Peat L. J., Tobin A. K.
Plant Sciences Laboratory, Sir Harold Mitchell Building, School of Biological and Medical Sciences, University of St. Andrews, St. Andrews, United Kingdom KY16 9TH.
Plant Physiol. 1996 Aug;111(4):1109-1117. doi: 10.1104/pp.111.4.1109.
Glutamine synthetase (GS) was detected by immunogold localization in the cytosol and plastids of roots of 7-d-old barley (Hordeum vulgare L. cv Klaxon) seedlings grown in the presence or absence of NO3- (15 mM) or NH4+ (30 mM). The number of GS polypeptides changed during root development, and this was affected by N nutrition. There was no evidence of a NO3--inducible root plastid GS.In apical 5- to 10-mm regions of the root the concentration of immunogold labeling of cytosolic GS was higher in the cortical parenchyma than in the vascular cells of the stele, irrespective of N nutrition. This labeling was at least 50% higher in both cell types in N-free compared with N-grown (either NO3- or NH4+) seedlings. In contrast, GS specific activity was highest in roots of NO3--grown seedlings. It is suggested that this indicates the presence of inactive GS in roots grown without N. This study has identified both cell- and development-specific responses of GS to N nutrition.
在添加或不添加15 mM NO₃⁻ 或30 mM NH₄⁺ 的条件下培养7天大麦（Hordeum vulgare L. cv Klaxon）幼苗，通过免疫金定位法在其根的细胞质和质体中检测到谷氨酰胺合成酶（GS）。GS多肽的数量在根发育过程中发生变化，且受氮素营养影响。没有证据表明根质体GS是由NO₃⁻ 诱导产生的。在根顶端5至10毫米区域，无论氮素营养状况如何，皮层薄壁细胞中细胞质GS的免疫金标记浓度均高于中柱的维管细胞。与氮素充足（NO₃⁻ 或NH₄⁺ 培养）的幼苗相比，两种细胞类型在无氮培养的幼苗中该标记至少高出50%。相反，GS比活性在NO₃⁻ 培养的幼苗根中最高。这表明在无氮培养的根中存在无活性的GS。本研究确定了GS对氮素营养的细胞特异性和发育特异性反应。
