The Mechanism Of EDTA And NTA On The Accumulation And Translocation Of Cadmium In Ramie

Cadmium (Cd) is a major anthropogenic pollutant derived from agricultural andindustrial practices, wastewater irrigations, and smelter wastes and residues from themining and smelting of metalliferous ores. Due to its non-degradability, chemicalmobility and high toxicity to biota, Cd can transfer through food chains and thencause various diseases to plants, animals and even human beings. Given that Cdcontamination has posed an unprecedented threat to a wide range of ecosystem andhuman health, more and more attention has been globally focused on the mechanismsof Cd contamination and remediation technologies.Chelant-enhanced phytoextraction has often been described as a low-cost, safe,environmental-friendily and promosing technique to remediate contaminated soil,which revolutionized phytoextraction technology by utilizing chelating agents toactivate soil heavy metals，enhance the accumulation and translocation in plant andthen facilitate the phytoremediation efficiency. Boehmeria nivea L. Gaudich (ramie),namely “Chinese grass”, is one of the best plant fibers for textile in China. Ramie hasbeen identified as with high biomass and fast growth rate a Cd-tolerant species withlarge biomass and fast growth rate.Therefore, ramie, as an important economic crop inour country, is an ideal crop for Cd pollution control.In this study, we selected ramie as goal plant, Cd as goal contaminant andnon-biodegradable EDTA and biodegradable NTA as soil additives, aiming toinvestigat the effects of non-biodegradable EDTA and biodegradable NTA on soil Cdsolubility, Cd phytotoxicity in microcystis aeruginosa and ramie, and Cdaccumulation in different ramie tissues. To further study the accumulation andtranslocation mechanisms of Cd at subcellular level, we also determined thedistribution of Cd in the extra-and intra-cellular compartments and the cytoderm oframie roots, stems and leaves after the addition of EDTA or NTA. The main contentand conclusions are as follows:Under Cd stress combined chelant, the optical density (OD) and chlorophyll ofthe medium of microcystis aeruginosa kept a similar variation trend with time. UnderEDTA and NTA treatment, the OD and chlorophyll content of the medium increasedwith time, but under EDTA-Cd and NTA-Cd treatment, a downtrend appeared in thelater days. The results revealed that Cd dominated the factor to improve growth ofmicrocystis aeruginosa. Besides, EDTA and NTA had little effect on the growth andmetabolism of microcystis aeruginosa and even exerted alleviation on the damage of Cd to microcystis aeruginosa.The addition of chelant resulted in an increase of MDA contentwith concurrentdecrease of chlorophyll and proline in ramie leaves, which is partially attributed tothat the accumulation of chelant and Cd-chelate complexes in ramie leaves plays animportant role in disturbing the lipoxygenase pathway and photosynthetic process,simultaneously alleviating the damage in the osmosis system of ramie. However,because of the properties of hypotoxicity and biodegradability, NTA has a lessphytotoxic effect on ramie physiology than EDTA, as was evidenced by the higherchlorophyll content and lower MDA content in the NTA group. EDTA addition leadedto an increase in soil urease and a decrease in catalase but had little effect onphosphatase, indicating that EDTA alleviated the damage of Cd on urease butaggravated that on catalase. NTA addition resulted in the increase of all the soilenzymes, manifesting that NTA posed a positive effect on soil enzyme system.EDTA and NTA has a capability to activate soil Cd, as evidenced by that soilEDTA-and NTA-extractable Cd concentrations were remarkably higher than thecontrol. Cd uptake by the root of ramie followed Michaelis–Menten kinetics,indicating that Cd uptake was a transporter-mediated process and gradually saturated.EDTA and NTA could enhance the bioavailability of soil Cd by chelating with themto form Cd-chelate complexes, and then improve the capability of ramie to take upand translocate Cd or Cd-chelate complexes from soil to the aboveground tissues.Pot experiment was designed to systematically investigate the Cd accumulationand subcellular compartmentation in different ramie tissues. Results showed that Cdin each tissue together with Cd translocation factor (TF) after EDTA and NTAaddition were significantly increased with elevated chelant concentration. In spite ofthe decreased cytoderm Cd contents in different tissues, extracellular and intracellularCd content were increased dramatically under chelant treatment, particularly in ramieleaves with EDTA addition. These results revealed that EDTA and NTA couldfacilitate apoplastic and symplastic transport of Cd from root to the abovegroundtissues and improve leaf Cd accumulation because of the extracellular loading amongspongy tissues and intracellular sequestration in mesophyll vacuoles. This studycontributes to the control of Cd accumulation by plants.