Comparison of the induction method with the saturation pulse method in chlorophyll fluorescence imaging

Abstract

The effects of a commercially available urea herbicide (including DCMU) on attached Cucumis sativus L. leaves were analyzed by the saturation pulse and the chlorophyll fluorescence induction (CFI) methods. The fluorescence parameters NPQ and Yield, which represent non-photochemical quenching and photosystem ? photochemical efficiency respectively, were calculated from fluorescence images taken by the saturation pulse method. The chlorophyll fluorescence induction images were obtained by the CFI method. NPQ images were useful to quantify the photosynthetic injuries in sites located near the veins caused by the herbicide. However, Yield images could not detect the injuries, because both maximal (F¿m) and steady-state (F) fluorescence intensities under light conditions used for Yield calculation increased at the same rate. On the other hand, induction images detected inhibition of primary electron transport caused by the herbicide. This information was useful to diagnose that the injuries were mainly caused by DCMU in the herbicide. These injuries were also detected with diffusion porometer measurements as a decrease in stomatal conductance and assimilation rate. As another aspect of the methods, difference in size of the measurement areas was considered. The saturation pulse method, which required an evenly distributed, high-level of photosynthetic active radiation (PAR) (saturation light pulse), was limited to a small leaf area. In contrast, the CFI method did not require high PAR and was easier to use for large leaf areas.