Light-intensity dependence of the in vivo fluorescence lifetime of chlorophyll

Abstract— Phase-fluorometer measurements of the fluorescence lifetime, τ, from chlorophyll in Chlorella, Bishop's 8 and 11 Scenedesmus mutants, sugarbeet leaf and chloroplast fragments demonstrate that: τ is independent of modulation frequency at 27 and 14 mc. in the experimental-wavelength range from 650 to 735 nm (with blue or blue-green excitation); with Chlorelfa and chloroplast fragments τ rises hyperbolically with intensity to τ_max about 2 nsec and 0·7 nsec respectively; DCMU poisoned Chlorella and sugarbeet leaf as well as the mutants have τ values near 2 nsec; the lifetime-incident intensity relationship for Chlorella and chloroplast fragments is quantitatively similar to the incident-intensity dependence of fluorescence yield and oxygen evolution and thus supports the hypothesis that these three measuring variables are controlled by the concentration of ‘open’ trapping systems; τ is independent of emission wave-length to suggest that fluorescence is dominated by a single chlorophyll species. The reaction velocity-lifetime correlation indicates that fluorescence behavior is directly controlled by system II.