Mishra A K, Singh Satya S
Department of Botany, Banaras Hindu University, Varanasi, India.
Acta Biol Hung. 2006 Sep;57(3):355-65. doi: 10.1556/ABiol.57.2006.3.9.
Protection from salt stress was observed in the terms of yield (fresh and dry weight, chlorophyll and protein) and nitrogenase activity. Azollapinnata appeared highly sensitive to 40 mM external NaCl stress. Fronds of Azolla unable to grow beyond a concentration of 30 mM NaCl and accordingly death was recorded at 40 mM NaCl on the 6th day of incubation. Yield was inhibited by various levels of NaCl (0, 10, 20 and 30 mM). Addition of combined-N to the growth medium protected the association partially from salt toxicity. Among the N-sources (NO3-, NH4+ and urea) tried, urea mitigated the salt-induced toxicity most efficiently. Reduction in nitrogenase activity was observed when intact Azolla was grown in nutrient medium either supplemented with different levels of NaCl or combined nitrogen. Only NO3- (5 mM) protected the enzymatic activity from salt toxicity while other concentrations of ammonium, nitrate and urea slowed down the salt-induced inhibition of enzyme activity in Azolla-Anabaena association. These results suggested that an optimum protection from salt stress could be obtained by using a combination of combined nitrogen sources. The reason for this protection might be due to the availability of combined nitrogen to the association, nitrogen is only available through the biological nitrogen fixation which is the most sensitive to salt stress.
从产量（鲜重和干重、叶绿素和蛋白质）以及固氮酶活性方面观察到了对盐胁迫的保护作用。细绿萍对40 mM的外部NaCl胁迫表现出高度敏感性。在30 mM NaCl浓度以上，细绿萍的叶状体无法生长，因此在培养第6天，40 mM NaCl处理下记录到细绿萍死亡。不同水平的NaCl（0、10、20和30 mM）均抑制了产量。向生长培养基中添加化合态氮可部分保护共生体免受盐毒性影响。在所尝试的氮源（NO3-、NH4+和尿素）中，尿素缓解盐诱导毒性的效率最高。当完整的细绿萍在添加不同水平NaCl或化合态氮的营养培养基中生长时，观察到固氮酶活性降低。只有5 mM的NO3-能保护酶活性免受盐毒性影响，而其他浓度的铵、硝酸盐和尿素会减缓盐诱导的细绿萍-鱼腥藻共生体中酶活性的抑制。这些结果表明，通过使用化合态氮源组合可获得对盐胁迫的最佳保护。这种保护的原因可能是由于共生体可获得化合态氮，因为氮仅通过对盐胁迫最敏感的生物固氮作用获得。
