基于SRXRF和XANES研究Pb对玉米种子萌芽的影响及其分布和形态特征

以受不同浓度Pb胁迫下的玉米种子萌芽试验为基础,结合SRXRF研究Pb对玉米种子萌芽的影响和Pb在玉米种子的微区分布特征,利用X射线吸收近边结构技术(XANES)对萌芽玉米种子不同部位中Pb的化学形态进行分析,藉以了解种子对Pb的吸收和转化规律。结果表明,玉米种子的发芽率、根芽伸长量随培养溶液中Pb(NO3)2浓度增加而降低。种子发芽率、平均芽长、平均根长与暴露Pb浓度间的方差分析P-value分别为2.0×10!3,1.4×10!4和2.39×10!8,均小于0.01,为极显著差异,说明Pb胁迫对种子萌芽和根芽生长造成了极显著影响,且对根长抑制作用更大。SRXRF分析结果表明,种皮和胚结构是玉米种子富集Pb的主要部位,Pb富集在胚结构中将抑制种子萌芽。各种子样品的Pb-LⅢ(13035 eV)边XANES谱图相同,为同一种Pb形态,拟合结果显示其含74.3%的氯化磷酸铅和24.2%硬脂酸铅,说明Pb主要以氯化磷酸铅的形式沉积于玉米体内,并有少部分以与羧基结合的有机铅形式存在。

A Study on Distribution and Chemical Speciation of Lead in Corn Seed Germination by Synchrotron Radiation X-ray Fluorescence and Absorption near Edge Structure Spectrometry

Synchrotron radiation X-ray fluorescence analysis technology (SRXRF) can effectively reduce the detection limit for the determination of heavy metal elements. The technique is especially suitable for in situ nondestructive analysis of biological samples with low contents. By corn seed germination test, and combining with SRXRF technique, the effects of Pb on corn seed germination and Pb micro-distribution in the corn seed were studied. X-ray absorption near edge structure (XANES) technique was also used to analyze the Pb chemical speciation in different parts of corn seed. The above experiments were carried out for understanding the absorption and transformation mechanism of Pb by corn seeds. The results showed that the germination rate, bud length and root length decreased with the increasing contents of Pb. The analysis of variance showed that P-value of the germination rate, bud length and root elongation of corn seeds which were exposed to different concentration of Pb were 2.0 × 10⁻³, 1.4 × 10⁻⁴ and 2.4 × 10⁻⁸ respectively, suggesting there were highly significant differences during this three indicators and the content of Pb. In addition, the inhibition effect on root growth was greater. The results of SRXRF analysis showed that Pb was mainly enriched in episperm and embryo, which would inhibit embryonic develop into bud and root. Moreover, the results showed that all samples including root, shoot and the different part of seed had the same Pb-L_III (13035 eV) XANES spectra and Pb speciation. The linear combination fitting results indicated that the lead phosphate chloride and lead stearate accounted for 74.3% and 24.2% respectively, suggesting that the main Pb speciation in corn was lead phosphate chloride which deposited inside of corn, and a few combined with carboxylic to form organic lead.