Study of the effect of fluorine and lead on the metabolism of lichens: case of the species Xanthoriaparietina(L.) Th. Fr.

Abstract

Our work aims to investigate the toxicity of fluorine and lead on various stress parameters onlichen species ofXanthoriaparietina (L.) Th. Fr., chlorophyll, proteins and antioxidant system,to explore the differences in polyphenol and flavonoid contentsand to study the antibacterial activity of its methanol extract.For this purpose, lichen thalli have been treated by sodium fluoride (NaF) and lead nitrate (Pb(NO3)2)at concentrations of 0, 0.5, 1.0, 5.0 and 10 mM, for time scale 0, 24, 48 and 96 h. The obtained results revealed that all the evaluated parameters showed significant variations compared to the controls, it was noted that chlorophyll a (Ca), chlorophyll b (Cb), total chlorophyll (Ca+b) and protein contents decreased correlating with exposure times and/or increasing concentrations of NaF and Pb(NO3)2, with a significant increase of Ca/b ratio showing that Cb is more affected than Ca and that this degradation is coupled with pheophytin accumulation. However,contents of catalase, hydrogen peroxide (H2O2), Glutathione (GSH), proline, Malondialdehide (MDA), soluble sugarsincreased with increasing exposure time and/or increasing concentrations of NaF and Pb(NO3)2. The results also showed that high concentration of NaF and Pb(NO3)2 solutions disturbed the detoxification system, resulting in total glutathione decomposition and reduction of polyphenol and flavonoid contents. Furthermore, results indicate a favorable relationship between differences in the diameter of the inhibitory zone and the polyphenol and flavonoid levels. In light of these results, Gram-positive bacteria were found to be more sensitive to extracts than Gram-negative bacteria.