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Abstract: Microbe–mineral interactions play an important role in affecting geochemical transformations of heavy metals in the soil environment. The formation of metal sulfide, which is mediated by sulfate-reducing bacteria (SRB) through contributing to sulfate reduction is an important pathway for heavy metal stabilization in anoxic soil. In oxic rice rhizospheres, there are abundant sulfur oxidizing bacteria (SOB) which can enhance sulfur oxidation and hence the availability of heavy metals, resulting in the uptake of such metals by the plant and a potential risk to human health. In this study, the potential existence of SRB in oxic rice rhizospheres, their contribution to sulfate reduction, and potential to reduce the availability of heavy metal was investigated. PCR-DGGE fingerprinting and real-time PCR results showed increasing numbers of SRB with Pb addition, which corresponded with increases in soil pH and reduction in Eh, suggesting the enhancement of sulfur reduction and SRB activity. Sulfur K-edge XANES, which characterized sulfur speciation in situ, revealed reduced states of sulfur. The SRB mediated the sulfate reduction and contributed to the formation of reduced sulfur which interacted with Pb, leading to the formation of stable metal sulfide and reduction of Pb availability. In return, acclimated SRB populations developed in Pb-polluted conditions. Hence stabilization of reduced sulfur by Pb enhanced the activity of SRB and sulfate reduction in rice rhizosphere. [Copyright &y& Elsevier]

Copper oxide nanoparticles (CuO NPs) are widely used as a fungicide in agriculture. The application of CuO NPs in agriculture affects the growth of rice and metal accumulation in rice. However, the mechanism of CuO NPs on arsenic (As) accumulation in rice remains unclear. In this study, a hydroponic culture was produced to investigate the mechanism of the effect of 50 and 100 mg L−1 CuO NPs on As accumulation in rice. Our results showed that CuO NPs decreased As(III/V) accumulation in the roots and shoots by adsorbing As(III/V), oxidizing of As(III) on the surface, and thickening the root cell wall. The addition of CuO NPs regulated the expression of the OsNIP1;1, OsHAC1;1, and OsHAC4 genes, which decreased As(III) transport and promoted As(V) reduction in the roots. Moreover, when CuO NPs were co-exposed to As, a negative correlation between the concentration of Cu and As in rice was also found in our study. However, CuO NPs significantly increased Cu accumulation in rice and constrained the rice growth. In conclusion, CuO NPs might be a promising way to decrease As accumulation in rice, but the negative effects such as growth inhibition should be further considered. Therefore, the application of CuO NPs in rice plants should take a more restrained approach. [ABSTRACT FROM AUTHOR]

Cd contamination in rice urgently needs to be addressed. Nano hydroxyapatite (n-HAP) is an eco-friendly material with excellent Cd fixation ability. However, due to its own high reactivity, innovative application of n-HAP in the treatment of Cd contamination in rice is needed. In this study, we proposed a new application, namely n-HAP pre-treatment, which can effectively reduce Cd accumulation in rice and alleviate Cd stress. The results showed that 80 mg/L n-HAP pre-treatment significantly reduced Cd content in rice shoot by 35.1%. Biochemical and combined transcriptomic-proteomic analysis revealed the possible molecular mechanisms by which n-HAP pre-treatment promoted rice growth and reduced Cd accumulation. (1) n-HAP pre-treatment regulated gibberellin and jasmonic acid synthesis-related pathways, increased gibberellin content and decreased jasmonic acid content in rice root, which promoted rice growth; (2) n-HAP pre-treatment up-regulated gene CATA1 expression and down-regulated gene OsGpx1 expression, which increased rice CAT activity and GSH content; (3) n-HAP pre-treatment up-regulated gene OsZIP1 expression and down-regulated gene OsNramp1 expression, which reduced Cd uptake, increased Cd efflux from rice root cells. [Display omitted] • n-HAP pre-treatment could effectively reduce Cd accumulation in rice seedlings. • n-HAP pre-treatment modulated gibberellin and jasmonic acid synthesis pathways. • n-HAP pre-treatment regulated the expression of gene CATA1 and OsGpx1. • n-HAP pre-treatment influenced Cd transport related gene OsZIP1 and OsNramp1. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) contamination in paddy soil has become a worldwide concern and severely endangered human health. Nano hydroxyapatite (n-HAP) is a practical material to manage paddy Cd pollution, but its dosage should not be excessive. Based on previous studies, we validated the effect of n-HAP pre-treatment on rice Cd uptake in pot and field experiments. The results indicated that n-HAP pre-treatment effectively restricted Cd translocation in the soil-rice system. In pot experiment, when soil n-HAP concentration was 5000 mg/kg, the Cd content in the grains of n-HAP pre-treated rice was 0.171 mg/kg, decreased by 29.3% compared with normal rice (0.242 mg/kg). In field experiment, when soil n-HAP concentration was 20,000 mg/kg, the Cd content in the grains of n-HAP pre-treated rice was 0.156 mg/kg, decreased by 35.3% compared with normal rice (0.241 mg/kg). The primary mechanism was that n-HAP pre-treatment altered the formation and composition of iron plaque and therefore enhanced the Cd binding ability of iron plaque. The available N and P content and urease activity in paddy field were increased. We further investigated the impact of n-HAP on the diversity and structure of paddy microbial communities. The Chao1 and Shannon diversity indices showed no significant difference. The relative abundance of Actinobacteria and Proteobacteria was significantly decreased by n-HAP, indicating that Cd pollution might be alleviated. Desulfobacterota , Gemmatimonadota , and Geobacteraceae were significantly enriched by n-HAP. The declining relative abundance of Basidiomycota and the increasing relative abundance of other fungal taxa also suggested that n-HAP could alleviate Cd toxicity in soil. [Display omitted] • n-HAP pre-treatment reduced Cd accumulation in rice grains effectively. • n-HAP pre-treatment restricted Cd translocation from root to stem by regulating iron plaque formation and composition. • n-HAP significantly increased available N, P content and urease activity in paddy field. • n-HAP did not significantly affect the abundance and diversity of paddy microbial communities but altered their structure. [ABSTRACT FROM AUTHOR]

Nowadays, Lead (Pb) and Cadmium (Cd) contamination in rice is an important worldwide environmental concern. Fe 3 O 4 nanoparticles (Fe 3 O 4 NPs) and Nano hydroxyapatite (n-HAP) are promising materials to manage Pb and Cd contamination. This study systematically investigated the effect of Fe 3 O 4 NPs and n-HAP on Pb and Cd stressed rice seedlings' growth, oxidative stress, Pb and Cd uptake and subcellular distribution in roots. Furthermore, we clarified the immobilization mechanism of Pb and Cd in the hydroponic system. Fe 3 O 4 NPs and n-HAP could reduce Pb and Cd uptake of rice mainly through decreasing Pb and Cd concentrations in culture solution and combining with Pb and Cd in root tissues. Pb and Cd were immobilized by Fe 3 O 4 NPs through complex sorption processes and by n-HAP through dissolution-precipitation and cation exchange, respectively. On the 7th day, 1000 mg/L Fe 3 O 4 NPs reduced the contents of Pb and Cd in shoots by 90.4% and 95.8%, in roots by 23.6% and 12.6%, 2000 mg/L n-HAP reduced the contents of Pb and Cd in shoots by 94.7% and 97.3%, in roots by 93.7% and 77.6%, respectively. Both NPs enhanced the growth of rice seedlings by alleviating oxidative stress and upregulating glutathione secretion and antioxidant enzymes activity. However, Cd uptake of rice was promoted at certain concentrations of NPs. The subcellular distribution of Pb and Cd in roots indicated that both NPs decreased the percentage of Pb and Cd in the cell wall, which was unfavorable for Pb and Cd immobilization in roots. Cautious choice was needed when using these NPs to manage rice Pb and Cd contamination. [Display omitted] • Fe 3 O 4 NPs immobilized Pb and Cd through complex sorption processes. • n-HAP immobilized Pb and Cd through dissolution-precipitation and cation exchange. • Cd accumulation in rice roots could increase due to using Fe 3 O 4 NPs and n-HAP. • Fe 3 O 4 NPs and n-HAP decreased the percentage of Pb and Cd in the cell wall. [ABSTRACT FROM AUTHOR]

The toxic chemical element cadmium (Cd) in paddy fields triggered increasing problems of growth inhibition and food security in rice consistently. In this study, we found Metarhizium robertsii , which is widely used as a bioinsecticide and biofertilizer in agriculture and recently found to be resistant to Cd, developed intraradical and extraradical symbiotic hyphae in rice seedlings, and successfully colonized in the rice rhizosphere soil to more than 103 CFUs g−1 soil at harvesting. M. robertsii colonization significantly reduced Cd accumulations in both hydroponically cultured seedlings and the matured rice cultured in Cd contaminated potting soil (2 ppm). Notably, Cd accumulation reduction of the roots, stems, leaves, husks and grains of the matured rice induced by the fungus were 44.3%, 32.1%, 35.3%, 31.9% and 24.7%, respectively. It was caused by the M. robertsii -induced suppression of Cd intake transporter gene osNramp5 in the rice roots, and the chemical stabilizing of Cd to the residual fraction in the rhizosphere soil. In addition, the colonization of M. robertsii significantly promoted the growth characters and the photosynthesis of the rice plants. This is achieved by the increase of endogenous hormone levels of indole-3-acetic, gibberellin A 3 and brassinolide induced by M. robertsii. Furthermore, the fungus enhanced the antioxidative capacities via increasing enzyme activities of catalase, peroxidase and the production of glutathione, ascorbic acid, proline in the rice plants. Our work provides theoretical basis for expanding the use of M. robertsii as in situ Cd accumulation reduction and detoxification agents for rice in contaminated paddy fields. [Display omitted] • M. robertsii colonized well in the rice roots and the rhizosphere soil. • M. robertsii reduced Cd accumulation and promoted plant growth of rice. • Rice osNramp5 was suppressed and soil Cd ions were stabilized by the fungus. • Endogenous phytohormones IAA, GA 3 and BL were elevated by the fungus. • M. robertsii stimulated antioxidative capacities of rice. [ABSTRACT FROM AUTHOR]

Due to the high migration capacity in agricultural soil-crop systems, cadmium (Cd) is accumulated in various crops and severely inhibits plant growth. In this study, we showed that, under Cd stress, the plant-symbiotic fungus Metarhizium robertsii reduced Cd accumulation in Arabidopsis thaliana shoots and roots by 21.8 % and 23.8 %, respectively. This is achieved by M. robertsii colonization-induced elevation of Cd efflux capacity via upregulation of three PCR genes, which is confirmed by the fact that the extent to which M. robertsii reduced Cd accumulation in the WT plants was greater than the inactivating mutants of the PCR genes. M. robertsii also alleviated Cd-induced leaf etiolation in A. thaliana by increasing the chlorophyll amount and modified plant physiological status to increase Cd stress tolerance via increasing production of catalase, peroxidase and glutathione and upregulating multiple HIPP proteins involved in sequestration of Cd. Notably, consistent with that in A. thaliana , the colonization of M. robertsii also reduced the Cd accumulation in Oryza sativa seedlings by upregulating the PCR gene OsPCR1 , and increased chlorophyll amount and alleviated oxidative stress. Therefore, M. robertsii colonization reduced Cd accumulation in plants, and promoted plant growth and health by elevating Cd efflux capacity and modifying physiological status. [Display omitted] • M. robertsii reduces Cd content in A. thaliana and O. sativa by increasing the PCR genes to elevate the Cd efflux capacity. • Cd-induced leaf etiolation was alleviated and more chlorophyll was produced in plants colonized with M. robertsii. • M. robertsii decreased the oxidation level and increased the total antioxidant capacity in plants. [ABSTRACT FROM AUTHOR]

Natural organic matter (NOM) can interact with engineered nanoparticles (NPs) in the environment and modify their behavior and toxicity to organisms. In the present study, the phytotoxicity of copper oxide (CuO) NPs to rice seedlings in the presence of humic acid as a model NOM was investigated. The results showed that CuO NPs induced the inhibition of root elongation, aberrations in root morphology and ultrastructure, and losses of cell viability and membrane integrity. The adverse effects partly resulted from the generation of reactive oxygen species caused by CuO NPs, which led to lipid peroxidation, mitochondrial dysfunction, and programmed cell death in rice seedlings. However, all the phytotoxicity was alleviated with the addition of humic acid because humic acid coatings on nanoparticle surfaces enhanced electrostatic and steric repulsion between the CuO NPs and the plant cell wall/membrane, reducing contact between NPs and plant and CuO NP-induced oxidative damage to plant cells. The present study's results shed light on the mechanism underlying NP phytotoxicity and highlight the influence of NOM on the bioavailability and toxicity of NPs. Environ Toxicol Chem 2015;34:1996-2003. © 2015 SETAC [ABSTRACT FROM AUTHOR]

Lead (Pb) and arsenic (As) exist in soil with different ionic forms, and it is difficult to immobilize simultaneously Pb and As in soil. The objective of this study is to determine the effects of water management including flooding (FL), alternate wetting and drying (AWD) and dry farming (DF) combined with addition of phosphate (P) on the accumulation of Pb and As in rice. Our results showed that Pb accumulated in root during vegetative stage, and most of As in root was transported to the above ground parts during the reproductive stage. Pb was evenly distributed in grains, and As was mostly accumulated in bran and aleurone layer. Water management had a reverse effect on the accumulation of Pb and As in rice. However, the effects of P on arid soil environment and Pb, As accumulation in rice were stronger than that in flooded soil. Application of P under AWD treatment could maintain a similar quantity of Fe plaque with flooding, decrease the availability of Pb in rhizosphere soil, reduce Pb and As accumulation in root, and result in the reduction of Pb and As accumulation in grains by 86% and 66% respectively. Besides, our study also found that flooding or AWD during vegetative stage facilitated the formation of iron plaque. In conclusion, AWD combined with P application could maintain a relatively lower concentrations of Pb and As in grains. [Display omitted] • Lead accumulated in root primarily during the vegetative stage. • Arsenic in root was transported to aboveground parts during the reproductive stage. • Flooding or AWD during the vegetative stage in soil would help to form iron plaque. • AWD combined with application of P could decrease simultaneously lead and arsenic in grains. • Lead was distributed evenly in grains, and arsenic was mostly accumulated in bran and aleurone layer. [ABSTRACT FROM AUTHOR]

Abstract: A pot experiment was carried out to study the sulfur (S) and lead (Pb) interaction and its impact on soil microbial community composition in rice rhizosphere soil under flooded conditions. Paddy soil was treated with a Pb gradient with and without thiosulfate addition and then planted with rice. The increasing addition of Pb resulted in plant yield reduction and high, phytotoxic concentrations of Pb in roots with relatively low concentration of Pb in shoots. Under the impact of thiosulfate, Pb uptake in plants and NH4OAc extractable Pb did not increase dramatically. PCR-DGGE experiment suggested that S action led to new bands. Specific clones (T3 and T6) found in S addition soils had high similarity to Thiobacillus, which indicated relatively high rates of potential S oxidation. S addition did not affect the availability Pb and the composition of soil microbial community. S addition is not a suitable amendatory tool of phytoremediation for Pb polluted soil. [Copyright &y& Elsevier]

To determine the bioavailability and translocation of metal oxide nanoparticles (MONPs) in the soil-rice plant system, we examined the accumulation and micro-distribution of ZnO nanoparticles (NPs), CuO NPs and CeO 2 NPs (50, 100 and 500 mg/kg) in the paddy soil and rice plants under flooded condition for 30 days using single-step chemical extraction and diffusive gradients in thin films (DGT) technique combined with micro X-ray fluorescence spectroscopy (μ-XRF). The results show that various MONPs changed the soil properties, especially the redox potential was enhanced to −165.33 to −75.33 mV compared to the control. The extraction efficiency of Zn, Cu and Ce in the paddy soil from high to low was EDTA, DTPA, CaCl 2 and DGT. Moreover, exposure to 500 mg/kg CuO NPs and CeO 2 NPs induced the primary accumulation of Cu and Ce elements in rice roots as high as 235.48 mg Cu/kg and 164.84 mg Ce/kg, respectively, while the Zn concentration in shoots was up to 313.18 mg/kg under highest ZnO NPs with a 1.5 of translocation factor. The effect of MONPs on the plant growth was mainly related to the chemical species and solubility of MONPs. Micro-XRF analysis shows that Zn was mostly located in the root cortex while Cu was primarily accumulated in the root exodermis and few Ce distributed in the root. Pearson correlation coefficients indicate that only DTPA-extracted metals in soil were significantly and well correlated to the Zn, Cu and Ce accumulation in rice seedlings exposed to MONPs. This work is of great significance for evaluating the environmental risks of MONPs in soil and ensuring the safety of agricultural products. Unlabelled Image • Various MONPs altered the soil properties, especially the redox potential. • DTPA was more suitable for evaluating the bioavailability of MONPs. • DGT could hardly extract heavy metals from the MONP-amended soil. • ZnO NPs caused much higher accumulation and translocation of Zn in the rice plants. [ABSTRACT FROM AUTHOR]