United States Department of Agriculture, Agricultural Research Service, Orlando, Florida 32803.
Plant Physiol. 1989 Feb;89(2):444-51. doi: 10.1104/pp.89.2.444.
Seasonal variations in freezing tolerance, water content, water and osmotic potential, and levels of soluble sugars of leaves of field-grown Valencia orange (Citrus sinensis) trees were studied to determine the ability of citrus trees to cold acclimate under natural conditions. Controlled environmental studies of young potted citrus trees, spinach (Spinacia pleracea), and petunia (Petunia hybrids) were carried out to study the water relations during cold acclimation under less variable conditions. During the coolest weeks of the winter, leaf water content and osmotic potential of field-grown trees decreased about 20 to 25%, while soluble sugars increased by 100%. At the same time, freezing tolerance increased from lethal temperature for 50% (LT(50)) of -2.8 to -3.8 degrees C. In contrast, citrus leaves cold acclimated at a constant 10 degrees C in growth chambers were freezing tolerant to about -6 degrees C. The calculated freezing induced cellular dehydration at the LT(50) remained relatively constant for field-grown leaves throughout the year, but increased for leaves of plants cold acclimated at 10 degrees C in a controlled environment. Spinach leaves cold acclimated at 5 degrees C tolerated increased cellular dehydration compared to nonacclimated leaves. Cold acclimated petunia leaves increased in freezing tolerance by decreasing osmotic potential, but had no capacity to change cellular dehydration sensitivity. The result suggest that two cold acclimation mechanisms are involved in both citrus and spinach leaves and only one in petunia leaves. The common mechanism in all three species tested was a minor increase in tolerance (about -1 degrees C) resulting from low temperature induced osmotic adjustment, and the second in citrus and spinach was a noncolligative mechanism that increased the cellular resistance to freeze hydration.
本研究旨在探讨田间生长的瓦伦西亚橙（Citrus sinensis）叶片的抗冻性、含水量、水势和渗透势以及可溶性糖水平的季节性变化，以确定柑橘树在自然条件下的冷适应能力。通过对盆栽年轻柑橘树、菠菜（Spinacia pleracea）和矮牵牛（Petunia hybrids）的受控环境研究，研究了冷适应过程中的水分关系。在冬季最寒冷的几周，田间生长的树木叶片含水量和渗透势下降了约 20%至 25%，而可溶性糖增加了 100%。与此同时，抗冻性从致死温度（LT(50)）的-2.8 至-3.8 摄氏度增加。相比之下，在生长室中以恒定的 10 摄氏度进行冷适应的柑橘叶片对约-6 摄氏度具有抗冻性。在整个一年中，计算得出的 LT(50)处的冷冻诱导细胞脱水相对稳定，但在受控环境中以 10 摄氏度冷适应的植物叶片中增加。与未冷适应的叶片相比，在 5 摄氏度下冷适应的菠菜叶片能够耐受更大的细胞脱水。冷适应的矮牵牛叶片通过降低渗透势来提高抗冻性，但没有改变细胞脱水敏感性的能力。结果表明，两种冷适应机制涉及柑橘和菠菜叶片，而仅涉及矮牵牛叶片。在所有三种测试的物种中，共同的机制是低温诱导的渗透调节导致的耐受性略有增加（约-1 摄氏度），而柑橘和菠菜的第二个机制是非凝聚机制，增加了细胞对冷冻水合的抵抗力。
