Masclaux-Daubresse Céline, Carrayol Elisa, Valadier Marie-Hélène
Unité de Nutrition Azotée des Plantes, Institut National de la Recherche Agronomique, Route de St-Cyr, 78026 Versailles Cedex, France.
Planta. 2005 Jun;221(4):580-8. doi: 10.1007/s00425-004-1468-2. Epub 2005 Jan 15.
In tobacco, the two enzymes of nitrogen metabolism, cytosolic glutamine synthetase (GS1; E.C.6.3.1.2) and glutamate dehydrogenase (GDH; E.C.1.4.1.2), are induced during leaf senescence, whereas the chloroplastic glutamine synthetase (GS2; E.C.6.3.1.2) and nitrate reductase (NR; E.C.1.6.1.1) are repressed in the course of ageing. In this report, we showed in discs of fully expanded Nicotiana tabacum L. cv. Xanthi leaves that sucrose (Suc) and amino acids were involved in the regulation of the expression of GS1 and GDH genes. Suc induced the expression of GS1 and repressed that of GDH. Therefore, we concluded that in response to Suc, GS1 behaved as an "early" Senescence Associated Gene (SAG), whereas GDH behaved as a "late" SAG. Moreover, amino acids induced the expression of both genes. Among the amino acids tested as signal molecules, proline (Pro) and glutamate (Glu) were major inducers of GDH and GS1 expression, respectively. Interestingly, an opposite regulation of GS1 and GS2 by Pro and Glu was shown. The contrary effect of Suc on NIA (NR encoding gene) and GDH mRNA accumulation was also emphasized.
在烟草中,氮代谢的两种酶,即胞质谷氨酰胺合成酶(GS1;E.C.6.3.1.2)和谷氨酸脱氢酶(GDH;E.C.1.4.1.2),在叶片衰老过程中被诱导,而叶绿体谷氨酰胺合成酶(GS2;E.C.6.3.1.2)和硝酸还原酶(NR;E.C.1.6.1.1)在衰老过程中受到抑制。在本报告中,我们在完全展开的烟草(Nicotiana tabacum L. cv. Xanthi)叶片圆片中表明,蔗糖(Suc)和氨基酸参与了GS1和GDH基因表达的调控。蔗糖诱导了GS1的表达并抑制了GDH的表达。因此,我们得出结论,响应蔗糖时,GS1表现为“早期”衰老相关基因(SAG),而GDH表现为“晚期”SAG。此外,氨基酸诱导了这两个基因的表达。在作为信号分子测试的氨基酸中,脯氨酸(Pro)和谷氨酸(Glu)分别是GDH和GS1表达的主要诱导剂。有趣的是,脯氨酸和谷氨酸对GS1和GS2表现出相反的调控作用。蔗糖对NIA(硝酸还原酶编码基因)和GDH mRNA积累的相反作用也得到了强调。