Responses of rice cultivars with different nitrogen use efficiency to partial nitrate nutrition

Background and Aims There is increased evidence that partial nitrate (NOD nutrition (PNN) improves growth of rice (Oryz sativa), although the crop prefers ammonium (NH4+) to NO3- nutrition. It is not known whether the a 4 3 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 trans porter 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 0, 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 15 N-NH4+ showed that NO3- increased NH4+ uptake efficiency in 'Nanguang' by increasing V-max (14 %), but there was no effect on K-m. 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 OsAMTls 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.