Comparisons in subcellular and biochemical behaviors of cadmium between Iow-Cd and high-Cd accumulation cultivars of pakchoi （Brassica chinensis L.）

Subcellular distributions and chemical forms of cadmium （Cd） in the leaves, stems and roots were investigated in low-Cd accumulation cultivars and high-Cd accumulation cultivars ofpakchoi （Brassica chinensis L.）. Root cell wall played a key role in limiting soil Cd from entering the protoplast, especially in the low-Cd cultivars. The high-Cd cultivars had significantly higher leaf and stem Cd concentrations than the low-Cd cultivars in cell wall fraction, chloroplast/trophoplast fraction, organelle fraction and soluble fraction. In low-Cd cultivars, which were more sensitive and thus had greater physiological needs of Cd detoxification than high-Cd cultivars, leaf vacuole sequestrated higher proportions of Cd. Cd in the form of pectate/protein complexes （extracted by 1 tool. L~ NaC1） played a decisive role in Cd translocation from root to shoot, which might be one of the mechanisms that led to the differences in shoot Cd accumulation between the two types of cultivars. Furthermore, the formation of Cd- phosphate complexes （extracted by 2% HAc） was also involved in Cd detoxification within the roots of pakchoi under high Cd stress, suggesting that the mechanisms of Cd detoxification might be different between low- and high-Cd cultivars.     

PS和ZnONPs颗粒生态冠复合物的赋存状态及形成规律

水环境中的生物大分子会在水中残留的颗粒物表面形成生态冠,从而影响颗粒物的赋存状态和生态行为.本研究测定了纳米氧化锌（ZnONPs）和聚苯乙烯微塑料（PS）与斑马鱼体外生物大分子作用形成的生态冠复合物的形貌、组分、水动力学直径及Zeta电位等,以此探究微、纳米颗粒生态冠复合物的赋存状态与形成规律.结果表明,斑马鱼体外生物大分子主要含有类酪氨酸蛋白、类色氨酸蛋白、类富里酸、可溶解性生物副产物和类腐殖酸.扫描电镜观察发现,PS和ZnONPs表面部分或全部被生物大分子包裹,形成生态冠复合物.三维荧光光谱分析 发现,PS和ZnONPs对各类生物大分子亲和力不同.随着作用时间延长（3~24 h）,在PS生态冠组分中类酪氨酸蛋白的占比逐渐增加,类腐殖酸的占比逐渐减少;ZnONPs生态冠中这两类生物大分子组分的变化趋势呈相反的变化趋势;这两种生态冠复合物的组分变化都呈现时间-效应关系.PS-生态冠复合物和ZnONPs-生态冠复合物的水动力学直径都随着作用时间延长而增加.然而这两种生态冠复合物的Zeta电位绝对值却呈现不同的时间-效应关系,PS-生态冠复合物的Zeta电位绝对值随着作用时间延长而增加,ZnONPs-生态冠复合物的Zeta电位绝对值随着 作用时间延长而减小.上述结果表明,微、纳米颗粒在水体中的赋存状态与其所处生物环境、生态冠组分、表面电荷、水动力学直径等具有密切相关性,这为进一步研究微、纳米颗粒物在水体中的生态效应提供了重要的研究思路和科学依据.