EDTA-enhanced lead phytoremediation in sunflower (Helianthus annuus L.) hydroponic culture

The aim of the present study was to investigate the capability of Sunflower (Helianthus annuus L.) to tolerate and accumulate high amount of lead (Pb) and propose it for soil phytoremediation. To this regard, plants were grown in hydroponics and treated with different Pb concentrations (10 to 160 mu M) and a fixed concentration (500 mu M) EDTA (ethylene diamine tetra acetic acid) for 14 and 28 days (d). Effects on total biomass production, photosynthetic pigments and protein contents as well as the quantities of non protein thiols (NP-SH), glutathione (GSH), phytochelatins (PCs) and activity of glutathione reductase (GR) were estimated. Results revealed that roots (575 mu g g(-1) DW) and shoots (135 mu g g(-1) DW) accumulated Pb after 28 d of exposure, however, addition of EDTA enhanced the Pb accumulation in roots (645 mu g g(-1) DW) and shoots (255 mu g g(-1) DW). Exposure of Pb (28 d) registered a significant (P<0.05) reduction in growth parameters and induction of phytochelatins (P<0.05; r=0.26) plus some of the important antioxidants (P<0.05; r=0.42), which were positively correlated to metal accumulation. Sunflower exposed at 40 mu M of Pb for 28 d synthesized higher quantity of PC2 (18.5 fold) and PC3 (10.5 fold), as compared to control. However, the results showed that addition of EDTA resulted in low toxicity compared to Pb alone. These data support the capability of H. annuus L. to accumulate and tolerate significant quantity of Pb and its utility for phytoremediation. This is because of the plant has the capacity to combat metal induced oxidative stress via significant synthesis of NP-SH, GSH and high activity of GR, as it would provide sufficient GSH not only for PCs synthesis but also for antioxidant function.