Salicylic Acid-Altering Arabidopsis Mutants Response to NO2 Exposure

Nitrogen dioxide (NO2)-induced responses in wild type (wt) and salicylic acid (SA)-altering Arabidopsis mutants snc1 (suppressor of npr1-1, constitutive) with high SA level, transgenic line nahG with low SA level, npr1-1 (nonexpressor of PR gene) with SA signaling blockage and double mutant snc1nahG plants, were investigated. All mutant lines except sncl showed that NO2 exposure at 0.25 μL L−1 increased chlorophyll content and biomass accumulation, elevated photosynthetic rate, and decreased MDA content compared to their respective controls. The sncl plants were similar to the control plants for these measured indices. NO2 exposure at 0.5 μL L−1 and higher doses caused injury to wt, nahG, npr1-1 and snc1nahG plants, whereas the snc1 plants exhibited a stronger tolerance. To evaluate the resistance mechanism, we further investigated the changes in the mutants exposed to 1 μL L−1 of NO2 in relation to endogenous SA level, antioxidant capacity and redox status. The collected data demonstrated that the NO2 tolerance in snc1, with a high SA level, was tightly linked to the increased antioxidant capacity and decreased oxidative stress. This suggests that SA may play an important protective function in plant response to NO2 stress.