Marttila Salla, Saarelainen Ritva, Porali Ilkka, Mikkonen Anita
Univ. of Jyväskylä, Dept of Biology, Box 35, SF-40351 Jyväskylä, Finland;Research Laboratories, Alko Ltd, Box 350, SF-00101 Helsinki, Finland.
Physiol Plant. 1993 Aug;88(4):612-618. doi: 10.1111/j.1399-3054.1993.tb01379.x.
Glutamine synthetase (GS; EC 6.3.1.2) is a key enzyme of ammonia assimilation in higher plants. In the present study the subunit composition and localization of GS in germinating barley (Hordeum vulgare) seed have been clarified. Analysis of the GS polypeptide composition by immunoblotting revealed two different polypeptides. A and B, with a molecular mass of 42 and 40 kDa, respectively. In the scutellum subunit A was already present in the ungerminated seed and remained unchanged, whereas subunit B appeared on day 2 and increased about 5-fold during germination. Polypeptide B also appeared later during germination in the aleurone layer, roots and weakly in the etiolated shoots. By immunogold microscopy, GS was detected in the scutellum and the aleurone layer of barley seeds during germination. Subcellular localization of GS on ultrathin cryosections showed that a cytosolic isozyme was present in the scutellum. Our study confirms that only a cytosolic GS is expressed in barley seed, and its subunit composition changes during germination.
谷氨酰胺合成酶（GS；EC 6.3.1.2）是高等植物中氨同化的关键酶。在本研究中，已阐明了发芽大麦（Hordeum vulgare）种子中GS的亚基组成和定位。通过免疫印迹分析GS多肽组成，发现了两种不同的多肽，分别为A和B，分子量分别为42 kDa和40 kDa。在盾片中，亚基A在未发芽种子中就已存在且保持不变，而亚基B在第2天出现，并在发芽过程中增加了约5倍。多肽B在糊粉层、根中发芽后期也出现，在黄化苗中出现较少。通过免疫金显微镜观察，发芽过程中在大麦种子的盾片和糊粉层中检测到了GS。在超薄冰冻切片上对GS进行亚细胞定位显示，盾片中存在一种胞质同工酶。我们的研究证实，大麦种子中仅表达一种胞质GS，且其亚基组成在发芽过程中发生变化。
