Journal Article

Dynamic Interactions between Root NH<sub>4</sub><sup>+</sup> Influx and Long-Distance N Translocation in Rice: Insights into Feedback Processes

Herbert J. Kronzucker, Jan K. Schjoerring, Yair Erner, Guy J.D. Kirk, M. Yaeesh Siddiqi and Anthony D.M. Glass

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 39, issue 12, pages 1287-1293
Published in print December 1998 | ISSN: 0032-0781
Published online December 1998 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/oxfordjournals.pcp.a029332
Dynamic Interactions between Root NH4+ Influx and Long-Distance N Translocation in Rice: Insights into Feedback Processes

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Ammonium influx into roots and N translocation to the shoots were measured in 3-week-old hydroponically grown rice seedlings (Oryza sativa L., cv. IR72) under conditions of N deprivation and NH4+ resupply, using 13NH4+as a tracer. Root NH4+ influx was repressed in plants continuously supplied with NH4+ (at 0.1 mM), but a high proportion of absorbed N (20 to 30%) was translocated to the shoot in the form of N assimilates during the 13-min loading and desorption periods. Interruption of exogenous NH4+ supply for periods of 1 to 3 d caused NH4+ influx to be de-repressed. This same treatment caused N translocation to the shoot to decline rapidly, until, by 24 h, less than 5% of the absorbed 13N was translocated to the shoot, illustrating a clear priority of root over shoot N demand under conditions of N deprivation. Upon resupplying 1 mM NH4+, root NH4+ influx responded in a distinct four-phase pattern, exhibiting periods in which NH4+ influx was first enhanced and subsequently reduced. Notably, a 25 to 40% increase in root influx, peaking at ˜2 h following re-exposure was correlated with a 4- to 5-fold enhancement in shoot translocation and a repression of root GS activity. The transient increase of NH4+ influx was also observed in seedlings continuously supplied with NO3 and subsequently transferred to NH4+. Extended exposure to NH4+ caused root NH4+ influx to decrease progressively, while shoot translocation was restored to ˜30% of incoming NH4+. The nature of the feedback control of NH4+ influx as well as the question of its inducibility are discussed.

Keywords: Ammonium; Influx; Nitrogen; Nitrogen stress; N-13; Rice

Journal Article.  0 words. 

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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