Fluorescence of chlorophyll in photosynthetic systems II. Induction of fluorescence in isolated spinach chloroplasts

Isolated spinach chloroplasts show a simpler time course of chlorophyll fluorescence in the induction period than that reported previously with living cells. The effects on the time course of many factors (addition of photosynthetic inhibitors, Hill oxidants, heat treatment, light intensity, pre-illumination and background light) were investigated. Inhibitors such as 3(4′-chlorophenyl)-1,1-dimethylurea, and o-phenanthroline caused the same remarkable effect on the time course, which was different from that caused by heat treatment of the chloroplasts. The back flow of electrons, which was considered in the analysis of steady-state fluorescence in our previous paper, is also taken into consideration in the present study. A scheme is proposed to account for the findings with respect to the fluorescence during the induction period. The quantity “work integral” is introduced to correlate the observed lowering of fluorescence during the induction period with the utilization of the absorbed light energy. The concentrations of the oxidation-reduction substances in the scheme were estimated from the “work integral” obtained under varied experimental conditions.