Effect Of Hexavalent Chromium [Cr(?)] On Phytoremediation Potential And Physiological Response Of Hybrid Napier Grass With And Without EDTA Application

Anthropogenic activities and the geogenic release have become contributing factors in increasing the level of soil and ground water Cr???contamination and has become an emergent concern in the recent years.The present study investigated the effects of varying Cr???concentrations(0,20,40 and 60 mg kg^-1 soil)with and without EDTA application on Cr accumulation,growth,photosynthetic efficiency,basic elemental status and oxidative stress defense mechanism in hybrid Napier grass?Pennisetum americanum x Pennisetum purpureum Schumach?.The results revealed that Cr???stress significantly reduced the growth and photosynthetic efficiency of hybrid Napier grass,significantly increased MDA level and the activities of antioxidant enzymes?SOD,POD and CAT?in their root and shoot and altered concentration of N and S in their root and shoot.Cr concentrations in root and shoot of hybrid Napier grass linearly increased with increasing soil Cr concentration.Cr accumulation was higher in roots than in shoots.Bioaccumulation factor of root significantly decreased and that of shoot significantly increased in dose dependent manner.The chlorophyll concentration and the values of maximum quantum yield?Fv/Fm?,the inferred oxygen evolving complex activity?Fv/Fo,where Fv,is Fm-Fo?,effective photochemical quantum yield of PSII??PSII?,electron transport?ETR?and photochemical quenching?qP?significantly decreased and non-photochemical fluorescence quenching?qN?significantly increased with increasing Cr concentrations.The phytotoxic effects of Cr in hybrid Napier grass were associated with oxidative stress as evidenced by increased MDA level and the activities of antioxidant enzymes?SOD,POD and CAT?in root and shoot with increasing soil Cr concentrations.The phytotoxic effects of Cr were slightly higher in EDTA-treated plants compared with non-EDTA treated plants.FTIR data confirmed the ICP-AES results and revealed that Cr interacts with amide,hydroxyl,phosphate,and carboxyl groups in plant sample.In conclusion,the present study indicated that the elevation of Cr concentration significantly increased Cr accumulation in root and shoot of hybrid Napier grass which negatively affected their growth.The Cr???stress altered the levels of N and S,reduced chlorophyll content,and impaired photosynthetic machinery associated with reduced tolerance and increased oxidative stress.In addition,EDTA application further enhanced Cr uptake and accumulation.Moreover,the phytotoxic effects of Cr???increased in the presence of EDTA than without EDTA treatment.Although the Cr???stress reduced tolerance,but even at the highest Cr concentration,the plant could evidenced strong resistance by increasing antioxidants SOD,POD and CAT.The hybrid Napier grass might be classified as Cr excluder because of its ability to limit the accumulation of Cr in shoot?TF<1?.Moreover,due to its BAF>1 and TF<1,this plant would be applicable for Cr phytostabilization.Furthermore,hybrid Napier grass is fodder crop;its ability to limit the accumulation of Cr in shoot would prevent animal's ingestion,control soil mobility,and stop the entry of Cr into the food chain.Moreover,the FTIR data demonstrated that the Cr binding involved hydroxyl,carboxyl,amide and phosphate groups in the plant tissues.