Ishiyama K, Hayakawa T, Yamaya T
Department of Applied Biological Chemistry, Faculty of Agriculture, Tohoku University, Sendai, Japan.
Planta. 1998 Mar;204(3):288-94. doi: 10.1007/s004250050258.
The mRNA and protein for NADH-dependent glutamate synthase (NADH-GOGAT; EC 1.4.1.14) in root tips of rice (Oryza sativa L. cv. Sasanishiki) plants increases dramatically within 12 h of supplying a low concentration (> 0.05 mM) of ammonium ions (T. Yamaya et al., 1995, Plant Cell Physiol 36: 1197-1204). To identify the specific cells which are responsible for this rapid increase, the cellular localization of NADH-GOGAT protein was investigated immunocytologically with an affinity-purified anti-NADH-GOGAT immunoglobulin G. When root tips (> 1 mm) of rice seedlings which had been grown for 26 d in water were immuno-stained, signals for the NADH-GOGAT protein were detected in the central cylinder, in the apical meristem, and in the primordia of the secondary roots, Signals for ferredoxin-dependent GOGAT (Fd-GOGAT; EC 1.4.7.1) protein were also seen in the same three areas. When the roots were supplied with 1 mM ammonium ions for 24 h, there were strong signals for the NADH-GOGAT protein in two cell layers of the root surface, i.e. epidermis and exodermis, in addition to the cells giving signals in the absence of ammonium ions. The supply of ammonium ions was less effective on the profile of signals for Fd-GOGAT. Although the supply of ammonium ions had less effect on the expression of cytosolic glutamine synthetase (GS; EC 6.3.1.2), this enzyme was also found to be located in the epidermis and exodermis, as well as in the central cylinder and cortex. The results indicate that NADH-GOGAT, coupled to the cytosolic GS reaction, is probably important for the assimilation of ammonium ions in the two cell layers of the root surface.
在水稻（Oryza sativa L. cv. Sasanishiki）植株根尖中，依赖NADH的谷氨酸合酶（NADH-GOGAT；EC 1.4.1.14）的mRNA和蛋白质在供应低浓度（>0.05 mM）铵离子后的12小时内急剧增加（T. Yamaya等人，1995年，《植物细胞生理学》36: 1197 - 1204）。为了确定导致这种快速增加的特定细胞，使用亲和纯化的抗NADH-GOGAT免疫球蛋白G通过免疫细胞化学方法研究了NADH-GOGAT蛋白的细胞定位。当对在水中生长26天的水稻幼苗的根尖（>1毫米）进行免疫染色时，在中柱、顶端分生组织和侧根原基中检测到NADH-GOGAT蛋白的信号。在相同的这三个区域也观察到了依赖铁氧还蛋白的GOGAT（Fd-GOGAT；EC 1.4.7.1）蛋白的信号。当根部供应1 mM铵离子24小时后，除了在无铵离子时发出信号的细胞外，在根表面的两层细胞即表皮和外皮层中也有强烈的NADH-GOGAT蛋白信号。铵离子的供应对Fd-GOGAT信号分布的影响较小。尽管铵离子的供应对胞质谷氨酰胺合成酶（GS；EC 6.3.1.2）的表达影响较小，但该酶也被发现位于表皮和外皮层以及中柱和皮层中。结果表明，与胞质GS反应偶联的NADH-GOGAT可能对根表面两层细胞中铵离子的同化很重要。
