SUMMARY
The assessment of the air quality is a major concern to the current time. The monitoring and maintenance of air quality necessarily pass by detecting and estimating the overall air pollution. The use of lichens must be an assessmenttool to be studied. In our work we were interested about the toxicity of lead on the various parameters of stress in the lichen Xanthoria parietina. For this purpose, lichen thalli have been incubated at lead concentrations of 0, 0.5, 1.0, 5.0 and 10.0 mM, for time scale of 0, 24, 48 and 96 hours. The obtained results showed that lead has an action on the various studied parameters, and the intensity of oxidative stress observed in lichens thalli depends on the concentration, and time of exposure. Lead induced a decrease in chlorophyll and protein contents, and an increase in the contents of catalase, hydrogen peroxide and reduced glutathione. Furthermore, the results also showed that high concentrations of lead caused total destruction of reduced glutathione.