Objective: To study the oxidative stress and antioxidative response of Cinnamomum camphora seedlings exposed to nitrogen dioxide (NO(2)) fumigation.
Methods: Measurements were made up of the growth, chlorophyll content, chlorophyll fluorescence, antioxidant system and lipid peroxidation of one-year-old C. camphora seedlings exposed to NO(2) (0.1, 0.5, and 4 microl/L) fumigation in open top chambers over a period of 60 d.
Results: After the first 30 d, 0.5 and 4.0 microl/L NO(2) showed insignificant effects on the growth of C. camphora seedlings. However, exposure to 0.5 and 4.0 microl/L NO(2) for 15 d significantly reduced their chlorophyll content (P<0.05), enhanced their malondialdehyde (MDA) content and superoxide dismutase (SOD) activity (P<0.05), and also significantly reduced the maximal quantum yield of PSII in the dark [the ratio of variable fluorescence to maximal fluorescence (F(v)/F(m))] (P<0.05). In the latter 30 d, 0.5 microl/L NO(2) showed a positive effect on the vitality of the seedlings, which was reflected by a recovery in the ratio of F(v)/F(m) and chlorophyll content, and obviously enhanced growth, SOD activity, ascorbate (AsA) content and glutathione reductase (GR) activity (P<0.05); 4.0 microl/L NO(2) then showed a negative effect, indicated by significant reductions in chlorophyll content and the ratio of F(v)/F(m), and inhibited growth (P<0.05).
Conclusion: The results suggest adaptation of C. camphora seedlings to 60-d exposure to 0.1 and 0.5 microl/L NO(2), but not to 60-d exposure to 4.0 microl/L NO(2). C. camphora seedlings may protect themselves from injury by strengthening their antioxidant system in response to NO(2)-induced oxidative stress.