Elevated NO₂ induces leaf defensive mechanisms in Bougainvillea spectabilis seedlings

With a growing economy, the living standard of people has improved which has led to increased use of urban motor vehicles globally. Consequently, the concentration of nitrogen dioxide (NO₂) has increased in the ambient air, becoming a major pollutant in urban areas. Plant leaves can absorb, adsorb and fix nitrogen oxides to some extent. Interestingly, NO₂ has been recognized as a positive/negative regulator of plant growth. To comprehensively understand the effect of NO₂-induced pollution on plants, Bougainvillea spectabilis seedlings were fumigated with different concentrations of nitrogen dioxide (NO₂) for a short period in the current study. Further, the induced morphological, physiological, and biochemical changes were measured in the treated as well as untreated seedlings. NO₂ exposure caused yellow-brown spotting on the leaf blades in B. spectabilis, which could be the symptoms of oxidative damage. Our findings also reflected the changes in antioxidant enzyme activity and peroxidation of membrane lipids. In addition, the levels of osmotic regulatory substances were also found to be altered to different degrees. In addition, the activities of nitrogen metabolism-related enzymes varied, mainly affecting amino acid metabolism. Overall, the current study would provide a theoretical and scientific basis for selecting and allocating plants in NO₂-contaminated areas to manage the pollutants level.