MFI装置を用いたレーザ照射光とレーザ誘起蛍光の葉内分布の測定法に関する研究

Abstract

The chlorophyll fluorescence spectra of green plant leaves induced by a visible laser have strong emission peaks near 685 and 740nm. In order to examine transverse distributions of illuminated laser light and laser-induced chlorophyll fluorescence (687nm: F687 and 741nm: F741) within rice leaves, a micro-fluorescence imaging (MFI) system was devised using a microscope, a CCD camera with an image intensiffer, Ar lasers oscillated with 488and 514.5nm and a He-Ne laser, an image processor, and a microcomputer.Transverse distributions of illuminated laser light and chlorophyll fluorescence in leaves which were projected on the surface of rice leaves with different chlorophyll contents were measured at laserlights with various wavelengths (488, 514.5, and 632.8nm). The distributions of light projected at 541.5 and 632.8nm were observed at a greater depth from the leaf surface than that at 488nm. The attenuation curve of incident laser light in the mesophyll tissue was approximated by an exponential function and it fit well. As a result, the attenuation coefficient α of incident lights of various wavelengths and leaves with different chlorophyll contents could be determined. In order to examine the self-absorption from distributions of the chlorophyll fluorescence in leaves with different chlorophyll contents, profiles of the F741/F687 ratio within mesophyll tissue were measured at various wavelengths. The F741/F687 ratio increased in the case of light with a high absorption coefficient by chlorophyll. We conclude that the MFI system is a useful method to study in order to select the spectral quality of light for plant irradiation.