Visualization of the Distribution of Flavonoids in Larix kaempferi Wood by Fluorescence Microscopy

To investigate the accumulation and localization of heartwood extractives in (cid:9488)(cid:9509)(cid:9526)(cid:9517)(cid:9532)(cid:9444)(cid:9519)(cid:9509)(cid:9513)(cid:9521)(cid:9524)(cid:9514)(cid:9513)(cid:9526)(cid:9517) （Lamb.） larch）, fluorescence microscopic observations were performed after staining with 2−aminoethyl diphenylborinate （2−APB, DPBA）. First, three flavonoids （（2(cid:9494), 3(cid:9494)）−taxifolin, （2(cid:9494), 3(cid:9494)）−dihydrokaempferol, （2(cid:9495)）−naringenin） were isolated from Japanese larch heartwood. These compounds were spotted on membranes, which were subjected to fluorescence microscopic observations before and after staining with DPBA. Fluorescence spectra of the solution of these compounds were also measured. As the results, the fluorescence intensities of the flavonoids were enhanced after DPBA staining, and their intensities and color tones were characteristic for each flavonoid. After DPBA staining, fluorescence behaviors of sapwood sections were unchanged compared with the auto-fluorescence （before the staining）, whereas the heartwood showed similar fluorescence to that of the authentic flavonoids, which was confirmed by the membrane tests. Furthermore, after extraction of Japanese larch heartwood sections by methanol, the fluorescence by DPBA staining was significantly weakened. These results indicated that fluorescence from Japanese larch heartwood sections after DPBA staining was derived predominately from the flavonoids in the sections. Consequently, it was revealed that in Japanese larch wood the distribution of heartwood extractive flavonoids could be visualized by fluorescence microscopy after DPBA staining.