Enhanced sensitivity to oxidative stress in an Arabidopsis nitric oxide synthase mutant

The possible involvement of nitric oxide (NO) in oxidative stress tolerance was studied using Arabidopsis thaliana wild type (WT) and Atnos1 mutant plants, in which endogenous NO production is greatly diminished because 80% of nitric oxide synthase (NOS) activity is eliminated due to T-DNA insertion in the first exon of the NOS1 gene. Compared with WT, Atnos1 mutant plants showed increased hypersensitivity to salt stress and methyl viologen (MV) treatment. The maximal photochemical efficiency of photosystem II (Fv/Fm) and membrane integrity decreased in WT and Atnos1 mutant plants under stresses, but the extent was higher in the mutant. Treatment with sodium nitroprusside (SNP) (a NO donor) to Atnos1 mutant plants alleviated the damage. Instead, inhibition of nitric oxide accumulation in the WT plants produced opposite effects. Hydrogen peroxide and lipid peroxidation increased and the extent was higher in Atnos1 mutant plants than that in WT plants under MV stress. These results indicated that nitric oxide could protect the damage against NaCl and MV treatments.