Abstract
Increasing evidence shows that partial nitrate nutrition (PNN) can be attributed to improved plant growth and nitrogen-use efficiency (NUE) in rice. Nitric oxide (NO) is a signalling molecule involved in many physiological processes during plant development and nitrogen (N) assimilation. It remains unclear whether molecular NO improves NUE through PNN. Two rice cultivars (cvs Nanguang and Elio), with high and low NUE, respectively, were used in the analysis of NO production, nitrate reductase (NR) activity, lateral root (LR) density, and (15)N uptake under PNN, with or without NO production donor and inhibitors. PNN increased NO accumulation in cv. Nanguang possibly through the NIA2-dependent NR pathway. PNN-mediated NO increases contributed to LR initiation, (15)NH₄(+)/(15)NO₃(-) influx into the root, and levels of ammonium and nitrate transporters in cv. Nanguang but not cv. Elio. Further results revealed marked and specific induction of LR initiation and (15)NH₄(+)/(15)NO₃(-) influx into the roots of plants supplied with NH₄(+)+sodium nitroprusside (SNP) relative to those supplied with NH₄(+) alone, and considerable inhibition upon the application of cPTIO or tungstate (NR inhibitor) in addition to PNN, which is in agreement with the change in NO fluorescence in the two rice cultivars. The findings suggest that NO generated by the NR pathway plays a pivotal role in improving the N acquisition capacity by increasing LR initiation and the inorganic N uptake rate, which may represent a strategy for rice plants to adapt to a fluctuating nitrate supply and increase NUE.
Highlights
Nitrogen (N) nutrition affects all levels of plant functions, including metabolism resource allocation, growth, and development (Crawford, 1995; Stitt, 1999)
Further results revealed marked and specific induction of lateral root (LR) initiation and 15NH4+/15NO3– influx into the roots of plants supplied with NH4++sodium nitroprusside (SNP) relative to those supplied with NH4+ alone, and considerable inhibition upon the application of cPTIO or tungstate (NR inhibitor) in addition to partial nitrate nutrition (PNN), which is in agreement with the change in Nitric oxide (NO) fluorescence in the two rice cultivars
The findings suggest that NO generated by the nitrate reductase (NR) pathway plays a pivotal role in improving the N acquisition capacity by increasing LR initiation and the inorganic N uptake rate, which may represent a strategy for rice plants to adapt to a fluctuating nitrate supply and increase nitrogenuse efficiency (NUE)
Summary
Nitrogen (N) nutrition affects all levels of plant functions, including metabolism resource allocation, growth, and development (Crawford, 1995; Stitt, 1999). Plants have the potential to adapt to dramatic fluctuations in N availability by modulating their nutrient acquisition capacity and by altering their metabolism and morphology, such as their root architecture (Crawford, 1995; López-Bucio et al, 2003; Song et al, 2013a; Manoli et al, 2014). Our understanding of how plants sense external nitrate conditions and the signal transduction system that influences root system development and nutrient acquisition capacity remains limited. Nitric oxide (NO) is a signalling molecule involved in many physiological processes during plant development and nutrient assimilation. Correa-Aragunde et al (2004) suggested that auxin and NO are involved in a linear signalling pathway during the LR formation process in tomato. The mechanisms of NO-regulated N uptake in response to nitrate fluctuation remain poorly understood
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