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

研究了非豆科固氮植物（放线菌植物）与共生菌Frankia的耐盐性。本实验中使用的放线菌植物是日本自然生长的木麻黄、大叶胡颓子、赤杨和毛赤杨。从黄瓜根瘤中分离到一株有效的Frankia菌株。本试验以木贼（equisetifolia）和3个不同寄主范围的Frankia菌株（Ceql、Emal和Anil）为试验材料。Frankia菌株的生长显着抑制NaCl浓度高于100 mM，虽然耐盐性的幅度有很大的不同菌株。然而，当细胞被高浓度NaCl抑制其生长时，将其转移到不含NaCl的培养基中，它们再次进行增殖。因此，我们判断Frankia的耐盐性普遍较高。4放线根植物的种子萌发显着抑制NaCl和发芽没有发生在200 mM NaCl。这些结果表明，播种放线菌种子对盐碱地植被的恢复是无效的。A. sieboldiana和A.粗毛幼苗对盐胁迫的抵抗力极弱。另一方面，E. macrophylla具有较高的耐盐性，C.木贼表现出很强的耐盐性。在C中，用于结晶的NAD浓度的上限为300 mM。equisetifolia，100 mM在E. macrophylla和50 mM A. sieboldiana和A.结果表明，C. equisetifolia-Ceql共生系统和E. mocrophylla-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.