小麦对纳米银的吸收及毒性响应

The uptake and toxicity of silver nanoparticles to wheat

以纳米银(Ag NPs)为研究对象,Ag^+(Ag NO_3)为对照,通过添加半胱氨酸(L-cysteine)探讨小麦对Ag NPs的吸收累积和毒性响应.小麦幼苗于不同浓度的Ag NPs悬浮液中培养4h后,根系出现氧化应激反应和细胞膜损伤,丙二醛(MDA)和过氧化氢酶(CAT)含量分别由对照组的(2.9±0.5)nmol/L/mgprot和(8.6±1.2)U/mgprot增加至(4.9±1.5)nmol/L/mgprot和(12.4±1.2)U/mgprot.半胱氨酸缓解了Ag NO_3对小麦的毒性并使小麦对Ag NO_3的吸收速率常数从(275.4±12.3)L/(kg·h)降低到(210.8±11.2)L/(kg·h).然而,半胱氨酸并没有缓解Ag NPs对小麦的毒性,且Ag NPs的吸收速率常数没有显著性变化[(12.6±0.8)和(11.2±0.6)L/(kg·h)].这说明Ag NPs对小麦的有效性和毒性不仅来源于其释放的Ag^+,还来源于纳米颗粒本身.通过进一步计算Ag NPs暴露液中不同形态Ag的吸收速率常数,发现Ag^+吸收速率常数最高[(275.4±12.3)L/(kg·h)],Ag-cysteine络合物吸收速率常数次之[(210.8±11.2)L/(kg·h)],纳米颗粒吸收速率常数最低[1.6L/(kg·h)].实验中建立了吸收速率常数预测方程,该方程预测结果与实验观测结果一致,说明该方程能够较好地描述小麦吸收Ag NPs的具体过程.

The uptake and toxicity of silver nanoparticles （AgNPs） to wheat were investigated. The wheat seedlings wereexposed to different concentrations of AgNPs suspension in 4h. Oxidative stress and cell membrane damage wereobserved in roots. The content of malondialdehyde （MDA） and catalase （CAT） increased from （2.9±0.5）nmol/L/mgprotand （8.6±1.2）U/mgprot to （4.9±1.5）nmol/L/mgprot and （12.4±1.2）U/mgprot. The addition of L-cysteine reduced thetoxicity of AgNO3 to wheat and decreased the dissolved uptake rate constant of AgNO3 from （275.4±12.3）L/（kg？h） to（210.8±11.2）L/（kg？h）. In contrast, L-cysteine did not affect the toxicity of AgNPs to wheat, and the dissolved uptake rateconstant did not differ significantly before and after the addition of L-cysteine [i.e., （12.6±0.8） vs （11.2±0.6）L/（kg？h）]. Theresults suggested that not only the released Ag＋ from AgNPs, but also the particles themselves contributed to thebioavailability and toxicity of AgNPs. Furthermore, the dissolved uptake rate constants from different species of Ag in thepresence of L-cysteine （i.e., dissolved Ag＋, AgNP particles, and Ag-cysteine） were calculated, and dissolved Ag＋ exhibitedthe highest bioavailability [（275.4±12.3）L/（kg·h）], followed by Ag-cysteine complex [（210.8±11.2）L/（kg·h）] and finallythe nanoparticles [1.6L/（kg·h）]. A model described the uptake process of AgNPs were thus established. The predictedoverall uptake rate constants were comparable to that observed in the experiment, which validated the success of themodel in describing the uptake of AgNPs.