Aslam M, Oaks A, Huffaker R C
Department of Biology, McMaster University, Hamilton, Ontario, Canada, L8S 4K1.
Plant Physiol. 1976 Oct;58(4):588-91. doi: 10.1104/pp.58.4.588.
Barley seedlings grown in the dark with 10 mm KNO(3) have low levels of nitrate reductase activity even though large amounts of No(3) (-) accumulate in the leaves. When the leaves are excised and transferred to the light, there is an increase in nitrate reductase activity both in the presence and absence of exogenous NO(3) (-). When the leaves are transferred to a glucose solution (0.05 m) but kept in the dark, induction of nitrate reductase activity occurs only when fresh NO(3) (-) is added to the system.In dark-grown leaves, there are small traces of NO(3) (-) in a "metabolic pool." Addition of glucose does not alter this distribution. Light, on the other hand, results in an appreciable accumulation of NO(3) (-) in the metabolic pool. There is a linear correlation between nitrate reductase activity and the size of the metabolic NO(3) (-) pool. Our results thus suggest that NO(3) (-) accumulates in a storage pool when seedlings are grown in continuous darkness. The transfer of this NO(3) (-) to an active metabolic pool is mediated by light but not by glucose. We believe that this transfer of NO(3) (-) leads to the induction of nitrate reductase. When NO(3) (-) is included in the medium, both light and glucose increase its incorporation into the metabolic pool. The results suggest two mechanisms for regulating the metabolic NO(3) (-) pool: (a) a transfer from the storage pool which requires light; and (b) a transfer from the external medium which requires either glucose or light.
在黑暗中用10 mM硝酸钾培养的大麦幼苗，即使叶片中积累了大量的硝酸根离子，其硝酸还原酶活性水平仍很低。当叶片被切除并转移到光照条件下时，无论是否存在外源硝酸根离子，硝酸还原酶活性都会增加。当叶片转移到葡萄糖溶液（0.05 m）中但保持在黑暗中时，只有向系统中添加新鲜的硝酸根离子，才会诱导硝酸还原酶活性。在黑暗生长的叶片中，“代谢池”中存在少量的硝酸根离子痕迹。添加葡萄糖不会改变这种分布。另一方面，光照会导致代谢池中硝酸根离子明显积累。硝酸还原酶活性与代谢性硝酸根离子池的大小之间存在线性关系。因此，我们的结果表明，当幼苗在连续黑暗中生长时，硝酸根离子会在储存池中积累。这种硝酸根离子向活性代谢池的转移是由光介导的，而不是由葡萄糖介导的。我们认为这种硝酸根离子的转移会导致硝酸还原酶的诱导。当培养基中含有硝酸根离子时，光照和葡萄糖都会增加其向代谢池中的掺入。结果表明了两种调节代谢性硝酸根离子池的机制：（a）从储存池转移，这需要光照；（b）从外部培养基转移，这需要葡萄糖或光照。
