Arsenic hyperaccumulator Pteris vittata (PV) is efficient in taking up As and nutrients from As-contaminated soils. We evaluated the mechanisms used by PV to mobilize As and Fe by examining the impacts of As and root exudates on FeAsO4 solubilization, and As and Fe uptake in four plants: As-hyperaccumulators PV and Pteris multifida (PM), nonhyperaccumulator Pteris ensiformis (PE), and angiosperm plant tomato (Solanum lycopersicum). Phytate and oxalate were dominant in fern plants (>93%), which were 50-83, 15-42, and 0-32 mg kg(-1) phytate and 10-15, 7-26, and 4-12 mg kg(-1) oxalate for PV, PM, and PE respectively, with higher As inducing greater phytate exudation and no phytate being detected in tomato exudates. PV treated with phytate+FeAsO4 had higher As and Fe contents and larger biomass than phytate or FeAsO4 treatment, which were 340 vs 20 and 130 mg kg(-1) As in the fronds and 7900 vs 1600 and 4100 mg kg(-1) Fe in the roots. We hypothesized that As-induced phytate exudation helped PV to take up Fe and As from insoluble FeAsO4 and promoted PV growth. Our study suggests that phytate exudation may be special to fern plants, which may play an important role in enhancing As and nutrient uptake by plants, thereby increasing their efficiency in phytoremediation of As-contaminated soils.

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A simple chemical method for the production of single-crystalline alpha-Si(3)N(4) nanobelts has been developed, consisting of nitridation of a high-Si-content Fe-Si 'catalyst' by ammonia at 1300 degrees C. The as-synthesized product was characterized by means of x-ray diffraction, electron microscopy and energy-dispersive x-ray spectroscopy. The alpha-Si(3)N(4) nanobelts have widths of 60-120 nm, thicknesses of 10-30 nm and lengths up to microns. Four intense green-blue luminescence bands at 398 nm (3.12 eV), 434 nm (2.86 eV), 492 nm (2.52 eV) and 540 nm (2.30 eV) were observed and analysed for the product, which indicates the potential applications in optoelectronics. The growth mechanism has also been speculated upon. The potential technological importance of the product, the simplicity of the preparation procedure, as well as the cheap commercial precursor of Fe-Si alloy particles makes this study both scientifically and technologically interesting.

Synthesis and field-emission behavior of highly oriented boron carbonitride nanofibers

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Large-area and uniform quasi-aligned titanium oxide (TiO2) nanowire arrays have been produced in situ on a titanium (Ti) foil by a simple high-temperature oxidation process with acetone as the oxidant. The products are characterized by X-ray diffraction, electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The TiO2 nanowires have a rutile single-crystalline structure. The typical diameters range from 20 to 50 nm and lengths are up to a few micrometers. Since the Ti foil serves as both the source of Ti and substrate, direct synthesis and assembly of TiO2 nanowire arrays on a conductive Ti substrate is accomplished in a single step. Consequently, good intrinsic adhesion and electrical contact are achieved naturally between the nanowires and metal substrate. Such TiO2 nanowire arrays exhibit good field emission properties with a low turn-on field of 4.1 V/microm boding well for applications in vacuum microelectronics.

Arsenic (As) is a toxic carcinogen so it is crucial to decrease As accumulation in crops to reduce its risk to human health. Arsenite (AsIII) antiporter ACR3 protein is critical for As metabolism in organisms, but it is lost in flowering plants. Here, a novel ACR3 gene from As-hyperaccumulator Pteris vittata, PvACR3;1, was cloned and expressed in Saccharomyces cerevisiae (yeast), Arabidopsis thaliana (model plant), and Nicotiana tabacum (tobacco). Yeast experiments showed that PvACR3;1 functioned as an AsIII-antiporter to mediate AsIII efflux to an external medium. At 5 μM AsIII, PvACR3;1 transgenic Arabidopsis accumulated 14-29% higher As in the roots and 55-61% lower As in the shoots compared to WT control, showing lower As translocation. Besides, transgenic tobacco under 5 μM AsIII or AsV also showed similar results, indicating that expressing PvACR3;1 gene increased As retention in plant roots. Moreover, observation of PvACR3;1-green fluorescent protein fusions in transgenic Arabidopsis showed that PvACR3;1 protein localized to the vacuolar membrane, indicating that PvACR3;1 mediated AsIII sequestration into vacuoles, consistent with increased root As. In addition, soil experiments showed ∼22% lower As in the shoots of transgenic tobacco than control. Thus, our study provides a potential strategy to limit As accumulation in plant shoots, representing the first report to decrease As translocation by sequestrating AsIII into vacuoles, shedding light on engineering low-As crops to improve food safety.

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