Immunolocalization of glutamine synthetase in senescing tobacco (Nicotiana tabacum L.) leaves suggests that ammonia assimilation is progressively shifted to the mesophyll cytosol
Immunolocalization of glutamine synthetase in senescing tobacco (Nicotiana tabacum L.) leaves suggests that ammonia assimilation is progressively shifted to the mesophyll cytosol
复制标题
DOI：
10.1007/s004250000309
复制
发表时间：
2000-09-01
期刊：
影响因子：
4.3
通讯作者：
Hirel, B
中科院分区：
文献类型：
--
作者：
Brugière, N;Dubois, F;Hirel, B
谷氨酰胺合成酶（GS）在氨和谷氨酸依赖atp的反应中催化谷氨酰胺的形成（谷氨酰胺是巨人体内氮运输的主要形式），这种酶存在于质体和/或细胞质中，取决于所检查的植物或器官。为了了解GS同工酶在叶片氮素再动员中的作用，我们研究了烟草（Nicotiana tabacum L.）自然衰老过程中GS同工酶的定位。随着叶片衰老的进程，衰老叶片叶肉细胞质中GS多肽含量增加，而韧皮部伴生细胞中GS蛋白含量显著降低。衰老叶片细胞质中GS多肽的存在似乎是Gln1-3基因诱导的结果，该基因的转录本在成熟叶片中未检测到，但在衰老叶片中含量丰富。总之，我们的研究结果表明，在衰老过程中，氨同化逐渐从叶绿体转移到叶肉细胞的细胞质。
Glutamine synthetase (GS) catalyses the formation of glutamine (a major form of nitrogen transport in giants) in an ATP-dependent reaction using ammonium and glutamate, This enzyme is present in the plastids and/or in th cytosol depending on the plant or the organ examined. In order to understand the role of GS isoforms in the remobilization of leaf nitrogen, we studied the localization of GS isoenzymes during natural senescence of tobacco (Nicotiana tabacum L.) leaves. Parallel to the progression of leaf senescence, an increase in cytosolic GS polypeptides was detected in the mesophyll cytosol of senescing leaves while a significant decrease in GS protein content was observed in the phloem companion cells. The presence of GS polypeptides in the leaf cytosol of senescing leaves appears to be the result of an induction of the Gln1-3 gene, the transcripts of which are not detected in mature leaves but are abundant in senescing leaves. Alltogether, our results suggest that during senescence, ammonia assimilation is progressively shifted from the chloroplasts to the cytosol of leaf mesophyll cells.