生物谷报道：众所周知，“氮”、“磷酸”、“钙”是作物生长的三大营养素。缺乏这些营养素的话，就不能培育出水稻、小麦等农作物和美丽的兰花等观赏性植物。虽然这些营养素都是由植物的根来吸收的，但其具体结构还是一个谜。
RIKEN植物科学研究中心的基础代谢研究小组与德国霍恩海姆大学共同合作，弄清了植物作为氮源，向细胞内吸收土壤中的“氨态氮”时铵输送体的作用。氨态氮是由微生物分解土壤中含有动植物遗骸和排泄物的蛋白质与尿酸、尿素等做出的氮源。
在植物的根部，“AMT1型”铵输送体选择性地使铵离子运送到细胞内。特别是在氮肥料不足时，AMT1型铵输送体就会发挥这个作用。研究小组使用拟南芥的基因剔除植物弄清了4种AMT1型铵输送体的机能，阐明了其中3种是吸收氨态氮的重要物质。这个成果将对提高作物的氮利用率的技术开发起到帮助，同时，在改善由于作物吸收不完而使过剩营养素流出田地污染环境的问题上也将作为一个有用成果。
这是由RIKEN植物科学研究中心(主任 筱崎一雄)基础代谢研究小组的高桥秀树组长与德国霍恩海姆大学的Nicolaus von Wiren教授共同研究的成果。
本研究成果刊登于美国科学杂志The Plant Cell (8月号)。（援引日本理化学研究所）
原始出处:
Plant Cell Preview
Published on August 10, 2007; 10.1105/tpc.107.052134
Received April 9, 2007
Returned for revision July 13, 2007
Accepted July 23, 2007
The Organization of High-Affinity Ammonium Uptake in Arabidopsis Roots Depends on the Spatial Arrangement and Biochemical Properties of AMT1-Type Transporters
Lixing Yuan 1, Dominique Loqué 1, Soichi Kojima 1, Sabine Rauch 1, Keiki Ishiyama 2, Eri Inoue 2, Hideki Takahashi 2, and Nicolaus von Wirén 1*
1 Molecular Plant Nutrition, Institute of Plant Nutrition, University of Hohenheim, D-70593 Stuttgart, Germany
2 RIKEN Plant Science Center, Yokohama 230-0045, Japan
* To whom correspondence should be addressed. E-mail: vonwiren@uni-hohenheim.de .
The AMMONIUM TRANSPORTER (AMT) family comprises six isoforms in Arabidopsis thaliana. Here, we describe the complete functional organization of root-expressed AMTs for high-affinity ammonium uptake. High-affinity influx of 15N-labeled ammonium in two transposon-tagged amt1;2 lines was reduced by 18 to 26% compared with wild-type plants. Enrichment of the AMT1;2 protein in the plasma membrane and localization of AMT1;2 promoter activity in the endodermis and root cortex indicated that AMT1;2 mediates the uptake of ammonium entering the root via the apoplasmic transport route. An amt1;1 amt1;2 amt1;3 amt2;1 quadruple mutant (qko) showed severe growth depression under ammonium supply and maintained only 5 to 10% of wild-type high-affinity ammonium uptake capacity. Transcriptional upregulation of AMT1;5 in nitrogen-deficient rhizodermal and root hair cells and the ability of AMT1;5 to transport ammonium in yeast suggested that AMT1;5 accounts for the remaining uptake capacity in qko. Triple and quadruple amt insertion lines revealed in vivo ammonium substrate affinities of 50, 234, 61, and 4.5 µM for AMT1;1, AMT1;2, AMT1;3, and AMT1;5, respectively, but no ammonium influx activity for AMT2;1. These data suggest that two principle means of achieving effective ammonium uptake in Arabidopsis roots are the spatial arrangement of AMT1-type ammonium transporters and the distribution of their transport capacities at different substrate affinities.
