Cock J M, Brock I W, Watson A T, Swarup R, Morby A P, Cullimore J V
Department of Biological Sciences, University of Warwick, Coventry, UK.
Plant Mol Biol. 1991 Oct;17(4):761-71. doi: 10.1007/BF00037059.
Glutamine synthetase (GS) activity increased over three-fold in developing primary leaves of Phaseolus vulgaris L. This increase was shown to be the result of differential expression of three members of the GS gene family: gln-alpha and gln-beta, which encode cytosolic GS polypeptides, and gln-delta, which encodes the chloroplast-located GS. The gln-delta gene was the most highly expressed GS gene and was regulated in a complex manner with two different transcripts accumulating differentially during leaf development. This gene was expressed weakly in the dark and was induced strongly by light; this induction was shown not to be an indirect effect of photorespiration. In the long term, gln-delta showed increased expression in photorespiring compared with non-photorespiring leaves. However, in the short term, there was no induction of gln-delta following transfer of plants to photorespiratory conditions. These results suggest that regulation of gln-delta by photorespiration was the result of indirect, long-term effects on cellular metabolism. In general, in all these experiments, analysis of cytosolic versus chloroplastic GS polypeptides and of the GS isoenzyme profiles showed the same pattern of changes in abundance as that observed for the mRNAs suggesting that regulation of GS gene expression occurred primarily at the mRNA level. However, it was noteworthy that the delta isoenzyme remained at a high abundance in older leaves, grown in both light and dark, despite a decrease in abundance of gln-delta mRNA.
谷氨酰胺合成酶（GS）活性在菜豆初生叶发育过程中增加了三倍多。这种增加被证明是GS基因家族三个成员差异表达的结果：gln-α和gln-β编码胞质GS多肽，gln-δ编码定位于叶绿体的GS。gln-δ基因是表达量最高的GS基因，其调控方式复杂，在叶片发育过程中有两种不同的转录本差异积累。该基因在黑暗中表达较弱，受光强烈诱导；这种诱导并非光呼吸的间接作用。从长期来看，与非光呼吸叶片相比，gln-δ在光呼吸叶片中表达增加。然而，在短期内，将植物转移到光呼吸条件下后，gln-δ并没有被诱导。这些结果表明，光呼吸对gln-δ的调控是对细胞代谢间接的长期影响的结果。总体而言，在所有这些实验中，对胞质与叶绿体GS多肽以及GS同工酶谱的分析显示，其丰度变化模式与mRNA的变化模式相同，这表明GS基因表达的调控主要发生在mRNA水平。然而，值得注意的是，尽管gln-δ mRNA丰度下降，但δ同工酶在光下和暗中生长的老叶中仍保持高丰度。
