Murai M, Yoshida S
Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan.
Plant Cell Physiol. 1998 Jan;39(1):97-105. doi: 10.1093/oxfordjournals.pcp.a029295.
We studied the mechanism of cold acclimation of Jerusalem artichoke (Helianthus tuberosus L.) tubers with special reference to the role of the cell wall. During the cold-acclimation process from September to January, the freezing tolerance of tubers increased from -2.8 degrees C to -8.4 degrees C (LT50). By contrast, the isolated protoplasts constitutively showed a consistent high level of freezing tolerance (LT50; below -25 degrees C) throughout the period. In tuber tissues, freezing injury was effectively protected by the external addition of isotonic solutions. Cryomicroscopic observations revealed that tissue cells mounted in isotonic solutions plasmolyzed upon freezing; tissue cells mounted in water collapsed with a tight attachment of plasma membrane to the cell wall. Upon freezing of intact tissues in water to temperatures below the critical range, the cytoplasm was irreversibly acidified as revealed by a fluorescence pH-ratiometry, suggesting that occurrence of detrimental cellular events leading to permanent cell injury. The freeze-induced acidification of cytoplasm was also effectively prevented by the external addition of isotonic solutions. These results suggest that the tight attachment of the plasma membrane to the cell wall during freezing may have a harmful effect on cells, in particular on the plasma membrane, possibly due to mechanical or some sort of chemical/ physico-chemical interaction with the cell wall.
我们研究了菊芋（Helianthus tuberosus L.）块茎冷驯化的机制，特别关注细胞壁的作用。在9月至1月的冷驯化过程中，块茎的冻融耐受性从-2.8摄氏度提高到-8.4摄氏度（半致死温度）。相比之下，分离的原生质体在此期间始终表现出一致的高冻融耐受性（半致死温度；低于-25摄氏度）。在块茎组织中，通过外部添加等渗溶液可有效保护免受冻融损伤。低温显微镜观察显示，置于等渗溶液中的组织细胞在冷冻时发生质壁分离；置于水中的组织细胞则会塌陷，质膜紧密附着于细胞壁。当完整组织在水中冷冻至低于临界范围的温度时，通过荧光pH比值测定法显示细胞质会发生不可逆酸化，这表明发生了导致永久性细胞损伤的有害细胞事件。通过外部添加等渗溶液也可有效防止冷冻诱导的细胞质酸化。这些结果表明，冷冻过程中质膜与细胞壁的紧密附着可能对细胞，特别是质膜产生有害影响，这可能是由于与细胞壁的机械或某种化学/物理化学相互作用所致。
