SOFTWOOD AND HARDWOOD LIGNIN FLUORESCENCE SPECTRA OF WOOD CELL WALLS IN DIFFERENT MOUNTING MEDIA
SOFTWOOD AND HARDWOOD LIGNIN FLUORESCENCE SPECTRA OF WOOD CELL WALLS IN DIFFERENT MOUNTING MEDIA
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DOI：
10.1163/22941932-00000002
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发表时间：
2013-01-01
期刊：
影响因子：
1.9
通讯作者：
Donaldson, Lloyd
中科院分区：
文献类型：
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作者：
Donaldson, Lloyd
木材细胞壁由于木质素的存在而天然地具有荧光。自发荧光提供了一种比染色更特异的定位木质素的方法，并且可以潜在地用于评估由一系列生物、化学和物理处理引起的细胞壁修饰。为了优化条件成像木质素的自发荧光，并评估可能的差异，软木和硬木木质素之间的荧光，辐射松和白杨的木材切片进行了检查，通过共聚焦激光扫描显微镜测量荧光光谱的范围内安装介质。甘油/缓冲液混合物在三个不同的pH值进行了比较，浸泡油和硫代二乙醇，使用UV和可见光激发。在可见光激发下，pH 9的甘油/缓冲液产生最强的木质素荧光，表明这是用于成像和光谱学的最佳封固介质。对于UV激发，硫代二乙醇相对于甘油给出增加的亮度。白杨木质素在pH 9的488 nm激发下比松树木质素亮4倍，并且在这些条件下显示出光谱发射的特征差异。这种特征性的荧光被定位到纤维的内部次级壁，表示为从外部S-2区域朝向管腔增加的梯度，如通过光谱解混所可视化的。与其他阔叶树种边材的比较表明，这种荧光发射是白杨和杨柳（杨柳科）的特征。已知杨柳科的成员含有特征性的对羟基苯甲酸异辛酯木质素，并且这种特殊的木质素类型可能是导致白杨纤维壁的特征性pH依赖性荧光的原因。
Wood cell walls are naturally fluorescent due to the presence of lignin. Autofluorescence offers a more specific method for localising lignin than staining and can potentially be used to assess cell wall modification resulting from a range of biological, chemical and physical treatments. In order to optimise conditions for imaging lignin by autofluorescence and to evaluate possible differences in fluorescence between softwood and hardwood lignin, wood sections of radiata pine and poplar were examined by confocal laser scanning microscopy to measure fluorescence spectra in a range of mounting media. Glycerol/buffer mixtures at three different pH values were compared with immersion oil and thiodiethanol using both UV and visible excitation. Glycerol/buffer at pH9 produced the strongest lignin fluorescence at visible excitation indicating that this is the optimal mounting medium for imaging and spectroscopy. For UV excitation, thiodiethanol gave increased brightness relative to glycerol. Poplar lignin was four times brighter than pine lignin with excitation at 488 nm at pH9, and showed characteristic differences in spectral emission under these conditions. This characteristic fluorescence was localised to the inner secondary wall of fibres, expressed as a gradient from the outer S-2 region increasing towards the lumen, as visualised by spectral unmixing. Comparison with sap-wood from other hardwood species suggests that this fluorescence emission is characteristic of poplar and willow (Salicaceae). Members of the Salicaceae family are known to contain characteristic syringyl p-hydroxybenzoate lignin and it is likely that this special lignin type is responsible for the characteristic pH dependant fluorescence of poplar fibre walls.