柠檬酸对纳米氧化铁诱导水稻根表铁膜形成及对水稻铁吸收转运的影响

The effect of citric acid on iron plaque formation on root surface and iron uptake/translocation in rice after γFe_2O_3 NPs exposure

本研究利用水培模拟实验探讨了柠檬酸对纳米氧化铁(NPs,γFe_2O_3)诱导水稻根表铁膜的影响,同时研究了其对铁(Fe)在植株体内吸收转运的影响。结果表明,低浓度柠檬酸包被和未包被处理NPs能够显著增加水稻根生物量,但对水稻地上部生物量影响不显著。NPs能够诱导根表铁膜形成,然而铁膜量随着柠檬酸浓度增加而下降,可能是由于柠檬酸降低NPs的Fe2+释放量造成的;但是2.10 mg·L^(-1)柠檬酸包被NPs能显著提高根表铁膜量。根表铁膜主要以无定型为主(除柠檬酸包被处理外),晶格态仅占铁膜总量的24.88%~48.12%;其中,由于根表铁膜的晶格构造与NPs类似,可能晶格态铁膜主要来源于NPs的直接吸附沉淀。柠檬酸的加入显著降低Fe在根表和根中累积,但是增加了Fe在地上部的累积;然而,柠檬酸包被NPs处理能够增加Fe在根表和植株地上部的累积,但降低Fe在根系中的累积。2.10 mg·L^(-1)柠檬酸(包被和未包被NPs处理)能够减弱Fe从根表向根内的转移,但是增强了Fe从根向地上部的转移。不同NPs处理条件下,Fe在水稻植株不同部位均存在富集现象,根表和地上部的富集系数显著高于根内。

The aim of this study was to identify the effect of citric acid on iron plaque formation on the root surface of rice, and iron uptake and translocation after exposure to γFe203 nanoparticles （NPs） in a hydroponic culture experiment. The results showed that the addition of citric acid （low concentration or uncoated NPs ） greatly increased the biomass of roots, but not to that of aboveground rice, compared with the single Fe203 NPs treatment. Fe203 NPs exposure induced iron plaque formation on root surfaces of rice. However, the presence of citric acid decreased the amount of iron plaque, which could have been caused by low Fe2＋ dissolution from Fe203 NPs in the presence of citric acid. Also, citric acid（ 2.10 mg·L-I） coated NPs promoted iron plaque formation. Iron plaque was mainly comprised of amorphous fractions, ex- cept in the citric acid-coated treatment. The crystal fraction was only 24.88%-48.12% of the total amount of iron plaque. As the crystal fraction was consistent with that of NPs from the XRD analysis, it was speculated that the crystal fraction could come mainly from the direct adsorption precipitation of NPs, and then as iron plaque components. The addition of citric acid significantly decreased iron accumulation on the root surface and in the root, but significantly increased the accumulation in the aboveground parts. However, the citric acid-coated NPs treatment increased the accumulation of iron on the root surface and in the shoot, and decreased the accumulation in the root. Low concen- tration of citric acid（2.10 mg·L-1, coated and uncoated NPs） decreased iron translocation from the root surface to the root, and increased the translocation from the root to aboveground parts. Iron enrichment was found in all NPs treatments, and the enrichment factors on the root surface and in aboveground parts were significantly higher than in the root.