【目的】分析光皮桦应拉木的显微结构、理化特性及其形成早期的内源激素分布，以期为揭示应拉木形成机制提供理论依据。【方法】以无性系1V25-2为材料，通过人工拉弯诱导形成应拉木，测定其主要显微特征和物理化学特性，并应用 ELISA分析其形成早期阶段主要内源激素的分布规律。【结果】经12个月的拉弯处理，应拉区木质部的细胞壁明显增厚，纤维平均双壁厚是对应木的1.8倍，形成明显的胶质纤维层。应拉木的平均纤维长度、纤维素含量均明显大于对应木，而木质素含量则相反。拉弯处理的早期阶段，不同木质部类型中的4种激素含量呈现不同的分布特征。应拉区木质部中 IAA含量均小于对应区，但仅处理7天的木质部样品两区块间差异达到显著水平。GAs(GA1+GA3)也表现出与 IAA类似的变化规律。除拉弯处理6 h的样品外，应拉区木质部 BR 含量均显著小于对应区和对照，且随着处理时间延长对应区木质部 BR含量呈递增趋势。ZR含量在应拉区和对应区木质部间皆无明显差异，但表现出随处理时间延长而增加的趋势，处理7天时2区块的 ZR 含量均显著高于对照。【结论】经12个月的拉弯处理，光皮桦应拉区木质部的细胞壁明显增厚，出现明显的胶质纤维层；平均纤维长度、纤维素含量增加，表现出特有的理化特征。在拉弯处理早期阶段，4种内源激素在木质部中的含量呈现出不同的分布变化，推测这些激素的重新分布可能与光皮桦应拉木的形成有一定关系。%Objective]Reaction wood is one of the limiting factors for efficient cultivation and wood utilization of fast-growing timber species. There are various types of tension woods ( TWs) in Betula luminifera plantation,but the research on their characteristics and forming causes is absent. In this study,microscopic structure,physical and chemical characteristics of B. luminifera TW were determined,and distributions of endogenous hormones were analyzed during the early period of its formation to provide knowledge of the TW formation mechanism in birch.[Method]B. luminifera clone 1V25-2 was used for artificially inducing tension wood by bending. Anatomical characteristics of xylems were observed,and fiber characteristics, microfibril angle,and contents of cellulose and lignin were determined. The distributions of four endogenous hormones were analyzed using the ELISA during the early period of TW formation ( from 6 h to 7 d of a tension time course) .[Result]TWber presented a conspicuously thickened inner layer of the cell wall after bending for 12 months,and the fiber of the double wall was averagely 1. 8 times more thickness than the opposite wood (OW) fiber. The double-stained results with Safranin-Astra blue showed that a gelatinous layer deposited in the lumen side of secondary cell wall of TW. Fiber lengths and cellulose contents of TW were both obviously greater than those of OW,but lignin contents exhibited the converse tendency. At the early stages of bending treatment,four endogenous hormones showed the distinct distributions in different xylem regions. The IAA content of TW was all lower than that of OW,but the difference between the two regions reached to significant level only after 7 days bending. The distributions of GAs ( GA1 +GA3 ) were same as IAA. Except for the sample of 6 h bending,the BR contents of OW were significantly higher than those of TW,and showed a rising tendency as bending progressed. Although ZR content showed a rising tendency as bending progressed,their differences between TW and OW were insignificant for each sampling time. However,the ZR content of TW and OW was significantly higher than that of the control after 7-day of bending.[Conclusion]After 12 months bending,cell walls of B. luminifera were obviously thickened in TW xylem. A typical gelatinous layer was deposited in the lumen side of secondary cell wall of this region. And specific physical and chemical characteristics,such as the longer fibers and higher cellulose content,were found in TW. At the early stages of bending,four endogenous hormones showed the different distribution patterns in the xylems,implying that re-distributions of these hormones may be associated with the TW formation in B. luminifera.
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