AOBPreview published online on April 11, 2007
Annals of Botany, doi:10.1093/aob/mcm051
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Responses of Rice Cultivars with Different Nitrogen Use Efficiency to Partial Nitrate Nutrition
College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, 210095, PR China
* For correspondence. E-mail shenqirong{at}njau.edu.cn
Received: 24 November 2006 Returned for revision: 11 December 2006 Accepted: 8 February 2007
Background and Aims: There is increased evidence that partial nitrate (NO3) nutrition (PNN) improves growth of rice (Oryza sativa), although the crop prefers ammonium (NH4+) to NO3 nutrition. It is not known whether the response to NO3 supply is related to nitrogen (N) use efficiency (NUE) in rice cultivars.
Methods: Solution culture experiments were carried out to study the response of two rice cultivars, Nanguang (High-NUE) and Elio (Low-NUE), to partial NO3 supply in terms of dry weight, N accumulation, grain yield, NH4+ uptake and ammonium transporter expression [real-time polymerase chain reaction (PCR)].
Key Results: A ratio of 75/25 NH4+-N/NO3-N increased dry weight, N accumulation and grain yield of Nanguang by 30, 36 and 21 %, respectively, but no effect was found in Elio when compared with those of 100/0 NH4+-N/NO3-N. Uptake experiments with 15N-NH4+ showed that NO3 increased NH4+ uptake efficiency in Nanguang by increasing Vmax (14 %), but there was no effect on Km. This indicated that partial replacement of NH4+ by NO3 could increase the number of the ammonium transporters but did not affect the affinity of the transporters for NH4+. Real-time PCR showed that expression of OsAMT1s in Nanguang was improved by PNN, while that in Elio did not change, which is in accordance with the differing responses of these two cultivars to PNN.
Conclusions: Increased NUE by PNN can be attributed to improved N uptake. The rice cultivar with a higher NUE has a more positive response to PNN than that with a low NUE, suggesting that there might be a relationship between PNN and NUE.
Key words: Ammonium transporter, partial NO3 nutrition, NH4+ uptake, nitrogen use efficiency, rice, Oryza sativa