Abstract
BackgroundNutrition with ammonium (NH4+) can enhance the drought tolerance of rice seedlings in comparison to nutrition with nitrate (NO3−). However, there are still no detailed studies investigating the response of nitric oxide (NO) to the different nitrogen nutrition and water regimes. To study the intrinsic mechanism underpinning this relationship, the time-dependent production of NO and its protective role in the antioxidant defense system of NH4+- or NO3−-supplied rice seedlings were studied under water stress.ResultsAn early NO burst was induced by 3 h of water stress in the roots of seedlings subjected to NH4+ treatment, but this phenomenon was not observed under NO3− treatment. Root oxidative damage induced by water stress was significantly higher for treatment with NO3− than with NH4+ due to reactive oxygen species (ROS) accumulation in the former. Inducing NO production by applying the NO donor 3 h after NO3− treatment alleviated the oxidative damage, while inhibiting the early NO burst by applying the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO) increased root oxidative damage in NH4+ treatment. Application of the nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester(L-NAME) completely suppressed NO synthesis in roots 3 h after NH4+ treatment and aggravated water stress-induced oxidative damage. Therefore, the aggravation of oxidative damage by L-NAME might have resulted from changes in the NOS-mediated early NO burst. Water stress also increased the activity of root antioxidant enzymes (catalase, superoxide dismutase, and ascorbate peroxidase). These were further induced by the NO donor but repressed by the NO scavenger and NOS inhibitor in NH4+-treated roots.ConclusionThese findings demonstrate that the 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 NH4+.
Highlights
Nutrition with ammonium (NH4+) can enhance the drought tolerance of rice seedlings in comparison to nutrition with nitrate (NO3−)
Root endogenous nitric oxide (NO) production and histochemical analyses of oxidative damage To investigate whether NO participates in water stress acclimation, endogenous NO levels in roots were monitored with the NO-specific fluorescent probe diaminofluorescein-FM diacetate (DAF-FM Diaminofluorescein-FM diacetate (DA)) [25]
Significant differences in endogenous NO production were observed in roots after 48 h of water stress (Fig. 2a)
Summary
Nutrition with ammonium (NH4+) can enhance the drought tolerance of rice seedlings in comparison to nutrition with nitrate (NO3−). Results: An early NO burst was induced by 3 h of water stress in the roots of seedlings subjected to NH4+ treatment, but this phenomenon was not observed under NO3− treatment. Root oxidative damage induced by water stress was significantly higher for treatment with NO3− than with NH4+ due to reactive oxygen species (ROS) accumulation in the former. Water stress increased the activity of root antioxidant enzymes (catalase, superoxide dismutase, and ascorbate peroxidase). These were further induced by the NO donor but repressed by the NO scavenger and NOS inhibitor in NH4+-treated roots. The accumulation of ROS in water-stressed plants impairs the function of biochemical processes, damages organelles, and results in cell death [11]. Endogenous NO production may enhance plant antioxidant capacity and help plant cells survive under various types of stress
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