摘要
陆生蓝藻发菜(Nostoc flagelliforme)固氮酶活性的最适温度为21—28℃;最适藻丝体含水量为1000—1500%;最大饱和光强达150—200焦耳/m^2·秒。在湿润状态下,发菜对较高的温度很敏感。在45℃下1小时,发菜固氮酶失掉活性。在干燥状态下,发菜在55℃高温下,每天5小时,放置21天后,其固氮酶活性保持不变。预先培养4—5天的湿发菜对干燥变得敏感;但在干湿交替循环中,其固氮酶活性逐步提高,并明显地改善了它对干燥的抵抗能力。此外,在高盐浓度下(0.17—0.43mol/LNaCl)发菜的固氮酶活性被强烈地抑制,说明它不能耐盐碱。发菜的固氮生理特性是它对荒漠草原生态条件适应的结果。干湿交替循环或许是发菜维持生存的必需条件。
The optimal temperature for the nitrogenase activity in the terrestrial cyanobacterium N. flaglliforme was 21—28℃;the optimal water content in thallus was 1000—1500%;the light saturation was between 150—200 J·m^(-2)·s^(-1).The thallus of N.flagelliforme is extremely sen- sitive to higher temperature in wet.Long-term exposure of wetted thallus to high temperature at 45℃ causes rapid declination of its nitrogenase activity to zero.Under dry condition,N. flagelliforme is extremely resistant to extensive desiccation and heat exposure.Dry thalli ex- posed to 55℃,5 hours daily for 21 days,show no marked change in its nitrogenase activity. The thalli preincubated in wet condition for 4—5 days,are highly sensitive against desication. However,repeated drying/wetting cycles induce a slow and gradual increase of its nitrogenase activity and improve the resistance of its nitrogenase activity against desiccation.High con- centrated NaCl salt solution(0.17—0.43 mol/L)depletes nitrogenase activity of the thalli qu- ickly.Above result shows that N.flogelliforme is not able to resist against salt.The phy- siological characteristics of nitrogen fixation of cyanobacterium N.flagelliforme may be con- sidered as a result of drought adaptation of the terrestrial ecological condition and the dry- ing/westting cycle is perhaps a necessary factor to maintain its growth.
关键词
含水量
温度
环境因素
发菜
Environmental factors
Nitrogen fixation
Nostoc flagelliforme
