[Effects of elevated ozone concentrations on reactive oxygen metabolism and related gene expression in Ginkgo biloba leaves]

By using the open top chambers (OTCs) fumigation method, this paper investigated the changes of foliar injury, level of reactive oxygen species (ROS), activities and gene expression of antioxidant enzymes in Ginkgo biloba leaves under different ozone (ambient ozone≈40, 80, 160, 200 nmol·mol^-1) concentrations, in order to study the effects of elevated ozone (O₃) concentrations on reactive metabolism. The results showed that the obvious foliar injuries were observed in 160 and 200 nmol·mol^-1 O₃ treatments, while no visible injury was observed in 80 nmol·mol^-1 O₃ and ambient O₃ treatments. After 20 d, a significant increase in O₂^-· generation rate was observed in G. biloba leaves exposed to 160, 200 nmol·mol^-1 O₃, compared with ambient ozone and 80 nmol·mol^-1 O₃, and there were no significant differences between ambient O₃ and 80 nmol·mol^-1 treatments. After 40 d, H₂O₂ content of G. biloba leaves in 160 and 200 nmol·mol^-1 O₃ was significantly higher than that in 80 nmol·mol^-1 and ambient ozone, respectively. The activities of catalase (CAT) in 160 and 200 nmol·mol^-1 treatments were also significantly higher than that in 80 nmol·mol^-1 and ambient O₃ treatments. The ascorbate peroxidase (APX) activity of leaves for each elevated O₃ treatment was lower than that of ambient ozone. The level of CAT and APX expression increased progressively after 40 d O₃ treatment. The expression intensity of GbD was conspicuously strengthened along with the increase of ozone concentration and fumigation time. Le-vel of reactive oxygen increased, activities of antioxidant enzyme decreased, level of gene expression down-regulated, and foliar visible injury was observed in leaves of G. biloba in elevated ozone stress.

[Effects of elevated Cd, Zn and their combined effects on antioxidant system of tobacco]

A solution culture was conducted to study the effects of elevated Cd and/or Zn ions (0.1 mmol·L-1 Cd2+, 0.15 mmol·L-1 Zn2+, 0.1 mmol·L-1 Cd2++0.15 mmol·L-1Zn2+) on seed germination rate and reactive oxygen species (ROS) level, antioxidants contents, antioxidant enzyme activities and product of membrane lipid peroxidation in tobacco seedling leaves. The results showed that compared to control, the seed germination rate decreased under elevated level of Cd2+or Zn2+, the superoxide radical (O2-· ) generation rate and hydrogen peroxide (H2O2) content in tobacco seedlings increased, the activities of catalase (CAT), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDAR), and glutathione reductase (GR) increased, content of glutathione (GSH) and GSH/GSSG (oxidized glutathione) ratio decreased, and malondialdehyde (MDA) content increased. Compared to elevation of the level of only Cd2+ or Zn2+, the seed germination rate under elevation of both Cd2+ and Zn2+ levels was enhanced significantly; O2-· generation rate, contents of H2O2 and MDA decreased; CAT, APX and MDAR activities increased in the last stage of Cd2+ and Zn2+ exposure. Heavy metal Cd2+ or Zn2+ could induce the physiological injury to tobacco seedlings, and the toxic effects increased with prolonged stress time. The combined treatment of Cd and Zn could alleviate the toxicity of single stress on tobacco seedlings.