Regulation of ammonium-mediated inhibition of root system development via local and systemic pathways
Baohai Li1, Qing Li1, Liming Xiong2, Herbert J. Kronzucker3 and Weiming Shi1,*
1State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China.
2Plant Stress Genomics Research Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia.
3Department of Biological Sciences, University of Toronto, 1265 Military Trail, Toronto, Ontario, M1C 1A4, Canada.
*Corresponding Author：Tel: (+8625) 86881566; Fax: ((+8625) 86881000; E-mail: email@example.com
The formation of root system architecture is greatly dependent on the environmental conditions such as nutrients. Ammonium (NH4+) is an important nitrogen source for higher plants. However, excess NH4+ shows a strong suppression on root system development. Here, with local nutrition supply device, we revealed that NH4+-mediated inhibition of root elongation is primarily through root tip, whereas NH4+-mediated reduction of lateral root number is a result of shoot contact with NH4+. Furthermore, NH4+ inhibition of root growth was shown to target primarily cell elongation, which was directly linked to excessive NH4+ efflux in the root elongation zone, but not related to auxin pathway. This NH4+ efflux is regulated by GDP-mannose pyrophosphorylase (GMPase). On the other hand, NH4+-induced reduction of lateral root formation results from less lateral root emergence rather than lateral root initiation, which is caused by the decreased transport of shoot-derived auxin to roots, via the auxin influx carrier AUX1. Taken together, these results suggest regulations of primary root elongation and lateral root formation by NH4+ is through local and systemic two independent pathways. Our findings provide a novel insight to regulations of root development by environmental nutrient factors.
Key Words: Ammonium; AUX1, VTC1, root system development