Effect of flavonoids on heavy metal tolerance in Arabidopsis thaliana seedlings

Arabidopsis thaliana was used to investigate possible effects of flavonoids oil heavy metal tolerance. Arabidopsis wild type (WT) and mutant lines with a defect in flavonoid biosynthesis (tt) were grown on media containing different heavy metals, and two growth parameters were evaluated. It was shown that root length and seedling weight were reduced in mutants more than in the wild type when grown oil cadmium (Cd) while on zinc (Zn) only root length was affected. As marker for heavy metal tolerance, the induction of two phytochelatin synthase genes (AtPCS1, AtPCS2) in WT and the tt5 mutant after Cd treatment was monitored by quantitative RT-PCR. The AtPCS1 transcript was induced in WT at higher Cd levels than in the mutant. In contrast, the AtPCS2 transcript was not induced under these experimental conditions in the WT, but it was induced in tt5. We then investigated whether the growth inhibition phenotype of the mutants Could be rescued by addition of flavonoids. For this, the seedlings were treated with the flavanone naringenin and the flavonol quercetin, and the same growth parameters were determined. Quercetin and naringenin induced root growth and seedling fresh weight of WT on concentrations of Zn up to 500 mu M, but this was not the case for root length of it mutants. However, seedling weight could be stimulated by flavonoids, especially in the tt5 mutant line. When the plants were grown on Cd, only the root length defect of tt5 plants Could be rescued by flavonoids. The seedling weight increased oil Cd in all lines, although to a different extent. These results are discussed with respect to the potential role of flavonoids in heavy metal tolerance.