Chlorophyll Fluorescence Imaging at 77 K for Assessing the Heterogeneously Distributed Light Stress Over a Leaf Surface

Abstract

We developed a chlorophyll fluorescence imaging system that is capable of capturing chlorophyll fluorescence intensity images (F683 and F730) of plant leaves at liquid nitrogen temperature (77 K). F683 is mainly emitted from photosystem (PS) II and light harvesting complex (LHC) II and F730 is mainly emitted from PS I and LHC I, therefore the ratio image of F730 to F683 (i.e. F730/F683) indicates the relative changes in the status of the light energy utilization in the photosystems, e.g. state transition, and can be used to produce maps of relative levels of light stress over a leaf's surface. Using this system, we assessed the heterogeneously distributed light stresses over kidney bean leaf surfaces, caused by light irradiance and representative photosynthesis inhibitor (DCMU and DTT) infiltration treatments. As a result, F730/F683 increased in the light-irradiated leaf areas but remained at a lower value in the DCMU- and DTT-infiltrated leaf areas. These results prove that this 77 K chlorophyll fluorescence imaging system is capable of assessing the light stress that is heterogeneously distributed over a leaf surface.