Eisele R, Ullrich W R
Botanisches Institut der Technischen Hochschule, D-6100 Darmstadt, Germany.
Plant Physiol. 1977 Jan;59(1):18-21. doi: 10.1104/pp.59.1.18.
In Ankistrodesmus braunii, in the absence of CO(2), i.e. in CO(2)-free air or N(2), photosynthetic nitrate uptake and nitrate reduction were inhibited, especially at low pH. Under such conditions, glucose stimulated nitrate uptake and reduction to almost the same level in the pH range between 6 and 8.5. CO(2) at 0.03% effected an intermediate pH dependence of nitrate uptake; saturating CO(2) concentration (more than 1%) eliminated the pH dependence, as did glucose, but the rates were enhanced compared with glucose. Glucose and, even more, CO(2), drastically reduced the release of nitrite and ammonia to the medium, the stoichiometry between alkalinization of the medium and nitrate uptake (OH(-)/NO(3) (-)) approached 1.Due to the lack of storage vacuoles in Ankistrodesmus, nitrate uptake and nitrate reduction were closely coupled processes whose experimental separation is difficult. The relieving effect of glucose and CO(2) suggests a carrier-mediated nitrate uptake which is more limiting than nitrate reduction and is sensitive to low pH, but which is stabilized by some intermediate originating from an active carbon metabolism.
在布朗栅藻（Ankistrodesmus braunii）中，在没有二氧化碳的情况下，即在无二氧化碳的空气或氮气中，光合性硝酸盐吸收和硝酸盐还原受到抑制，尤其是在低pH值时。在这种条件下，葡萄糖在pH值6至8.5范围内刺激硝酸盐吸收和还原至几乎相同的水平。0.03%的二氧化碳使硝酸盐吸收呈现出中等程度的pH依赖性；饱和二氧化碳浓度（超过1%）消除了pH依赖性，葡萄糖也有同样效果，但与葡萄糖相比，速率有所提高。葡萄糖，甚至更多的二氧化碳，极大地减少了亚硝酸盐和氨向培养基中的释放，培养基碱化与硝酸盐吸收之间的化学计量比（OH(-)/NO(3) (-)）接近1。由于布朗栅藻缺乏储存液泡，硝酸盐吸收和硝酸盐还原是紧密耦合的过程，其实验分离很困难。葡萄糖和二氧化碳的缓解作用表明存在一种载体介导的硝酸盐吸收，它比硝酸盐还原更具限制性，且对低pH敏感，但可由源自活跃碳代谢的某些中间产物稳定。
