FLUORIDE-INDUCED RESPONSES IN THE CHLOROPHYLL CONTENT AND THE ANTIOXIDANT SYSTEM IN TEA LEAVES (CAMELLIA SINENSIS)

Experiments were performed to study the effects of different fluoride ion (F) concentrations (0, 1, 5, 10, 20, and 50 mg/L) on the chlorophyll content and the antioxidant system (enzymatic and non-enzymatic antioxidants) in tea leaves. The chlorophyll content in the tea leaves remained relatively stable when the concentrations of F were within 1-10 mg/L but reduced significantly when the F concentrations were >= 20 mg/L. Increased F-induced stress led to an increase in the release of superoxide anion (O-center dot(2)-), indicating that the tea leaves were stressed by oxidation with a positive correlation between F concentration and oxidative stress. Lower concentrations of F (1-5 mg/L) increased the activities of superoxide dismutase (SOD), peroxidase (POD), glutathione reductase (GR), glutathione peroxidase (GPX) and dehydroascorbate reductase (DHAR) in the tea leaves, whereas higher concentrations inhibited their activities. Ascorbic acid (AsA) and reduced glutathione (GSH) remained relatively stable at lower F concentrations, but decreased at higher F concentrations. The results indicated that both the enzymatic and non-enzymatic antioxidant systems in the tea leaves would provide adequate protection against oxidative stress induced by lower F concentrations but that higher F concentrations led to an imbalance between the generation and elimination of reactive oxygen species (ROS).