[Effect of Cr(VI) stress on growth of three herbaceous plants and their Cr uptake]

In order to elucidate the toxic mechanisms of Trifolium repens, Festuca arundinacea and Medicago sativa under chromium [Cr (VI)] stress, provide a theoretic foundation for phytoremediation of Cr-contaminated soil, pot experiment was conducted to investigate the effects of Cr(VI) on plant growth, physiological characteristics, Cr accumulation and distribution in three herbaceous plants. Soil sample was treated by adding K2Cr2O7 with the Cr(VI) concentration of 0, 100, 200, 300 and 400 mg x kg(-1), respectively. The results indicated that the average tolerance indices of T. repens, F. arundinacea and M. sativa were 62.5, 48.3 and 36.33, respectively. Compared with control group, contents of chlorophyll, the activity of superoxide dismutase(SOD) and peroxidase (POD) were 57.14%, 51.51%, 35.76% and 63.27%, 52.96%, 41.36% in T. repens, and F. arundinacea, respectively, but M. sativa died in 400 mg x kg(-1) Cr(VI) treatment. The plant height, root length, dry mass of roots and shoots decreased under Cr(VI) stress in three herbaceous plants, and M. sativa > F. arundinacea > T. repens, however, the content of malonyldialdehyde (MDA) increased compared to the control, and the variation range of M. sativa was the highest, while T. repens was the smallest among them. The tolerance of Cr( VI) was T. repens > F. arundinacea > M. sativa. Cr mainly distributed in cell wall and then in the cytoplasm, and less distributed in the mitochondrion and chloroplast in leaves of three herbaceous plants, whereas the content of chlorophyll, MDA, the activity of SOD and POD correlated well with Cr accumulation in the mitochondrion and chloroplast. Cr concentration in the subcellular of leaves increased with the adding Cr(VI) concentration,and M. sativa > F. arundinacea > T. repens. In comparison with T. repens, F. arundinacea, Cr concentration in the leaves of M. sativa was the maximal, i.e. 51.44 mg x kg(-1), and the proportions in the mitochondrion (18.04%) and chloroplast (19.09%) were also higher in 300 mg x kg(-1) Cr(VI). The average accumulation factors of shoots/roots were 1.22/1.54, 1.16/1.44 and 1.26/1.62, while the average translocation factors were 0.78, 0.78 and 0.74 in T. repens, F. arundinacea and M. sativa, respectively. The results suggest that T. repens and F. arundinacea are promising for the phytoremediation of Cr-contaminated soil.