Riens B, Heldt H W
Institut für Biochemie der Pflanze, Universität Göttingen, Untere Karspüle 2, 3400 Göttingen, Germany.
Plant Physiol. 1992 Feb;98(2):573-7. doi: 10.1104/pp.98.2.573.
In leaves of spinach plants (Spinacia oleracea L.) performing CO(2) and NO(3) (-) assimilation, at the time of sudden darkening, which eliminates photosystem I-dependent nitrite reduction, only a minor temporary increase of the leaf nitrite content is observed. Because nitrate reduction does not depend on redox equivalents generated by photosystem I activity, a continuation of nitrate reduction after darkening would result in a large accumulation of nitrite in the leaves within a very short time, which is not observed. Measurements of the extractable nitrate reductase activity from spinach leaves assayed under standard conditions showed that in these leaves the nitrate reductase activity decreased during darkening to 15% of the control value with a half-time of only 2 minutes. Apparently, in these leaves nitrate reductase is very rapidly inactivated at sudden darkness avoiding an accumulation of the toxic nitrite in the cells.
在进行二氧化碳和硝酸根离子同化作用的菠菜植株（菠菜）叶片中，当突然遮光从而消除依赖光系统I的亚硝酸盐还原作用时，仅观察到叶片中亚硝酸盐含量有轻微的短暂增加。由于硝酸盐还原不依赖于光系统I活性产生的氧化还原当量，遮光后硝酸盐还原作用的持续会导致叶片在很短时间内大量积累亚硝酸盐，但并未观察到这种情况。在标准条件下测定菠菜叶片中可提取的硝酸还原酶活性，结果表明，在这些叶片中，遮光期间硝酸还原酶活性降至对照值的15%，半衰期仅为2分钟。显然，在这些叶片中，突然遮光时硝酸还原酶会非常迅速地失活，从而避免细胞中有毒亚硝酸盐的积累。
