Imaging of the blue, green, and red fluorescence emission of plants: An overview

An overview is given on the fluorescence imaging of plants. Emphasis is lai d upon multispectral fluorescence imaging in the maxima of the fluorescence emission bands of leaves, i.e., in the blue (440 nm), green (520 nm), red (690 nm), and far-red (740 nm) spectral regions. Details on the origin of t hese four fluorescence bands are presented including emitting substances an d emitting sites within a leaf tissue. Blue-green fluorescence derives from ferulic acids covalently bound to cell wails, and the red and far-red fluo rescence comes from chlorophyll (Chi) a in the chloroplasts of green mesoph yll cells. The fluorescence intensities are influenced (1) by changes in th e concentration of the emitting substances, (2) by the internal optics of l eaves determining the penetration of excitation radiation and partial re-ab sorption of the emitted fluorescence, and (3) by the energy distribution be tween photosynthesis, heat production, and emission of Chi fluorescence. Th e set-up of the Karlsruhe multispectral fluorescence imaging system (FIS) i s described from excitation with UV-pulses to the detection with an intensi fied CCD-camera. The possibilities of image processing (e.g., formation of fluorescence ratio images) are presented, and the ways of extraction of phy siological and stress information from the ratio images are outlined. Examp les for the interpretation of fluorescence images are given by demonstratin g the information available for the detection of different developmental st ages of plant material, of strain and stress of plants, and of herbicide tr eatment. This novel technique can be applied for near-distance screening or remote sensing.