Change of Cell Wall Properties in Woody Plant Cells by Low Temperature

本研究探讨了木本植物细胞的冷温适应及其与细胞壁性质的关系。本研究通过低温扫描电子显微镜提供了一个新的证据，表明包括北方阔叶树种在内的所有细胞壁较厚且坚硬的阔叶木树种的木质部薄壁组织细胞都通过深度过冷来响应过冻温度。木质部薄壁细胞深度过冷的机制已经被研究过，并假设是由于细胞壁中的微毛细管尺寸较小所致。然而，这项研究证实，在细胞外冷冻和深过冷之间，细胞壁的毛细血管大小没有明显变化。这一研究提供了一个新的证据，即木质部细胞原生质体中的可溶性物质的提取可以明显降低过冷程度，这表明抗冻物质的积累可能会极大地促进深度过冷。我们目前正在分析候选的抗冻蛋白，并克隆它们的基因。此外，本研究还对木本植物皮层薄壁组织细胞的冷冻适应机制进行了研究，木本植物的皮层薄壁组织细胞壁较薄，通过胞外冷冻来适应亚冰冻温度。所有这些结果揭示了木本植物细胞对环境胁迫的特殊生理反应，并暗示了从木本植物细胞中提取胁迫诱导蛋白的工业化应用的可能性。

This study concerned to cold temperature adaptation of woody plant cells with the relation to the cell wall properties. This study provided a new evidence by cryo-scanning electron microscopy that xylem parenchyma cells of all hardwood species with thick and rigid cell walls, including boreal hardwood species, responded to subfreezing temperatures by deep supercooling. The mechanism of deep supercooling in xylem parenchyma cells has been studied in previous works and hypothesized to be due to the smaller size of micro-capillaries in the cell walls. However, this study confirmed that there was no distinct change in capillary size of the cell walls between cells exhibiting extracellular freezing arid deep supercooling. This study provided a new evidence that degree of supercooling is distinctly reduced by extraction of soluble substances in xylem cell protoplasts, suggesting the accumulation of antifreeze substances, which might drastically promote deep supercooling. We are currently analyzing candidates of antifreeze proteins and cloning their genes. In addition to these studies, this study also concerned to freezing adaptation mechanisms of cortical parenchyma cells of woody plants, which had comparatively thin soft cell walls and adapted to subfreezing temperature by extracellular freezing. All these results revealed specific physiological response of woody plant cells to environmental stresses as well as suggested the possibility of industrial application of stress-induced proteins from woody plant cells.