Department of Agronomy, Cornell University, Ithaca, New York 14853.
Plant Physiol. 1978 Nov;62(5):699-705. doi: 10.1104/pp.62.5.699.
Possibilities to account for the mechanism of freeze-thaw injury to isolated protoplasts of Spinacia oleracea L. cv. Winter Bloomsdale were investigated. A freeze-thaw cycle to -3.9 C resulted in 80% lysis of the protoplasts. At -3.9 C, protoplasts are exposed to the equivalent of a 2.1 osmolal solution. Isolated protoplasts behave as ideal osmometers in the range of concentrations tested (0.35 to 2.75 osmolal), arguing against a minimum critical volume as a mechanism of injury. Average protoplast volume after a freeze-thaw cycle was not greatly different than the volume before freezing, arguing against an irreversible influx of solutes while frozen. A wide variety of sugars and sugar alcohols, none of which was freely permeant, were capable of protecting against injury which occurred when protoplasts were frozen in salt solutions. The extent of injury was also dependent upon the type of monovalent ions present, with Li = Na > K = Rb = Cs and Cl >/= Br > I, in order of decreasing protoplast survival. Osmotic conditions encountered during a freeze-thaw cycle were established at room temperature by exposing protoplasts to high salt concentrations and then diluting the osmoticum. Injury occurred only after dilution of the osmoticum and was correlated with the expansion of the plasma membrane. Injury observed in frozen-thawed protoplasts was correlated with the increase in surface area the plasma membrane should have undergone during thawing, supporting the contention that contraction of the plasma membrane during freezing and its expansion during thawing are two interacting lesions which cause protoplast lysis during a freezethaw cycle.
研究了造成菠菜游离原生质体冻融损伤的机制。-3.9°C 的冻融循环会导致 80%的原生质体破裂。在-3.9°C 下，原生质体暴露于相当于 2.1 毫渗摩尔溶液的环境中。在测试的浓度范围内（0.35 至 2.75 毫渗摩尔），游离原生质体表现为理想的渗透压计，这否定了最小临界体积作为损伤机制的假说。与冷冻前相比，冷冻-解冻循环后原生质体的平均体积没有太大差异，这表明冷冻过程中溶质没有不可逆转地流入。多种糖和糖醇都不能自由渗透，但都能够保护原生质体免受盐溶液冷冻造成的损伤。损伤的程度也取决于存在的单价离子的类型，Li = Na > K = Rb = Cs 和 Cl >/= Br > I，按原生质体存活率降低的顺序排列。通过将原生质体暴露于高盐浓度然后稀释渗透压，在室温下建立了冻融循环中遇到的渗透条件。只有在稀释渗透压后才会发生损伤，并且与质膜的膨胀相关。在冷冻-解冻的原生质体中观察到的损伤与质膜在解冻过程中应该经历的表面积增加有关，这支持了这样的论点，即在冷冻过程中质膜的收缩及其在解冻过程中的扩展是导致原生质体在冻融循环中破裂的两个相互作用的损伤。
