Cantón F R, Suárez M F, Josè-Estanyol M, Cánovas F M
Laboratorio de Bioquímica y Biología Molecular, Facultad de Ciencias-Instituto Andaluz de Biotecnología, Universidad de Málaga, Spain.
Plant Mol Biol. 1999 Jul;40(4):623-34. doi: 10.1023/a:1006219205062.
The expression of a cytosolic glutamine synthetase (GS1; EC 6.3.1.2) gene was examined in cotyledons of Scots pine seedlings. Light strongly stimulated GS1 mRNA accumulation during development. Similarly, steady-state levels of GS1 transcripts increased in dark-grown seedlings transferred to light and decreased in dark-adapted seedlings. Light/dark adaptation affected rbcS and lhcb2 mRNA levels and chlorophyll contents in the same manner. Light-grown seedlings in the presence of the herbicide norflurazon showed a drastic decrease in mRNA for GS and photosynthetic proteins, whereas the effect of the herbicide on mitochondrial beta-ATP synthase mRNA was limited. These results indicate that factors associated with developing chloroplasts could be required for maximal GS1 gene expression during seedling development. The level of GS polypeptide, determined by immunoblot, was up-regulated during seedling development in the light or dark. However, the levels of the polypeptide detected were unaltered by the light/dark adaptation treatments. The analysis of GS1 mRNA association with polysomes indicated that the discrepancies between GS protein and mRNA levels are not a result of a differential translational rate of the transcript in darkness relative to light. Two GS isoproteins with different isoelectric point were resolved by two-dimensional PAGE in light- and dark-germinated plants. The relative abundance of one of them was markedly affected by light and correlated with the observed changes in GS mRNA, suggesting that the other form is not a product derived from the detected transcript. In situ hybridization of cotyledon sections showed the presence of GS1 mRNAs in mesophyll and phloem cells confirming gene expression in photosynthetic tissues. High levels of transcript were detected also in meristematic cells of apical primordia. These data suggest a dual role for the GS1 gene associated with chloroplast development/activity and glutamine biosynthesis for nitrogen mobilization during early growth of Scots pine.
在欧洲赤松幼苗的子叶中检测了胞质谷氨酰胺合成酶（GS1；EC 6.3.1.2）基因的表达。在发育过程中，光照强烈刺激GS1 mRNA的积累。同样，转移到光照下的暗生长幼苗中GS1转录本的稳态水平增加，而暗适应幼苗中则降低。光/暗适应以相同方式影响rbcS和lhcb2 mRNA水平以及叶绿素含量。在存在除草剂氟草敏的情况下，光照生长的幼苗中GS和光合蛋白的mRNA急剧下降，而除草剂对线粒体β -ATP合酶mRNA的影响有限。这些结果表明，与发育中的叶绿体相关的因子可能是幼苗发育过程中GS1基因最大表达所必需的。通过免疫印迹测定的GS多肽水平在光照或黑暗条件下的幼苗发育过程中上调。然而，检测到的多肽水平不受光/暗适应处理的影响。GS1 mRNA与多核糖体结合的分析表明，GS蛋白和mRNA水平之间的差异不是转录本在黑暗和光照下翻译速率不同的结果。通过二维PAGE在光照和黑暗萌发的植物中分离出两种具有不同等电点的GS同工蛋白。其中一种的相对丰度受光照显著影响，并且与观察到的GS mRNA变化相关，这表明另一种形式不是来自检测到的转录本的产物。子叶切片的原位杂交显示在叶肉和韧皮部细胞中存在GS1 mRNA，证实了光合组织中的基因表达。在顶端原基的分生细胞中也检测到高水平的转录本。这些数据表明，GS1基因在欧洲赤松早期生长过程中与叶绿体发育/活性以及氮素动员的谷氨酰胺生物合成相关，具有双重作用。
