モイレ反応と顕微分光測光法によるリグニンの多様性の検討

Abstract

針葉樹材と広葉樹材とを化学的に識別しうるモイレ反応を顕微分光測光法に取り入れることにより, 木材および竹材の細胞壁におけるリグニンの多様性について検討した。針葉樹材1種 (正常材, 圧縮あて材), 広葉樹材3種, およびモウソウチクより, 木口切片を作製し, モイレ処理を行った。そして反応色を観察するとともに顕微分光光度計を用いて測光し, 各種細胞種別間におけるリグニンのタイプの検出を試みた。その結果, グアイアシルリグニンに富む針葉樹材の仮道管と広葉樹材の道管の二次壁においては, モイレ処理によって黄褐色を示し, その紫外 - 可視域吸収スペクトルにおいて280 - 300nm付近の吸収以外に特定の吸収極大が認められなかった。一方, シリンギルリグニンに富む広葉樹材の木部繊維二次壁は赤みを帯びた色を示し, 短波長側の吸収に加えて510 - 520nm付近に吸収が認められた。また各種細胞種 (孔圏道管, 周囲仮道管, 晩材小径道管, 繊維状仮道管など) ではそれぞれ色調がわずかに異なり, その吸収スペクトルにも少し差がみられた。さらに, p-ヒドロキシフェニルリグニンを有するモウソウチクと針葉樹圧縮あて材においては, これらと異なる特異な呈色 (暗褐色から褐色) がみられ, その吸収スペクトルにおいては300 - 400nmに顕著な吸収が認められた。

In order to investigate the varieties of lignin structure in wood and bamboo cell walls, Mäule color reaction was applied to microscopic spectrophotometry. The specimens studied were HINOKI (Chamaecyparis obtusa), MAKANBA (Betula maximowicziana), BUNA (Fagus crenata), MIZUNARA (Quercus crispula), HINOKI compression wood and bamboo MOUSOUCHIKU (Phyllostachys pubescens). HINOKI and MAKANBA were selected as the typical softwood and hardwood, respectively. BUNA is characteristic of fiber-tracheids while MIZUNARA is possessing various types of tracheids and libriform wood fibers. In addition, HINOKI compression wood and MOUSOUCHIKU contain p-hydroxyphenylpropane unit were studied. With the section of 20㎛ stained by Mäule color reaction, various types of cell walls were studied (Figs. 1-6), while UV-VIS absorption was examined with using 6 and 4㎛ sections after the staining (Figs. 7-10). For 1㎛ sections, however, the staining was not applied for studying in the UV range (Fig. 11, Fig. 12). Fiber walls of MAKANBA and MIZUNARA rich in syringyl lignin moiety were stained red showing clear absorption at 510-520 nm, whereas walls of MAKANBA vessels, MIZUNARA earlywood vessels and HINOKI tracheids rich in guaiacyl lignin moiety were stained yellow brown without showing any clear absorption at 510-520 nm. Absorption in the range 510-520 nm is thus due to the presence of the syringyl propane unit. As a result, richness of the syringyl lignin in the cell walls was found to decrease in the following order ; fiber>fiber-tracheid>tracheid≒vessel The fiber is known to act as a mechanical or physical support while the vessel or earlywood tracheid plays an important role in water conduction. Thus, from a cell evolution viewpoint, overall results suggest that the cell type being rich in syringyl lignin acts as mechanical or physical support rather than water conduction. Cell walls of the compression wood tracheids and some cells of the bamboo were stained dark brown and showed peculiar absorption around 300-400 nm after the staining. Also in the untreated sections, absorption at 280-320 nm were detected in bamboo cells. These results are due perhaps to the presence of p-hydroxyphenyl propane unit and p-coumaric acid in these cell walls.