Maier Maria, Kappen Ludger
Lehrstuhl für Botanik II der Universität Würzburg, Mittlerer Dallenbergweg 64, D-8700, Würzburg, Federal Republic of Germany.
Oecologia. 1979 Jan;38(3):303-316. doi: 10.1007/BF00345190.
Evidence was given that the freezing tolerance of Halimione portulacoides, a wintergreen halophyte, can be explained by protection of sensitive cellular membranes in vivo. Experiments were done with cloned cuttings of a plant from the German North Sea coast. One series received no NaCl (O-plants) the other 3% NaCl (NaCl-plants) in the nutrient solution. During the annual course Na and Cl of the O-plant leaves remained on a nearly constant low level. In the leaves of the NaCl-plants Na and Cl concentrations changed strongly during year and reached a maximum in winter. Potassium was always on a low level. The freezing tolerance curves showed a minimum in summer and a maximum in winter. The small difference between the freezing tolerance peaks of the NaCl- and O-plants indicated that the increased salt stress did not affect freezing tolerance very much. Freezing stress in cellular membranes, like thylacoids, acts in the same way as increasing salt concentration; consequently both together must amplify the stress. For the analysis of their ion contents chloroplasts of H. portulacoides were non-aqueously isolated from leaves with different freezing tolerance during the year. In midwinter, when freezing tolerance was highest, the chloroplasts of the NaCl-plants contained about 250 mM chloride (O-plants c. 150 mM), while the non-plastidic fraction of the cell contained about 1 M (O-plants c. 400 mM) chloride. On the other hand citrate reached high concentrations in the chloroplasts in winter. Non-volatile organic acids like citrate are known to compensate colligatively the injurious action of the inorganic salt ions on thylacoids in vitro (Heber and Santarius, 1976). The molar proportion between chloride and citrate in H. portulacoides chloroplasts decreased with increasing freezing tolerance and reached values which were protective on chloroplast membranes in vitro. This relationship in vivo with H. portulacoides provides evidence supplying the concept of colligative protection of cellular membranes. Besides citrate also malate may act as a colligatively protecting agent against the amplified salt stress by freezing.
有证据表明，冬青盐生植物海滨碱蓬的耐冻性可以通过体内敏感细胞膜的保护来解释。实验使用了来自德国北海海岸的一种植物的克隆插条。一组在营养液中不添加氯化钠（O组植物），另一组添加3%氯化钠（氯化钠组植物）。在一年的时间里，O组植物叶片中的钠和氯含量几乎保持在恒定的低水平。在氯化钠组植物的叶片中，钠和氯的浓度在一年中变化很大，在冬季达到最大值。钾含量始终处于低水平。耐冻性曲线在夏季最低，在冬季最高。氯化钠组和O组植物耐冻性峰值之间的微小差异表明，增加的盐胁迫对耐冻性影响不大。细胞膜中的冻害胁迫，如类囊体，与盐浓度增加的作用方式相同；因此，两者共同作用必然会放大胁迫。为了分析其离子含量，在一年中从具有不同耐冻性的叶片中以非水方式分离出海滨碱蓬的叶绿体。在冬季中期，当耐冻性最高时，氯化钠组植物的叶绿体含有约250 mM氯化物（O组植物约为150 mM），而细胞的非质体部分含有约1 M（O组植物约为400 mM）氯化物。另一方面，柠檬酸在冬季叶绿体中达到高浓度。已知柠檬酸盐等非挥发性有机酸在体外可以通过依数性补偿无机盐离子对类囊体的伤害作用（赫伯和桑塔里厄斯，1976年）。海滨碱蓬叶绿体中氯化物和柠檬酸盐的摩尔比例随着耐冻性的增加而降低，达到了在体外对叶绿体膜具有保护作用的值。海滨碱蓬体内的这种关系为细胞膜依数性保护的概念提供了证据。除了柠檬酸盐，苹果酸盐也可能作为一种依数性保护剂，抵御冻害放大的盐胁迫。
