| Phytoremediation, the use of plants and their associated microbe for environmental cleanup, has gained advance in the past 10 years as cost-effective, noninvasive alternative technology. Willows were used for the in situ decontamination of soils polluted with Cd, Zn. Salix matsudana, S. integra and S. babylonica are native to china, and they hold high biomass, fast growth and good tolerance of wet soils. S. integra and S. babylonica for Cd, S.integra for Zn metal resistance and accumulation were studies in this paper. S. matsudana was used as material, effects on photosynthesis and mineral nutrition under Cd stress, tolerance and detoxification mechanisms to Cd were investigated. This paper was consisted of 8 parts.1. Three varieties of S. integra in hydroponic experiments for their metal resistance and accumulation were investigated. Plants were exposed to Cd (0, 10, 50μmol·L-1) for 6 weeks. Plant biomass, Cd tolerance and accumulation pattern in shoots and roots varied between varieties. 10μmol·L-1 and 50μmol·L-1 Cd treatments reduced the dry mass of shoots and roots, the leaf: root ratios for Cd in all varieties were <1, But total amount of Cd in shoot: in root were highly significantly >1, ratios of total amount of Cd decreased with Cd level in the medium. Tolerance index (TIroot) of Weshanhu variety was 0.620.82, Dahongtou variety had a TIroot of 0.88, TIroot of Yizhibi was about 0.920.93.Varieties of S. integra on zinc were evaluated with three Zn levels (0, 100, 1000μmol·L-1) for 41d. Stem heighten, root length, biomass of shoots and roots of three varieties decreased significantly with high Zn concentration (1000μmol·L-1). At 100μmol?L Zn, uptake and accumulation of three varieties shoots on Zn is highest. Zinc concentration in roots was elevated with Zn level in the medium, ratio of shoots to roots Zn concentration was near to 1 at 100μmol·L-1, Index tolerance of three warieties reduced with Zn concentration.Cadmium uptake and tolerance potential of three weeping willow (Salix babylonica) clones were evaluated with three Cd level (0, 10, 50μmo·L-1). There were not significantly difference on Cd concentration of shoots among clones, at 10μmol·L-1, Cd concentration in shoots of three clones was >100μg?g-1, and total amount of Cd in shoots to Cd in roots ratio was >1. Three clones tolerance index were related to Cd concentration in medium. 2. Salix matsudana exposed to 5 and 25μmol·L-1 of Cd for 21d in hydroponic culture were analyzed with level of lipid peroxide, ion leakage and antioxidative enzymes in roots and leaves. Electrical conductivity of leaves, K+ efflux of roots and level of lipid peroxidation of roots and leaves were not significantly influenced under Cd treatment. Changes in antioxidant enzyme levels in roots and leaves were examined, high levels of Cd(25μmol·L-1) enhanced significantly the activity of SOD in roots, Cd-induced SOD in leaves were showed more at 25μmol·L-1 than 5μmol·L-1; the activity of APX in roots was observed raised compared with controls, but APX of leaves was not significantly changed; POD in leaves increased but in roots remained almost unmodified; GPX in roots was not significantly altered, but in leaves induced markedly increase with Cd levels in the medium; upon exposure to 5μmol·L-1 and 25μmol·L-1 Cd, GST prominently increased in roots and leaves. These results suggested that cell membranes in roots and leaves had considerably stability, and changed activity of antioxidative enzymes in Cd-treated had antioxidative function in Salix matsudana to cadmium stress.3. Willows have been shown to be suited for phytoextaction of cadmium, which is depend on large biomass, Cd is phototoxic to plants, Cd depresses photosynthesis, effects plants productivity, reduces phytoextraction rate of Cd. Salix matsudana was hydroponic culture for 14d with CdCl2 (0, 5, 25, 50μmol·L-1), Chlorophyll, Rubisco, PEPC, free amino acid and endopetidase were analyzed. Total Chlorophyll, Chlorophyll a and Chlorophyll b were decreased in Cd-treated plant, Rubisco activity reduced with Cd concentration in the medium, Cd decreased PEPC activity in roots and leaves,Free amino acids of roots remained no change, but free amino acids of leaves increased depending on Cd concentration; endopeptidase of roots were hindered at different dose of Cd, endopetidase of leaves increased at higher dose of Cd. The result showed that photosynthesis of Salix matsudana was disturbed under Cd stress.4. Cd toxicity is associated with growth inhibition and imbalances in many macro- and micronutrient levels. Effect on uptake of mineral nutrient in S. matsudana under cadmium stress was studied at four Cd levels (0, 5, 25, 50μmol·L-1) for 14d. K content of roots remained no change in Cd-treated plant, Except that only at 5μmol·L-1 Cd-treated plant K content of leaves was increased, no significant effect on K content of leaves was found at 2550μmol·L-1 Cd. P uptake in roots was inhibited at all Cd levels, at 2550μmol·L-1 Cd treatment decreased P content in leaves. Ammonium content of roots was elevated, but of leaves was decreased. Nitrate Content of roots and leaves showed a slight increase compared with the control. Only at lowest level (5μmol·L-1) Cd NR activity of roots was increased, NR activity of roots didn't change at 2550μmol·L-1, compared to the control, NR activity of leaves was reduced in all Cd levels. These results suggested that the possibility to improve nutrient enhance to phytoextract Cd in willows.5. Willows have been shown to be promising for Cd phytoextraction, which requires tolerance to Cd stress, the ascorbate-glutathione cycle has been shown to be of great importance in Cd stress, an operation of ascorbate-glutathione cycle enzymes was investigated in roots and leaves of Salix matsudana grown on hydroponics containing 0, 5, 25μmol·L-1 CdCl2 for 28d. AsA content of roots decreased but AsA in leaves increased with increase in Cd level, DHA content of roots increased at 5μmol·L-1 Cd, however, DHA content of leaves decreased at 25μmol·L-1 Cd, significant enhancement of AsA /DHA ratio in roots and leaves was observed at 25μmol·L-1. GSH content of roots and leaves was increased at 5μmol·L-1 Cd, 25μmol·L-1Cd inhibited GSH of roots, GSSG content decreased in roots and leaves compared to control, but at 25μmol·L-1 the ratios of GSH to GSSG was higher in roots and leaves as compared to the control. APX increased in leaves but didn't change significantly in roots respect to the controls, MDHAR of roots was elevated at 5μmol·L-1, and MDHAR of leaves was markedly increased at all concentrations of Cd, DHAR in roots and leaves significantly increased compared with the controls, The results suggested that the ability of Salix matsudana to regulate the enzyme antioxidant system during different conditions might be an important attribute linked to cadmium tolerance.6. The subcellular distribution and chemical of cadmium in Salix matsudana grown in nutrient solution containing 10 and 30μmol·L-1 were investigated. Increased Cd levels in the medium caused a significant increase of Cd concentration in all fractions of leaves and roots, most of the accumulated Cd was isolated to the cell wall of leaves (6569%),high Cd levels were also found in the crude chloroplastic fraction (1422%), the cytosolic fraction accumulated 6.87.7% of Cd, the fraction containing the lowest level of Cd was the organelle fraction. The largest proportion of Cd was located in the walls of roots (5966%),about 1425% of the total Cd contained in the root cell were accumulated in the soluble fraction, Cd concentration of the fractions of roots decreased in the order: FI (cell walls)>FIV (soluble)>FII (trophoplast)>FIII (organelles). The Cd concentrantion was bound to the different chemical forms, chemical forms of Cd (>30%) were extracted with 0.6 mol·L-1 HCl and 1 mol·L-1 NaCl, The leaves and roots, the greatest amount of Cd was found in extraction solution of 0.6 mol·L-1 HCl and 1 mol·L-1 NaCl, followed by 2% HAC, and lowest in extraction of 80% ethanol or d H2O. There was a distinct difference among clones in Cd concentration in subcellular and chemical forms. These results would suggest that Salix matsudana has metabolic mechanism related to cadmium detoxification and tolerance.7. Willows were suitable for Cd and Zn in phytoextraction, contamination contained multiple heavy metals rather than simple. Salix matsudana were grown 30 days in nutrient solution at two concentrations of cadmium (0, 5, 10 and 25μmol·L-1) and zinc (0, 25 and 50μmol·L-1) singly and in factorial combination, Effects of Cd?Zn interactions on metals accumulation and distribution were investigated. Cd uptake was inhibited by Zn and Zn uptake was inhibited by Cd in roots, the results revealed a competitive interaction between Cd and Zn in roots; Zn accumulation was hindered by Cd in shoots, influence of Zn on Cd contents in shoots were dependent on concentrations of those metals in the medium. Cd-Zn interactions altered their accumulation and distribution in shoots and roots, these changes were related to Cd and Zn level in the medium, cadmium and zinc concentrated mainly in the roots. At Cd-Zn interactions, Cd, Zn single or combination disturbed Mn, Cu, Fe, Mg and Ca contents in shoots and roots; K was not significantly altered in treatments. The results showed interactions of Zn and Cd affected those metals uptake and distribution in shoots and roots of S. matsudana.8. Low molecular weight thiol-containing compounds have been reported to play an important role in metal detoxification and accumulation in some higher plants. Relationships between detoxification response to Cd and low molecular weight thiols in S. matsudana were investigated exposed to Cd (5, 25, 50, 100μmol·L-1) for 14d. At 25μmol·L-1 Cys content increased significantly, Cys content of leaves didn't significantly changed. The concentration of NPTs, PTs and TTs showed a very strong increase with Cd level in the mediums. Only 50μmol·L-1γ-GCS activity of leaves was markedly elevated compared to the control,γ-GCS of roots was reduced. These results showed that low macular weight thiols contributed to detoxification in S. matsudana, but didn't depend on GSH biosynthesis.
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