Jyske Tuula, Fujiwara Takeshi, Kuroda Katsushi, Iki Taiichi, Zhang Chunhua, Jyske Tuomas K, Abe Hisashi
Finnish Forest Research Institute, Vantaa Research Unit, PO Box 18, FI-01301 Vantaa, Finland
Forestry and Forest Products Research Institute, 1 Matsunosato, Tsukuba, Ibaraki 305-8687, Japan.
Tree Physiol. 2014 Aug;34(8):856-68. doi: 10.1093/treephys/tpu008. Epub 2014 Mar 15.
To investigate the biological mechanism by which trees control the changes in microfibril (MF) orientation among secondary cell wall layers of conifer tracheids, we studied seasonal variation in the orientation of newly deposited MFs during tracheid cell wall development in Japanese cedar (Cryptomeria japonica D. Don) trees growing in Central Japan (36°36'N, 140°39'E). Sample blocks were repeatedly collected from four 16-year-old clones of different origins during the growing season of 2010 to investigate the hypotheses that changes in cellulose MF orientation between wall layers exhibited seasonal and clonal differences. The progressive change in the orientation of newly deposited MFs on the primary and secondary cell wall layers of tracheids was detected by field-emission-scanning electron microscopy. Tracheid production and differentiation was studied by light microscopy. We observed a decreasing trend in the orientation of deposited MFs from earlywood to latewood in the S2 and S1 layers, where MFs appeared in a Z-helix. In contrast, no seasonal pattern in the orientation of the MFs in the S-helix was observed. Minor clonal variation was observed in the phenology of tracheid production and differentiation. We concluded that a seasonal decreasing trend in the orientation of the MFs in the Z-helix in S1 and S2 was present, whereas the MFs in other layers exhibited minor random variations. Thus, the orientation of the MFs in S2 was affected by seasonal factors, whereas the MFs in other layers were more intrinsically controlled. The within-ring variations in the MF orientation and thus the resulting average MF angle might also be related to genotypic differences in the tracheid production and differentiation rate. However, our results do not exclude other intrinsic and environmental regulations in the change in MF orientation, which remains a topic for future studies.
为了探究树木控制针叶树管胞次生细胞壁层间微纤丝（MF）取向变化的生物学机制，我们研究了生长在日本中部（北纬36°36′，东经140°39′）的日本柳杉（Cryptomeria japonica D. Don）树管胞细胞壁发育过程中新沉积MF取向的季节变化。在2010年生长季节，从四个不同来源的16年生克隆植株上反复采集样本块，以研究细胞壁层间纤维素MF取向变化呈现季节性和克隆差异的假设。通过场发射扫描电子显微镜检测管胞初生和次生细胞壁层上新沉积MF取向的渐进变化。通过光学显微镜研究管胞的产生和分化。我们观察到，在S2和S1层中，从早材到晚材，沉积MF的取向呈下降趋势，其中MF呈Z螺旋状出现。相比之下，未观察到S螺旋中MF取向的季节性模式。在管胞产生和分化的物候方面观察到微小的克隆变异。我们得出结论，S1和S2中Z螺旋的MF取向存在季节性下降趋势，而其他层中的MF表现出微小的随机变化。因此，S2中MF的取向受季节因素影响，而其他层中的MF受更多内在因素控制。MF取向的年轮内变化以及由此产生的平均MF角度也可能与管胞产生和分化速率的基因型差异有关。然而，我们的结果并不排除MF取向变化中的其他内在和环境调节因素，这仍是未来研究的一个课题。
