Environmental stress tolerance in non-leguminous nitrogen fixing plants and symbiont Frankia

对非豆科固氮植物(放线菌植物)和共生菌Frankia的耐盐性进行了研究。本试验所用放线菌植物为日本自然生长的木麻黄、胡颓子、黑杨和粗毛木麻黄。从马尾松根瘤中分离到1株有效的Frankia菌株，并用3株寄主范围不同的Frankia菌株(Ceq1、Emal和Anil)进行了实验。当盐浓度高于100 mM时，Frankia菌株的生长受到明显抑制，但不同菌株的耐盐性有很大差异。然而，当被高浓度盐抑制生长的细胞转移到不含盐的培养基中时，它们又进行了增殖。因此，我们判断Frankia的耐盐性通常相当高。4种放线菌植物的种子萌发受到盐的明显抑制，200 mM的盐不能萌发。这些结果表明，播种放线菌种子不能有效地恢复盐碱地的植被。马尾松和马尾松幼苗对盐胁迫的抵抗力极弱。另一方面，大叶桉具有较高的耐盐性，木麻黄具有很强的耐盐性。马尾松结瘤的NAD浓度上限为300 mM，大叶麻黄为100 mM，马尾松和马尾松为50 mM，因此，马尾松-CEQL共生系统和马尾松-Emal共生系统有利于盐碱地植被的恢复。

Salt tolerance of non-leguminous nitrogen fixing plants (actinorhizal plants) and the symbiont Frankia was investigated. Actinorhizal plants used in this experiment were Casuarina equisetifolia, Elaeagnus macrophylla, Alnus sieboldiana and Alnus hirsuta, which are growing in Japan naturally. One effective Frankia strain was isolated from the root nodules of C. equisetifolia and 3 Frankia strains (Ceql, Emal and Anil) whose host range is different were used in this experiment. The growth of Frankia strains was markedly suppressed by NaCl concentration higher than 100 mM, although the magnitude of salt tolerance considerably differed among strains. However, when the cells depressed their growth by high NaCl concentration were transferred to the medium which did not contain NaCl, they underwent multiplication again. Accordingly, we judged that salt tolerance of Frankia is generally considerably high. Seed germination of 4 actinorhizal plants was markedly inhibited by NaCl and germination did not occur at 200 mM NaCl. These results suggested that sowing of actinorhizal plant seeds is not effective for the recovery of the vegetation in salt-accumulated lands. A. sieboldiana and A. hirsuta seedlings was extremely weak against salt stress. On the other hand, E. macrophylla possessed a pretty high salt tolerance, and C. equisetifolia showed was very strong salt tolerance. The upper limit of Nad concentration for nodulation was 300 mM in C. equisetifolia, 100 mM in E. macrophylla and 50 mM in A. sieboldiana and A. hirsuta.From these results, we concluded that C. equisetifolia-Ceql symbiotic system and E. mocrophrylla-Emal symbiotic system are useful for the recovery of the vegetation in salt-accumulated lands.