Nitric oxide synthase-mediated early nitric oxide-burst alleviates drought-induced oxidative damage in ammonium supplied-rice roots

Ammonium (NH 4 + ) can enhance rice drought tolerance in comparison to nitrate (NO 3 - ). The mechanism underpinning this relationship was investigated based on the time-dependent nitric oxide (NO) production and its protective role in oxidative stress of NH 4 + -/NO 3 - -supplied rice under drought. An early burst of NO was induced by drought 3h after root NH 4 + treatment but not after NO 3 - treatment. Root oxidative damage induced by drought was significantly higher in NO 3 - than in NH 4 + -treatment due to its reactive oxygen species accumulation. Inducing NO production by applying NO donor 3h after NO 3 - treatment alleviated the oxidative damage, while inhibiting the early NO burst increased root oxidative damage in NH 4 + treatment. Application of nitric oxide synthase (NOS) inhibitor N(G)-nitro- L -arginine methyl ester (L-NAME) completely suppressed NO synthesis in roots 3h after NH 4 + treatment and aggravated drought-induced oxidative damage, indicating the aggravation of oxidative damage might have resulted from changes in NOS-mediated early NO burst. Drought also increased root antioxidant enzymes activities, which were further induced by NO donor but repressed by NO scavenger and NOS inhibitor in NH 4 + -treated roots. Thus, the NOS-mediated early NO burst plays an important role in alleviating oxidative damage induced by drought by enhancing antioxidant defenses in NH 4 + -supplied rice roots. Highlight NOS-mediated early NO burst plays an important role in alleviating oxidative damage induced by water stress, by enhancing the antioxidant defenses in roots supplemented with NH 4 +