Picosecond time-gated microscopy of UV-damaged plant tissue.

We demonstrate that picosecond time-gated fluorescence microscopy can be used to monitor subtle changes in the kinetics and spatial distribution of perturbations to the molecular and cellular structure of plant tissue caused by ultraviolet radiation. Single-molecule experiments on Photosystem II and chloroplast preparations give picosecond fluorescence decay kinetics that are similar to those obtained previously on bulk samples. For green plant leaves, localized and well-defined cellular structure is seen for normal material whereas relatively diffuse and non-specific features are seen after UV-irradiation indicating significant UV-induced rupture of the cellular structure. The changes in the chlorophyll fluorescence decay kinetics indicate uncoupling of chlorophyll molecules in the light-harvesting system leading to inhibition of energy reorganization and transfer in the antennae and subsequent exciton transfer to the reaction centers.