三角褐指藻对镉的富集机制和转化途径

Bioaccumulation and transformation of cadmium by Phaeodactylum tricornutum

本论文报道了在典型配体乙二胺四乙酸(EDTA)和半胱氨酸(Cys)的存在下三角褐指藻(Phaeodactylum tricornutum)对镉(Cd)的富集机制和转化途径.毒性试验表明,两种配体均可有效降低Cd对三角褐指藻的毒性.ICP-MS分析结果表明,EDTA存在下细胞表面吸附和内部吸收Cd的量随着培养液中EDTA浓度的升高(自由Cd2+浓度的降低)而降低,基本符合自由离子活度模型(Free ion activity model,FIAM)的预测;而Cys存在时,细胞表面吸附Cd的量随着Cys浓度的增大呈现先增加后降低的趋势.在Cys浓度由空白浓度增加至4.45μmol/L时,细胞内部吸收Cd的量呈现增加趋势;而大于4.45μmol/L时,又趋于同一水平的现象,结果偏离FIAM.FTIR和XPS研究确证了细胞壁上的-OH和-NH2基团对Cd的吸附起主要作用.Cd胁迫后P.tricornutum细胞内诱导合成的植物螯合肽(PCs)的HPLC和ESI-IT-MS分析结果证实造成这两种配体对P.tricornutum积累和转化Cd行为产生不同影响的主要原因是Cys作为Cd2+的配体的同时,又是P.tricornutum细胞内PCs合成的前驱体之一.P.tricornutum细胞内PCs、氧化型PCs以及Cd-PC2的发现证明了Cd诱导P.tricornutum合成的PCs反过来钝化细胞内吸收的Cd,降低了其对P.tricornutum细胞的氧化毒性.

This study reported the bioaccumulafion and transformation of cadmium （Cd） by Phaeodactylum tricornutum in the presence of ethylenediamine tetra acetic acid （EDTA） and cysteine （Cys）. Both EDTA and Cys can alleviate the toxicity of Cd to P. tricornutum. Short term intracellular uptake and extracellular adsorption experiments using ICP-MS indicated that the amounts of Cd accumulated on the cell surface of P. tricornutum and inside the cell decreased along with the increase of EDTA concentration, which conformed to the prediction of the Free Ion Activity Model （FIAM）. However, extracellular adsorption of Cd increased at first and then decreased along with the increase in the concentration of Cys, while intracellular uptake increased under Cys concentrations from the blank value to 4.45 pmol/L, and then tended to remain at the same level when the Cys concentration was greater than 4.45 ~tmol/L, and this deviated remarkably from the FIAM. The interactions of Cd with -Si-OH, -C-OH and NH2（CO）-OH on the cell wall were confirmed using FT-IR and XPS studies. The results obtained using HPLC of the phytochelatins （PCs） produced by P. tricornutum under CdC12, Cd-EDTA and Cd-Cys stress suggested that the main reason for the different effects of EDTA and Cys on the bioaccumulation and transformation of Cd by P. tricornutum was that Cys is not only a complexing ligand to Cd, as is EDTA, but also it is a precursor of the intracellular synthesizing PCs participating in the cellular defense mechanism against Cd. Furthermore, the discovery of in vivo PCs and oxidized-PCs as well as Cd-PC2 in P. tricornutum using ESI-IT-MS provided the evidence for deactivation of Cd by the PCs, reducing Cd-toxicity to P. tricornutum.