单叶省藤材胞间层超微结构及多糖组成

The Ultrastructure and Polysaccharides Composition of Middle Lamella in Rattan Cane(Calamus simplicifolius)

【目的】分析我国重要商业藤种——单叶省藤材胞间层超微结构及多糖组成,深入理解藤材细胞壁生物合成规律和力学失效机制,为藤材增韧改性以及高性能藤基复合材料开发提供理论依据。【方法】采用透射电子显微镜(TEM)和共聚焦显微拉曼光谱技术,对酸性亚氯酸钠溶液处理的藤茎横切面切片进行成像研究,分析不同类型细胞间层的微纳结构特征及多糖组成特点。【结果】TEM成像结果显示,单叶省藤材纤维和薄壁细胞分为胞间层(角隅胞间层和复合胞间层)、初生壁和次生壁,且次生壁具有宽窄交替的同心层状结构。部分脱除木质素后,纤维细胞间的角隅胞间层暴露出纤丝状网络结构,复合胞间层与邻近次生壁剥离,而薄壁细胞间层区域发生明显润胀和形变。高空间分辨率共聚焦显微拉曼光谱能够揭示出藤材纤维细胞和薄壁细胞不同形态区域中木质素、纤维素、木聚糖和果胶类物质分布规律,碳水化合物及木质素C—H伸缩振动(2789~3000 cm^(-1))特征峰成像可有效区分纤维和薄壁细胞各形态区域。木质素芳香环伸缩振动特征峰(1598 cm^(-1))积分成像发现,薄壁细胞间层木质素最易脱除,纤维细胞间层次之,2类细胞次生壁因存在酯键和醚键相连的木质素碳水化合物复合体,木质素脱除量最小。纤维素(380 cm^(-1))、木聚糖(1318 cm^(-1))和果胶(854 cm^(-1))特征峰积分成像发现,2类细胞次生壁纤维素和木聚糖呈现均一分布规律,而果胶类物质广泛存在于胞间层区域,尤其是薄壁细胞间层中。【结论】整合TEM与共聚焦显微拉曼光谱成像技术,能够成功揭示出藤材纤维和薄壁细胞间层的超微结构特征及多糖组成特点。部分脱除木质素后,纤维细胞间的角隅胞间层呈现交联的纤丝状网络结构,而薄壁细胞间层区域发生润胀,细胞间隙增大。拉曼光谱化学成像进一步证实细胞间层区域中富含果胶类物质和少量木聚糖,而纤维素较为均一地分布于细胞次生壁中。

【Objective】In order to deepen our understanding of the cell wall biosynthesis and mechanical failure of rattan cane(Calamus simplicifolius,an important commercial rattan species in China),cell wall ultrastructure and polysaccharides composition of the middle lamella(cell corner middle lamella,ccml,and compound middle lamella,cml)were investigated,which will provide theoretical instruction for the toughening of rattan cane and manufacture of rattan based composites.【Method】The rattan cane sections delignified by acid sodium chlorite was visualized by TEM(transmission electron microscope)and confocal Raman microscopy in order to reveal the ultrastructure and polysaccharides composition in middle lamella areas.【Result】TEM images revealed that the fiber and parenchyma wall was divided into middle lamella(ccml and cml),primary wall and alternating broad and narrow layered secondary wall.After partial delignification,fibrillar structures at the ccml of fiber were observed,while the cml was detached from the adjacent secondary wall.The cml area of parenchyma was swelling and distorted.High spatial resolution confocal Raman microscopy was used to visualize the lignin,cellulose,xylan and pectin distribution.The secondary wall and middle lamella of fiber and parenchyma was easily differentiated by integrating over the band regions from 2789-3000 cm^(-1)(C—H stretching).By integrating over the lignin band at 1598 cm^(-1),it was found that the lignin located at middle lamella areas between fiber and parenchyma was more difficult to be removed relative to that between fibers,while there existed large number of lignin within the secondary wall,probably due to the linkage between lignin and polysaccharides by ether and ester bonds.By integrating over the cellulose,xylan and pectin band at 380 cm^(-1),1318 cm^(-1) and 854 cm^(-1),it was found that cellulose and xylan were uniformly distributed within the fiber and parenchyma secondary wall,while pectin mainly accumulated within the middle lamella areas,especially the cml between parenchyma.【Conclusion】The ultrastructure and polysaccharides composition of the middle lamella in rattan cane was investigated by combining in TEM and confocal Raman microscopy.Entangled fibrillar structure was visualized in the delignified ccml of fiber,while parenchyma displayed swelling cml and enlarged gap between adjacent cells.Furthermore,Raman images revealed that there was abundant pectin and small amounts of xylan in the middle lamella,while cellulose homogeneously deposited within in the secondary wall.