| The 11 species tropical coastal plants of Paspalum vaginatum Sw.,Gynura divaricata(L.)DC.,Ischaemum aristatum L.,Lepturus repens(G.Forst.)R.Br.,Cynodondactylon(Linn.)Pers,Fuirena ciliaris(Linn.)Roxb,Sesuvium portulacastrum(L.)L.,Portzulaca oleracea L.,Cenchrus echinatus L.,Gynura formosana Kitam and Sporobolus virginicus(L.)Kunth were used to treat with Cd.The results found that four species of them showed higher Cd tolerance,P.oleracea,P.vaginatum,I.aristatum and G.formosana Kitam.The further researches were focused on the P.vaginatum and G.formosana Kitam to preliminary identify the mechanisms of plant tolerance to Cd,from physiological and biochemical influences of Cd to plant growth,nutrient(N,P,K)absorption,root activity,chlorophyll content,membrane permeability,membrane lipid peroxidation,osmotic adjustment substance and protective enzyme system.The results were as follows:1.Evaluation the tolerance to Cd of 11 species of tropical coastal plants in pot.The results showed that G.formosana Kitam,I.aristatum L.,P.oleracea L.and P.vaginatum Sw.had strong tolerance to Cd,Their root growth,height,biomass did not significantly decreased(p<0.05)after treatment in cadmium;The roots of P.oleracea L.and P.vaginatum Sw.could accumulated Cd,which was up 839.55 mg/kg and 1144.64 mg/kg,respectively.G.formosana Kitam and I.aristatum L.could accumulate Cd in both stems and roots,and the accumulation in stems was up to 709.45 mg/kg and 164.20 mg/kg,respecyively Cd,which was higher in stems than in roots.The content is higher than the critical content Cd hyperaccumulators(100 mg/kg).Thus the four species of G.formosana Kitam,I.aristatum L.,P.oleracea L.and P.vaginatum Sw.have a strong Cd accumulation,and could be used as the candidates of Cd hyperaccumulators for repair Cd contaminated soil.2.The researches were investigated the effects of Cd treatment(0-200 mg/kg)on plant growth,root activity,leaf membrane permeability,membrane lipid peroxidation,protective enzyme activity and Cd accumulation by Cd treatment in soil cultured P.vaginatum Sw.and G.formosana Kitam.The results showed that,in P.vaginatum Sw.when the Cd treatment was over 50 mg/kg,the activity of CAT was lower,the synergistic effect of SOD and CAT was reduced,MDA accumulation and root activity were decreased and plant growth inhibition;in G.formosana Kitam,when the Cd treatment was lower than 100 mg/kg,the activity of CAT,POD and MDA was increased as the Cd treated concentration addition,the root activity and plant growth were normal;wherwas when the Cd treatment was over 200 mg/kg,the membranous permeability and peroxidation were significantly increased,the scavenging activity of antioxidant enzyme system was inhibited,the root activity and plant growth were obviously decreased in G.formosana Kitam.3.The researches were investigated the effects of Cd treatment(0-200 mg/kg)on osmotic adjustment substance in P.vaginatum Sw.and G.formosana Kitam.The results showed that the soluble sugar accumulation was increased in roots,stems and leaves of P.vaginatum Sw.as the Cd treated concentration addition when Cd treatment was lower than 200 mg/kg,but the soluble sugar accumulation and the osmotic adjustment ability was significantly reduced in stems and leaves when the Cd treated concentration was 200 mg/kg.The content of proline was lower when Cd treatment was 0-10 mg/kg,while the proline was highly increased at 50 mg/kg Cd,then rapidly decreased.This showed that the soluble sugars play a major role in osmotic adjustment;proline improves osmotic adjustment of P.vaginatum Sw.only in lower Cd stress.In G.formosana Kitam,when the Cd treatment was lower than 100 mg/kg,the soluble sugar accumulation was increased,and the proline content was higher than the control in leaves.This showed that the soluble sugar and proline synergistic regulated osmotic pressure of G.formosana Kitam.4.The researches were investigated the effects of Cd treatment(0-200 mg/kg)on the absorption of nutrients(N,P,K)in P.vaginatum Sw.and G.formosana Kitam.The results showed that absorption amount of N,P,K was reduced as Cd treated concentration addition in P.vaginatum Sw.,which might be the Cd accumulation in roots inhibited the absorption of nutrient elements.In G.formosana Kitam,the absorption amount of N and K was increased at(0-200 mg/kg),then decreased at(0-200 mg/kg),whereas,the P was decreased.The increased absorption of N and K under lower Cd stress might be related to the Cd tolerance of G.formosana Kitam which is higher than P.vaginatum Sw..5.The researches were investigated the effects of Cd treatment(land 50 mg/kg)on the chemical forms of Cd in roots,stems and leaves;and the subcellular distribution of Cd in roots and leaves of P.vaginatum Sw.and G.formosana Kitam.The toxicity,migration ability of total water and ethanol extractable forms of Cd is strongest.The distribution ratio of total water and ethanol extractable forms of Cd were decreased in all organs of P.vaginatum Sw.and G.formosana Kitam.Under 50 mg/kg,the activity,toxicity,migration ability of the chemical forms of FHCl and FHAC were the weakest,FNaCl was in middle.In P.vaginatum Sw.,the chemical forms of FNaCl and FHCl were increased in roots,the chemical form FHAC was increased in stems,and the chemical forms of FHAC and FHCl were increased in leaves under 50 mg/kg,which might related to the stronger enrichment ability of Cd in the roots of P.vaginatum Sw..In G.formosana Kitam,the chemical forms of FHAC in stems and leaves,the chemical forms of FNaCl in roots,stems and leaves were increased under 50 mg/kg,which might be beneficial for Cd transportion from roots to leaves.This might lead to the massive enrichment of Cd in the aboveground parts of G.formosana Kitam.Distribution of Cd in two species plants showed relatively large difference.Compare with P.vaginatum Sw.,sum of Cd in cell wall and soluble fraction in the roots and leaves of G.formosana Kitam was decreased.The cell wall binding and enrichment ability of the soluble fraction in roots of G.formosana Kitam was lower than those of P.vaginatum Sw.,which also might result in the Cd easily transfer to the aboveground of G.formosana Kitam,,while the Cd mainly accumulates in the roots of P.vaginatum Sw..Under 50 mg/kg,the distribution ratio of Cd in cell wall and soluble fraction in the roots of P.vaginatum Sw.was increased by 6.14%and 0.32%respectively;the distribution ratio of Cd in cell wall of leaves was increased by 4.25%,and the distribution ratio of Cd in stronger metabolic chloroplast was increased by 1.92%.The sum of distribution ratio of Cd in cell wall and soluble fraction in the roots of G.formosana Kitam was increased by 16.68%,and 11.47%in leaves,respectively.The distribution ratio of Cd in protoplasts(roots),chloroplasts(leaves)and the cell membranes was decreased in comparison to the 1 mg/kg Cd treatment.This might one reason that the tolerance to Cd of G.formosana Kitam was higher than P.vaginatum Sw..6.The conclude from the above results showed that P.vaginatum Sw.and G.formosana Kitam showed physiological and biochemical responses to Cd toxicity in organs,tissues,cellular levels.And the reduce toxicity of Cd to plants by fixation Cd in cell walls,compartmentation Cd in vacuoles,chemical form changes,antioxidant enzymes,osmotic adjustment of soluble sugar and proline.The plants of P.vaginatum Sw.and G.formosana Kitam have application prospect to recovery the Cd contaminated soil. |
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