Mishra Seema, Alfeld Matthias, Sobotka Roman, Andresen Elisa, Falkenberg Gerald, Küpper Hendrik
CSIR-National Botanical Research Institute, Plant Ecology & Environmental Science Division, Rana Pratap Marg, Lucknow 226 001 (U.P.), India Universität Konstanz, Mathematisch-Naturwissenschaftliche Sektion, Fachbereich Biologie, Postfach M665, D-78457 Konstanz, Germany
Deutsches Elektronen-Synchrotron (DESY), Photon Science, Notkestr. 85, 22603 Hamburg, Germany.
J Exp Bot. 2016 Aug;67(15):4639-46. doi: 10.1093/jxb/erw238. Epub 2016 Jun 23.
Arsenic (As) pollution is a serious concern worldwide. Recent studies under environmentally relevant conditions revealed that, in the aquatic plant Ceratophyllum demersum, pigments are the first observable target of toxicity, prior to any effect on photosynthetic parameters or to oxidative stress. Lethal toxicity was initiated by a change of As species and their distribution pattern in various tissues. Here, the localization of As was investigated at the subcellular level through X-ray fluorescence using a submicron beam and a Maia detector. Further, it was possible to obtain useful tissue structural information from the ratio of the tomogram of photon flux behind the sample to the tomogram of Compton scattering. The micro-X-ray fluorescence tomograms showed that As predominantly accumulated in the nucleus of the epidermal cells in young mature leaves exposed to sublethal 1 µM As. This suggests that As may exert toxic effects in the nucleus, for example, by interfering with nucleic acid synthesis by replacing phosphorous with As. At higher cellular concentrations, As was mainly stored in the vacuole, particularly in mature leaves. An analysis of precursors of chlorophyll and degradation metabolites revealed that the observed decrease in chlorophyll concentration was associated with hindered biosynthesis, and was not due to degradation. Coproporphyrinogen III could not be detected after exposure to only 0.5 µM As. Levels of subsequent precursors, for example, protoporphyrin IX, Mg-protoporphyrin, Mg-protoporphyrin methyl ester, and divinyl protochlorophyllide, were significantly decreased at this concentration as well, indicating that the pathway was blocked upstream of tetrapyrrole synthesis.
砷（As）污染是全球范围内严重关注的问题。最近在环境相关条件下进行的研究表明，在水生植物金鱼藻中，色素是毒性的首个可观察到的靶点，早于对光合参数或氧化应激产生任何影响之前。致死毒性是由砷形态及其在各种组织中的分布模式变化引发的。在此，通过使用亚微米束和Maia探测器的X射线荧光在亚细胞水平研究了砷的定位。此外，从样品后方光子通量的断层图像与康普顿散射的断层图像的比率中可以获得有用的组织结构信息。微X射线荧光断层图像显示，在暴露于亚致死浓度1 μM砷的幼嫩成熟叶片中，砷主要积累在表皮细胞的细胞核中。这表明砷可能在细胞核中发挥毒性作用，例如，通过用砷取代磷来干扰核酸合成。在较高细胞浓度下，砷主要储存在液泡中，尤其是在成熟叶片中。对叶绿素前体和降解代谢物的分析表明，观察到的叶绿素浓度降低与生物合成受阻有关，而不是由于降解。仅暴露于0.5 μM砷后就无法检测到粪卟啉原III。在此浓度下，后续前体，例如原卟啉IX、镁原卟啉、镁原卟啉甲酯和二乙烯基原叶绿素酸酯的水平也显著降低，表明该途径在四吡咯合成的上游被阻断。
