| Cadmium (Cd) pollution resulted from industrial production such as smelting,agricultural activities such as irrigation, fertilization, and atmosphericsedimentation, which has aroused public concern and become the key of miningarea remediation and food security. Cd with high toxicity, carcinogenesis andteratogenesis, existed persistently in soil and water and was ea sy to accumulate inorganism. It not only caused great damage to the ecological system, but also posedenormous threat to food security concerning about human life and health throughfood chain. Approximately1/5(about20million hectares) of farmland wascontaminated by heavy metals in China, involved in an area of13300hectares,11provinces and25regions. Therefore, the remediation of Cd contaminated sites isthe significant measure referring to the safety and efficiency of soil production, aswell as the sustainable development of ecological restoration.Phytoremediation is a novel, economical and green remediation technology.Boehmeria nivea (L.) Gaud.(ramie) grows fast with great biomass in most areasand has strong adaptability, high economic valu e, as well as certain endurance toCd. It also show strong tolerance to drought and barren, which makes it a goodcandidate for repairmen of mining area, and potential to apply in remediating Cdpollution, the ecological restoration of abandoned lands. Whe n exposed to heavymetal, plant will automatically induce a series of responses, includingmorphological, physiological and molecular alteration. The present study is basedon plant physiology, ecotoxicology and plant tolerance mechanism, using ramieand Cd as research object. After screening Cd tolerance varieties, Cd simulationexperiment, exogenous citric and oxalic acid treatment, Cd measurement andphysiological analysis were conducted by atomic absorption spectrophotometer,UV spectrophotometer, enzyme analysis instruments etc. The objectives of thisstudy were to (i) explore the potential of ramie in phytoextraction andtranslocation capability of Cd;(ii) determine the effects of different Cd levels onplant growth, relative water content, root activity, photosynthesis, membraneoxidation, protein synthesis and antioxidant enzymes;(iii) compare the effects ofdifferent concentrations of exogenous citric and oxalic acid in regulating thephysiological system involved in stress endurance. For the better application and high efficiency of ramie in Cd polluted farmland and mining area remediation, thisstudy is significant in view of basic points.The main results and discussion are as follows:Under hydroponic condition, most heavy metal tended to accumu late in plantroots and its content is about9-10times of that in aerial part. With the increasingof Cd stress, the uptake of Cd in ramie root and translocation factor also improved.Cd content ranged from268.0to374.4in root and25.2to41.2mg kg–1DW inshoot, respectively. The effect of low concentration of citric acid (1.5mM) exertedbetter effect on Cd accumulation and transport, and significantly facilitated Cduptake by27%in root and by1-fold in shoot, respectively. And translocationefficiency was increased by62%. The Cd translocation efficiency from root toshoot was improved by maximum66%under3mM of oxalic acid.Cd adversity stress resulted in the decrease of plant biomass and root activity, theinhibition of chlorophyll and soluble protein synthesis, the enlargement ofmembrane lipid peroxidation and the various changes of antioxidant enzymes,which caused injury to plant tissues. Compared to the various changes of controlgroup, two levels of citric and oxalic acid treatment allev iated the metal toxicityand damage, as seen from the increase in plant biomass, relative water content,root activity, photosynthetic pigments, protein content and antioxidant enzymesactivities, and the alleviation of membrane lipid peroxidation in root and shoot.The low level of citric acid (1.5mM) was more sensitive than the other groups,which caused a series of physiological changes in plants under cadmium toxic ityand played an important role. Exogenous citric and oxalic acid promote d theuptake and transport of Cd by plants, and alleviated the oxidative damage byforming chelate with heavy metal. Citric acid exhibited more prominent mitigatingeffect than oxalic acid due to its stronger ligand affinity for chelating with metaland avoiding the toxicity injury of free Cd ions more efficiently. Th is studyprovides a potential strategy for efficient Cd remediation with ramie.In conclusion, the results showed that exogenous citric and oxalic acid chelat ingwith Cd not only increase the mobility of Cd and promote Cd accumulation inplant, but also can ease the toxicity of free Cd ions. |
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