甘露醇对渗透胁迫下的鱼腥藻(Anabaena)固氮活性的增效作用

外源甘露醇可在一定程度上增强鱼腥藻Anabaenasp．7120固氮的抗渗透胁迫能力．厌氧（Ar中）、能量供应受阻（暗处理、添加ATP形成的抑制剂）、合成固氮酶蛋白所需物质供应不足（单加N2不加CO2）以及分子氧下，甘露醇的有益作用减小或消失，反之（正常光照、通气环境、提高CO2浓度，同时供应H2和O2或CO2和N2）则这一作用增大。渗透胁迫下，外源蔗糖对甘露醇支持蓝藻固氮的作用不明显。

ENHANCING EFFECT OF MANNITOL ON NITROGEN FIXATION ACTIVITY IN ANABAENA UNDER OSMOTIC STRESS

The experiments showed that the osmotic stress-induced inhibition of nitrogen fixation activity was mitigated to some extent by the introduction of mannitol into culture solution in Anabaena sp. strain 7120. It was shown that under dark condition or in the presence of photosynthetic inhibitors, such as DNP or CCCP, the beneficial effect of mannitol on nitrogen fixation activity was weakened or didrinished in Anabaena. Higher nitrogen fixation activity was observed in experiments with mannitol by adding O2 together with Hi, but the activity was depressed by adding O2 alone. When Anabaena cells submitted to osmotic stress were incubated in aerobic conidition (in air) the beneficial effect of mannitol was higher than that in anaerobic condition (in Ar or Nc. Beneficial effect of mannitol on nitrogen fixation activity of Anabaena was obviously strengthened by preincubation with 5% CO2 or with 5% CO2 plus 40% N2, but it was abated by adding N2 only. The mannitol-supported nitrogen fixation aCtivity in Anabaena was less evident in the presence of exogenous sucrose.