Chlorophyll Fluorescence Measurements

We measured the chlorophyll fluorescence by using a CF Imager (Technologica, Essex, United Kingdom) and operated it as described by Xiao et al. (2012). In briefly, the leaves were first dark adapted for 10 min before each measurement and the minimum fluorescence yield (F_o) was measured with a measuring light intensity of 0.8 mmol m^-2 s^-1. For measuring the maximum fluorescence yield (F_m), we applied a saturating pulse of white light to the plants for 1 s, and the light intensity is 3000 mmol m^-2 s^-1. We calculated the maximal photochemical efficiency of PSII by the ratio of F_v (F_m – F_o) to F_m. In image analysis, the corresponding data measured in the plants were normalized to a false-color scale with assigned extreme highest value with 0.8 (red) and lowest value with 0.1 (blue), respectively.