COLD HARDINESS AND DEEP SUPERCOOLING IN XYLEM OF SHAGBARK HICKORY
COLD HARDINESS AND DEEP SUPERCOOLING IN XYLEM OF SHAGBARK HICKORY
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DOI：
10.1104/pp.59.2.319
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发表时间：
1977-01-01
期刊：
影响因子：
7.4
通讯作者：
BURKE, MJ
中科院分区：
文献类型：
--
作者：
GEORGE, MF;BURKE, MJ
利用差热分析、差示扫描量热仪、脉冲核磁共振光谱和低温显微镜研究了在-40℃附近发生的低温冰点或放热。在冷驯化的山核桃(Carya ovata L.)使用这些方法的实验表明，低温放热是由细胞水的冻结引起的，这种方式预测了过冷的稀水溶液。山核桃树枝的冷冻放热、核磁共振松弛时间和冻结和解冻曲线都表明，木质部在低于冰点的温度下存在过冷部分。量热和低温显微分析表明，冻结发生在木质部射线薄壁组织的细胞内。过冷度非常稳定，即使在略高于水的均匀成核温度(-38度)的温度下也是如此。c)。木质部水在相对湿度为80%、温度为20度时耐脱水。D2O交换实验发现，山核桃的木质部射线中只存在一个微弱的水分运输动力学障碍。
Differential thermal analysis, differential scanning calorimetry, pulsed NMR spectroscopy and low temperature microscopy are utilized to investigate low temperature freezing points or exotherms which occur near -40.degree. C in the xylem of cold-acclimated shagbark hickory (Carya ovata L.). Experiments using these methods demonstrate that the low temperature exotherm results from the freezing of cellular water in a manner predicted for supercooled dilute aqueous solutions. Heat release on freezing, NMR relaxation times and freezing and thawing curves for hickory twigs all point to a supercooled fraction in the xylem at subfreezing temperatures. Calorimetric and low temperature microscopic analyses indicate that freezing occurs intracellularly in the xylem ray parenchyma. The supercooled fraction is extremely stable, even at temperatures only slightly above the homogeneous nucleation temperature for water (-38.degree. C). Xylem water is resistant to dehydration when exposed to 80% relative humidity at 20.degree. C. D2O exchange experiments find that only a weak kinetic barrier to water transport exists in the xylem rays of shagbark hickory.