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首页> 美国卫生研究院文献>Plant Physiology >The Mechanism of Freezing Injury in Xylem of Winter Apple Twigs
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The Mechanism of Freezing Injury in Xylem of Winter Apple Twigs

机译：冬季苹果树枝木质部冻害的机理

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摘要

In acclimated winter twigs of Haralson apple (Pyrus Malus L.), a lag in temperature during cooling at a constant rate was observed at about −41 C by differential thermal analysis. The temperature at which this low temperature exotherm occurred was essentially unaffected by the cooling rate. During thawing there was no lag in temperature (endotherm) near the temperature at which the low temperature exotherm occurred, but upon subsequent refreezing the exotherm reappeared at a somewhat higher temperature when twigs were rewarmed to at least −5 C before refreezing. These observations indicate that a small fraction of water may remain unfrozen to as low as −42 C after freezing of the bulk water in stems. The low temperature exotherm was not present in twigs freeze-dried to a water content below 8.5% (per unit fresh weight), but it reappeared when twigs were rehydrated to 20% water. When freeze-dried twigs were ground to a fine powder prior to rehydration, no exotherm was observed. Previous work has shown that the low temperature exotherm arises from xylem and pith tissues, and that injury to living cells in these tissues invariably occurs only when twigs are cooled below, but not above the temperature of the low temperature exotherm. This study revealed that the low temperature exotherm resulted from the freezing of a water fraction, that the freezing of this water was independent of the freezing of the bulk water, that the exotherm was associated with some gross structural feature but not the viability of the tissue, and that injury to living cells in the xylem and pith was closely and perhaps causally related to the initial freezing of this water.
机译：通过差示热分析，在Haralson苹果（Pyrus Malus L.）的驯化的冬季嫩枝中，在约-41 C的恒定速率下冷却期间观察到温度滞后。发生低温放热的温度基本上不受冷却速率的影响。在解冻期间，在低温放热发生的温度附近没有温度滞后（吸热），但是在随后重新冷冻时，当在重新冷冻之前将树枝重新加热至至少-5℃时，放热以更高的温度再次出现。这些观察结果表明，将茎中的大量水冷冻后，一小部分水可能仍未冷冻至-42C。冷冻干燥至水分含量低于8.5％（每单位鲜重）的树枝中不存在低温放热，但当将树枝重新水合至20％水时会再次出现。在补液前将冻干的树枝磨成细粉时，未观察到放热现象。先前的工作表明，低温放热是由木质部和髓组织产生的，并且仅当将树枝冷却至低温放热的温度以下但不高于低温放热的温度时，这些组织中的活细胞才会不可避免地受到伤害。这项研究表明，低温放热是由水部分的冻结引起的，该水的冻结与大量水的冻结无关，放热与某些总体结构特征有关，但与组织的生存能力无关。 ，木质部和髓中活细胞的伤害与这种水的最初冻结密切相关，也许是因果关系。

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