Relationship between cell wall structure and freezing behavior of woody cells.

目前的研究阐明了细胞壁性质在木质部射线薄壁细胞对零度以下温度的适应中的重要作用。首先，我们通过低温扫描电子显微镜观察软木种木质部射线薄壁细胞的冻结行为，发现细胞壁的宏观结构差异对冻结行为有明显的影响。结果表明，由非木质化薄细胞壁构成的木质射线薄壁细胞（Scidopitysverticillata，Pinusdensiflora，P.parifilora）对冻结的反应是细胞外冻结，而由木质化厚细胞壁构成的木质射线薄壁细胞（Cryptomeriajaporiica，Larixleptolepis）对冻结的反应是深度过冷。其次，我们发现，在细胞壁的微观结构差异，这是没有检测到的电子显微镜，也影响到冻结行为的木质部射线薄壁细胞的厚细胞壁与刚性外观。例如，桦树的木质部射线薄壁组织细胞在夏季通过过冷来响应冻结，但在冬季通过细胞外冻结来响应冻结，尽管通过电子显微镜观察没有检测到细胞壁结构的季节性变化。为了阐明细胞壁性质在冷冻行为上的季节性变化的机制，我们检测了细胞壁结合蛋白的季节性变化，并发现低温诱导的质外体蛋白LIAP 29、28和23的明显积累。我们目前正在继续对这些蛋白质进行生物化学分析。

Present research clarified important role of cell wall properties in the adaptation of xylem ray parenchyma cells to subzero temperatures. First, we showed that macroscopic structural differences in the cell walls affected distinctly to the freezing behavior by examing freezing behavior of xylem ray parenchyma cells of softwood species with observation by cryo-scanning electron microscopy. It was shown that xylem ray parenchyma cells constructed of unlignified thin cell walls with soft appearance (Sciadopitys verticillata, Pinus densiflora, P.parifilora) responded to freezing by extracellular freezing, while xylem ray parenchyma cells constructed of lignified thick cell walls with rigid appearance (Cryptomeria japoriica, Larix leptolepis) responded to freezing by deep supercooling. Second, we showed that microscpic structural differences in the cell walls, which were not detected by observation with electron microscopy, also affected to the freezing behavior in xylem ray parenchyma cells constructed of thick cell walls with rigid appearance. For example, xylem ray parenchyma cells of birch responded to freezing by supercooling in summer but they responded to freezing by extracellular freezing in winter, although no seasonal alteration of cell wall structures was detected by electron microscope observations. For clarifying the mechanisms of seasonal alteration of cell wall properties upon freezing behavior, we examined seasonal change of the cell wall-binding proteins and found distinct accumulation of Lowtemperature-Induced Apoplastic Proteins LIAP29, 28 and 23. We are currently continuing the biochemical analysis of these proteins.