| In order to identify the toxic mechanism of plant under chromium (Cr) stress,provide theoretic foundation for phytoremediation of Cr-contaminated soil,pot experiment was conducted to investigate the effects of heavy metal Chromium［Cr(Ⅵ)］stress on the emergence rate,the biomass of seedlings,the contents of chlorophyll,malonyldialdehyde (MDA),the activities of superoxide dismutase (SOD),peroxide enzyme (POD),Cr subcellular distribution in the leaves and Cr uptake in Brassica juncea.The results indicated that the emergence rate of seedlings,the biomass and the chlorophyll content of B.juncea were increased under lower Cr(Ⅵ) concentrations.However,lower emergence rate,biomass and chlorophyll content were observed for the higher Cr(Ⅵ) concentrations.The content of malonyldialdehyde (MDA) was reverse with increased Cr(Ⅵ) concentration,and there was significantly negative correlation between MDA and Chlorophyll content.The activities of SOD and POD were increased under 300 mg/kg Cr(Ⅵ),but the activities of SOD and POD were decreased above 300 mg/kg Cr(Ⅵ).Cr was mainly distributed in the cytoplasm of leaves (48.57%-64.77%，41.03%-76.42%,respectively)and the second in the cell wall,and less distributed in the mitochondrion and chloroplast(＜10%) in Laifengjiecai and Sichuanhuangzi.Sichuanhuangzi could accumulate more Cr in leaves than Laifengjiecai from the Cr-contaminated soil.As compared to Laifengjiecai,Sichuanhuangzi has stronger tolerance to Cr(Ⅵ) pollution.The Cr contents in stem,leaf and root of B.juncea usually were heightened with increased concentrations of Cr(Ⅵ) in soil.Average Cr concentration in the leaves of Laifengjiecai and Sichuanhuangzi were167.30 and 197.60 mg/kg,respectively for 70 days growing in the soil spiked with 300 mg/kg Cr(Ⅵ)， the maximum of Cr content in plant shoots were 1.71 and 2.81mg/plant,respectively,namely,Cr removed by plant shoots were 0.23% and 0.38% of Cr content in treated soil,respectively.The results suggest that Sichuanhuangzi is promising for the phytoremediation of Cr-contaminated soil. |
