Differential response of rice genotypes to nitrogen availability is associated with the altered nitrogen metabolism and ionomic balance

Abstract

Nitrogen (N) uptake and its assimilation are crucial steps for plant growth and productivity. Plant's N balance largely depends on nitrate (NO3-) and ammonium (NH4+) forms present in the rhizosphere. Due to the fluctuating and heterogeneous availability of these N forms in the soils, plants encounter low to N deficiency. In contrast to low nitrogen, high N in the form of ammonium (NH4+) severely hampers plant development and causes NH4+ toxicity. In this study, we assessed eleven rice genotypes under sufficient (SN) and low N (LN) conditions. From the analysis, we identified a rice genotype, PB1, which is hypersensitive to SN and showed reduced root and shoot growth. In contrast to the SN condition, PB1 showed improved growth performance under the LN condition. Our data show that compromised growth of PB1 under SN condition is associated with increased activity of N responsive genes such as OsAMT1.1, OsAMT2.3, OsAMT3.1 and OsAMT3.2, OsNRT1.1A and OsNRT1.1B. Strikingly, LN treatment improved the root and shoot biomass with a concomitant increase in levels of NO3- and NH4+ transporter genes along with an increase in shoot: root NO3- ratio. Additionally, we show that increased levels of N in PB1 under SN condition are associated with the enhanced activity of the GS-GOGAT pathway. Further, our ionomic analysis highlighted the role of N-defined Fe accumulation which is partially associated with the N toxicity. Taken together, our study led to identifying a rice genotype (Oryza sativa L.) which is associated with enhanced N levels and assimilation and could be used for raising N use efficient rice varieties using breeding approaches.