Pre-exposure to nitric oxide modulates the effect of ozone on oxidative defenses and volatile emissions in lima bean

The roles that ozone and nitric oxide (NO), the chief O₃ precursor, play in the antioxidative balance and inducible volatile emissions of lima bean were assessed. Exposure to O₃ inhibited APX, CAT, and GR, decreased GSH content and induced emissions of (E)-β-ocimene, limonene, 1,8-cineole, linalool, (E)-4,8-dimethyl-1,3,7-nonatriene (E)-DMNT, 2-butanone and nonanal. O₃ did not induce emissions of (E)-β-caryophyllene and appeared to reduce the antioxidative capacity of plants to a greater extent than NO and NO followed by O₃ (NO/O₃) treatments. There were significant differences in emissions of (E)-β-ocimene and linalool between NO/O₃ treated plants and controls, but no differences in antioxidant concentrations. A model to explain the relationships between the ascorbate-glutathione cycle and O₃ and NO inducible volatiles was proposed. Our findings suggest that prior exposure to NO modulates the oxidative effect of ozone by the process of cross-tolerance, which might regulate the antioxidative system and induction of volatile organic compounds.