Cock J M, Mould R M, Bennett M J, Cullimore J V
Department of Biological Sciences, University of Warwick, Coventry, England, UK.
Plant Mol Biol. 1990 Apr;14(4):549-60. doi: 10.1007/BF00027500.
In this paper we have examined whether the four glutamine synthetase (gln) genes, expressed in roots and nodules of Phaseolus vulgaris are substrate-inducible by ammonium. Manipulation of the ammonium pool in roots, through addition and removal of exogenous ammonium, did not elicit any changes in the abundances of the four mRNAs thus suggesting that the gln genes in roots of this legume are neither substrate-inducible by ammonium nor derepressed during nitrogen starvation. In nodules the effect of the ammonium supply on expression of the gln genes has been examined by growing nodules under argon/oxygen atmospheres, or with a number of Fix- Rhizobium mutants, and following addition of exogenous ammonium. The results of these experiments suggest that the expression of the gln-gamma gene, which is strongly induced during nodule development, is primarily under a developmental control. However nitrogen fixation appears to have a quantitative effect on expression of gln-gamma as the abundance of this mRNA is about 2 to 4-fold higher under nitrogen-fixing conditions. This effect could not be mimicked by addition of exogenous ammonium and moreover is not specific to the gln-gamma gene as mRNA from a leghaemoglobin gene was similarly affected. Taken together these results have failed to find an effect of ammonium on specifically inducing the expression of glutamine synthetase genes in roots and nodules of P. vulgaris.
在本文中，我们研究了菜豆根和根瘤中表达的四个谷氨酰胺合成酶（gln）基因是否受铵底物诱导。通过添加和去除外源铵来调控根中的铵库，并未引起这四种mRNA丰度的任何变化，这表明这种豆科植物根中的gln基因既不受铵底物诱导，也不在氮饥饿期间去阻遏。在根瘤中，通过在氩/氧气氛下培养根瘤，或与一些固氮缺陷型根瘤菌突变体一起培养，并添加外源铵后，研究了铵供应对gln基因表达的影响。这些实验结果表明，在根瘤发育过程中强烈诱导表达的gln-γ基因，主要受发育控制。然而，固氮似乎对gln-γ基因的表达有定量影响，因为在固氮条件下，这种mRNA的丰度大约高2至4倍。添加外源铵无法模拟这种效应，而且这种效应并非gln-γ基因所特有，因为来自豆血红蛋白基因的mRNA也受到类似影响。综合这些结果，未能发现铵对菜豆根和根瘤中谷氨酰胺合成酶基因表达的特异性诱导作用。
