm light. From light intensity curves, intensities of 650 and 710 nm background and preilluminations were chosen to give maximum values of Y and v . Following long preilluminations in 710 nm (State 1) or in 650 nm (State 2), Y and v were measured in background light of chosen wavelength. The resulting plots of v vs Y show a discontinuity between State 1 and State 2. They confirm the predictions of Bonaventura and Myers [(1969) Biochim. Biophys. Acta 189, 366–383] and are consistent with changes in α (fraction of absorbed light captured by System II) as explanation of the State 1–State 2 phenomenon. When the intensity of 710 nm preillumination was too low, the characteristics of State 1 were not fully developed and the results then were similar to those of Delrieu [(1972) Biochim. Biophys. Acta 256, 293–299].