Department of Horticultural Science, University of Minnesota, St. Paul, Minnesota 55108.
Plant Physiol. 1991 Sep;97(1):182-7. doi: 10.1104/pp.97.1.182.
Freezing, dehydration, and supercooling cause microtubules in mesophyll cells of spinach (Spinacia oleracea L. cv Bloomsdale) to depolymerize (ME Bartolo, JV Carter, Plant Physiol [1991] 97: 175-181). The objective of this study was to determine whether the LT(50) (lethal temperature: the freezing temperature at which 50% of the tissue is killed) of spinach leaf tissue can be changed by diminishing the extent of microtubule depolymerization in response to freezing. Also examined was how tolerance to the components of extracellular freezing, low temperature and dehydration, is affected by microtubule stabilization. Leaf sections of nonacclimated and cold-acclimated spinach were treated with 20 micromolar taxol, a microtubule-stabilizing compound, prior to freezing, supercooling, or dehydration. Taxol stabilized microtubules against depolymerization in cells subjected to these stresses. When pretreated with taxol both nonacclimated and cold-acclimated cells exhibited increased injury during freezing and dehydration. In contrast, supercooling did not injure cells with taxol-stabilized microtubules. Electrolyte leakage, visual appearance of the cells, or a microtubule repolymerization assay were used to assess injury. As leaves were cold-acclimated beyond the normal period of 2 weeks taxol had less of an effect on cell survival during freezing. In leaves acclimated for up to 2 weeks, stabilizing microtubules with taxol resulted in death at a higher freezing temperature. At certain stages of cold acclimation, it appears that if microtubule depolymerization does not occur during a freeze-thaw cycle the plant cell will be killed at a higher temperature than if microtubule depolymerization proceeds normally. An alternative explanation of these results is that taxol may generate abnormal microtubules, and connections between microtubules and the plasma membrane, such that normal cellular responses to freeze-induced dehydration and subsequent rehydration are blocked, with resultant enhanced freezing injury.
冷冻、脱水和过冷会导致菠菜（Spinacia oleracea L. cv Bloomsdale）叶肉细胞中的微管解聚（ME Bartolo，JV Carter，植物生理学[1991]97：175-181）。本研究的目的是确定通过减少微管解聚的程度来改变菠菜叶片组织的 LT（50）（致死温度：组织有 50%死亡的冷冻温度）是否可以改变。还研究了微管稳定如何影响细胞外冷冻、低温和脱水成分的耐受性。在冷冻、过冷或脱水之前，用 20 微摩尔紫杉醇（一种微管稳定化合物）处理非驯化和冷驯化的菠菜叶段。紫杉醇稳定微管，防止细胞受到这些应激时的解聚。紫杉醇预处理后，非驯化和冷驯化细胞在冷冻和脱水过程中表现出更高的损伤。相比之下，用紫杉醇稳定微管不会伤害过冷的细胞。电解质泄漏、细胞的视觉外观或微管重聚合测定用于评估损伤。随着叶片在正常的 2 周驯化期之外进一步驯化，紫杉醇对冷冻过程中细胞存活的影响较小。在驯化长达 2 周的叶片中，用紫杉醇稳定微管会导致在更高的冷冻温度下细胞死亡。在冷驯化的某些阶段，如果在冻融循环中不发生微管解聚，植物细胞将在比微管解聚正常进行时更高的温度下死亡。对这些结果的另一种解释是，紫杉醇可能会产生异常的微管，以及微管与质膜之间的连接，使得细胞对冷冻诱导的脱水和随后的再水化的正常反应被阻断，导致增强的冷冻损伤。
