Nitrate inhibits the remobilization of cell wall phosphorus under phosphorus-starvation conditions in rice (Oryza sativa)

The rice cultivars ‘Kasalath’ (Kas) and ‘Nipponbare’ (Nip) were used to demonstrate that the nitrogen source NO₃⁻ inhibits internal phosphorus (P) reutilization in rice under P-absence conditions. Analysis using Kas showed that the expression of-P-induced marker genes OsIPS1/2 and OsSPX1/2/3/5 are significantly higher under 1 mM NO₃⁻-P (1N-P) treatment than 0 mM NO₃⁻-P (0N-P) treatment. The absence of NO₃⁻ from the nutrient solution significantly increased cell wall P release by increasing pectin synthesis and increasing the activity of pectin methylesterase (PME), and also significantly improved the translocation of soluble P from the root to the shoot by increasing xylem sap P content under P-absence conditions. The rice seedlings grown in 0 mM NO₃⁻ accumulated significantly higher nitric oxide (NO) in the roots than those grown in 1 mM NO₃⁻. Exogenously applying the NO donor sodium nitroprusside (SNP) revealed that NO is a major contributor to differential cell wall P remobilization in rice by mediating pectin synthesis and demethylation under different NO₃⁻ concentrations (0 and 1 mM) under P-deprived conditions.