Fig. 1.

The 77 K fluorescence spectra of state 1-locked (dash) and state 2-locked (line) C. reinhardtii cells. The λ_exc was 440 nm. Note that the concentrations of the cells were identical for both states, and the same was true for all of the settings of the fluorimeter. Therefore, the intensities of the spectra can be directly compared with each other in an absolute sense. The fluorescence quantum yield of PSI in state 2 is only slightly higher than in state 1.