通过改良超薄切片制样法观察汉代饱水考古木材细胞壁的超微构造

Optimized sample preparation method for ultrathin sectioning to observed cell wall ultrastructure of water-logged archaeological wood in the Han Dynasty

本研究以汉代饱水考古木材为试材,通过改良超薄切片制样方法,在电镜下观察其细胞壁超微构造,结果表明:(1)取样时垂直于管胞的方向不大于1 mm;微波和真空处理可将每步渗透时间缩短至2~3 h;环氧树脂Spurr与LR White丙烯酸包埋剂相比,与考古木材组织匹配度更佳;1%高锰酸钾处理切片可着染组织中的木质素、增强样本的衬度,但细胞壁层结构清晰度降低;(2)本试样中早材比晚材腐朽严重,管胞次生壁发生通道状降解、偶见凹槽状降解,而射线细胞内无明显腐蚀菌分布,胞间层较完整,次生壁S层较S层更耐腐蚀,推测腐蚀菌可能经由管胞空腔入侵,类似软腐。本研究为后续不同地质年代、不同降解程度的考古木材细胞壁超微结构的研究提供了可靠方法及科学参考。

Water-logged wooden relics are precious archaeological resources. It is very important to investigate the ultrastructural characteristics of the cell wall and analyze its degradation mechanism for the innovation of the conservation methods of water-logged archaeological wooden relics. In this study, water-logged archaeological wood in the Han Dynasty was used for optimizing the ultrathin sectioning processing method and observation of cell wall ultrastructure. The results showed that: 1. The sample thickness vertical to the orientation of the tracheids should be less than 1 mm;microwave and vacuum treatment could shorten the resin infusion time to 2-3 hours per step;and the Spurr’s epoxy resin was better than LR White acrylic acid embedding agent;1% potassium permanganate could stain the lignin in the tissue and enhance the contrast of the sample, but the clarity of the cell wall layers was lower. 2. The decay of the earlywood was more serious than that of the latewood. The secondary cell wall of the tracheids had channel-like degradation and less groove-like degradation, but there were no corrosive bacteria in the ray cells. The integrity of middle lamella was good and the secondary wall layer Swas more corrosion-resistant than layer S. It is suggested that the corrosive bacteria may invade from the lumen and though the layer S, similar to soft rot. This study provides a reliable method for the future study on the ultrastructure of archaeological wood with different geological ages and different degradation degree.