Fig. 6. Cellular ROS levels and gene expression levels of antioxidant enzymes. (A) ROS levels in cells exposed to 0–800 mg L^–1 terpinolene were measured by the NBT (3,3′-(3,3′-dimethoxy-4,4′-biphenylene)bis[2-(4-nitrophenyl)-5-phenyl-2H-tetrazolium chloride) assay. ROS generation of cells was determined as absorbance of reduced NBT at 620 nm in a microplate reader and expressed as normalized NBT reduction compared to the control group. (B and C) mRNA levels of SOD1 and GPx1 in cells exposed to 0–800 mg L^–1 were measured by RT-PCR. Values are presented as mean ± SEM. Statistical analysis was made to compare experimental groups and the control group. Significantly different values are indicated by asterisks (One-way ANOVA, *p < 0.05, **p < 0.01, ***p < 0.001). Values were taken from at least three independent biological replicas (n = 3).