Arsenic distribution and speciation in an arsenic hyperaccumulator fern by X-ray spectrometry utilizing a synchrotron radiation source

Hokura, Akiko; Omuma, Ryoko; Terada, Yasuko; Kitajima, Nobuyuki; Abe, Tomoko; Saito, Hiroyuki; Nakai, Izumi

doi:10.1039/b512792k

Cited by 66 publications

(54 citation statements)

References 17 publications

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“…The m-XRF imaging analysis was carried out at BL37XU of the Super Photon Ring-8 facility in Hyogo, Japan. Details of the m-XRF system have been reported by Kamijo et al (2003) and Hokura et al (2006). Elemental maps were obtained by scanning the samples with a 10.0-keV monochromatized beam.…”

Section: M-xrf Analysismentioning

confidence: 99%

Dynamic Changes in the Distribution of Minerals in Relation to Phytic Acid Accumulation during Rice Seed Development

et al. 2012

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Phytic acid (inositol hexakisphosphate [InsP 6 ]) is the storage compound of phosphorus in seeds. As phytic acid binds strongly to metallic cations, it also acts as a storage compound of metals. To understand the mechanisms underlying metal accumulation and localization in relation to phytic acid storage, we applied synchrotron-based x-ray microfluorescence imaging analysis to characterize the simultaneous subcellular distribution of some mineral elements (phosphorus, calcium, potassium, iron, zinc, and copper) in immature and mature rice (Oryza sativa) seeds. This fine-imaging method can reveal whether these elements colocalize. We also determined their accumulation patterns and the changes in phosphate and InsP 6 contents during seed development. While the InsP 6 content in the outer parts of seeds rapidly increased during seed development, the phosphate contents of both the outer and inner parts of seeds remained low. Phosphorus, calcium, potassium, and iron were most abundant in the aleurone layer, and they colocalized throughout seed development. Zinc was broadly distributed from the aleurone layer to the inner endosperm. Copper localized outside the aleurone layer and did not colocalize with phosphorus. From these results, we suggest that phosphorus translocated from source organs was immediately converted to InsP 6 and accumulated in aleurone layer cells and that calcium, potassium, and iron accumulated as phytic acid salt (phytate) in the aleurone layer, whereas zinc bound loosely to InsP 6 and accumulated not only in phytate but also in another storage form. Copper accumulated in the endosperm and may exhibit a storage form other than phytate.

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Section: M-xrf Analysismentioning

confidence: 99%

Dynamic Changes in the Distribution of Minerals in Relation to Phytic Acid Accumulation during Rice Seed Development

et al. 2012

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“…When grown in areas with elevated levels of arsenic, more than 1% of the dry weight of a P. vittata frond is arsenic (Tongbin et al, 2002;Wang et al, 2002). Previous studies have shown that this plant efficiently takes up arsenate As(V) from the soil and rapidly transports it to the shoot in the xylem mainly as As(V) (Kertulis et al, 2005), where it arrives in the petiole and midrib of the frond as arsenate (Hokura et al, 2006) and is finally stored in the fronds as free arsenite As(III), as determined by x-ray absorption spectroscopy (XAS; Lombi et al, 2002;Webb et al, 2003;Ze-Chun et al, 2004) and highpressure liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS; Wang et al, 2002;Zhao et al, 2003). Such a model suggests that arsenate in the frond is reduced to arsenite for storage.…”

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A Novel Arsenate Reductase from the Arsenic Hyperaccumulating Fern Pteris vittata

et al. 2006

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Pteris vittata sporophytes hyperaccumulate arsenic to 1% to 2% of their dry weight. Like the sporophyte, the gametophyte was found to reduce arsenate [As(V)] to arsenite [As(III)] and store arsenic as free As(III). Here, we report the isolation of an arsenate reductase gene (PvACR2) from gametophytes that can suppress the arsenate sensitivity and arsenic hyperaccumulation phenotypes of yeast (Saccharomyces cerevisiae) lacking the arsenate reductase gene ScACR2. Recombinant PvACR2 protein has in vitro arsenate reductase activity similar to ScACR2. While PvACR2 and ScACR2 have sequence similarities to the CDC25 protein tyrosine phosphatases, they lack phosphatase activity. In contrast, Arath;CDC25, an Arabidopsis (Arabidopsis thaliana) homolog of PvACR2 was found to have both arsenate reductase and phosphatase activities. To our knowledge, PvACR2 is the first reported plant arsenate reductase that lacks phosphatase activity. CDC25 protein tyrosine phosphatases and arsenate reductases have a conserved HCX 5 R motif that defines the active site. PvACR2 is unique in that the arginine of this motif, previously shown to be essential for phosphatase and reductase activity, is replaced with a serine. Steady-state levels of PvACR2 expression in gametophytes were found to be similar in the absence and presence of arsenate, while total arsenate reductase activity in P. vittata gametophytes was found to be constitutive and unaffected by arsenate, consistent with other known metal hyperaccumulation mechanisms in plants. The unusual active site of PvACR2 and the arsenate reductase activities of cell-free extracts correlate with the ability of P. vittata to hyperaccumulate arsenite, suggesting that PvACR2 may play an important role in this process.

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“…Several authors have examined the distribution of As within fronds of the hyperaccumulator Pteris vittata and found that the majority of As accumulates in the pinnae (Lombi et al, 2002;Hokura et al, 2006;Pickering et al, 2006). However, with the exception of As distribution in rice grains (Meharg et al, 2008;Lombi et al, 2009;Carey et al, 2011), there is surprisingly little information available regarding the cellular or subcellular distribution of As in other plant tissues, especially in nonhyperaccumulators (including agronomic species; Zhao et al, 2009).…”

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Examination of the Distribution of Arsenic in Hydrated and Fresh Cowpea Roots Using Two- and Three-Dimensional Techniques

et al. 2012

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Arsenic (As) is considered to be the environmental contaminant of greatest concern due to its potential accumulation in the food chain and in humans. Using novel synchrotron-based x-ray fluorescence techniques (including sequential computed tomography), short-term solution culture studies were used to examine the spatial distribution of As in hydrated and fresh roots of cowpea (Vigna unguiculata 'Red Caloona') seedlings exposed to 4 or 20 mm arsenate [As(V)] or 4 or 20 mm arsenite. For plants exposed to As(V), the highest concentrations were observed internally at the root apex (meristem), with As also accumulating in the root border cells and at the endodermis. When exposed to arsenite, the endodermis was again a site of accumulation, although no As was observed in border cells. For As(V), subsequent transfer of seedlings to an As-free solution resulted in a decrease in tissue As concentrations, but growth did not improve. These data suggest that, under our experimental conditions, the accumulation of As causes permanent damage to the meristem. In addition, we suggest that root border cells possibly contribute to the plant's ability to tolerate excess As(V) by accumulating high levels of As and limiting its movement into the root.

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Arsenic distribution and speciation in an arsenic hyperaccumulator fern by X-ray spectrometry utilizing a synchrotron radiation source

Cited by 66 publications

References 17 publications

Dynamic Changes in the Distribution of Minerals in Relation to Phytic Acid Accumulation during Rice Seed Development

Dynamic Changes in the Distribution of Minerals in Relation to Phytic Acid Accumulation during Rice Seed Development

A Novel Arsenate Reductase from the Arsenic Hyperaccumulating Fern Pteris vittata

Examination of the Distribution of Arsenic in Hydrated and Fresh Cowpea Roots Using Two- and Three-Dimensional Techniques

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