Contamination of cadmium (Cd) in paddy soil is a serious environmental problem threatening food safety in some parts of southern China, where rice grain Cd concentration often exceeds the Chinese ...limit (0.2 mg kg−1). We tested the effect of CaCO3 liming combined with growing low Cd cultivars on Cd accumulation in rice grain in 2-year field trials. A liming model was used to predict the doses of lime required. Lime (2.25–7.5 t ha−1) was applied in 2016 only and the effect monitored in both 2016 and 2017. Soil pH was increased from the initial 5.5 to the target value 6.5 by 7.5 t ha−1 CaCO3. Liming greatly reduced CaCl2-extractable Cd in the rhizospheric soil. Grain Cd concentration in the control exceeded the limit by 2–5 times. Liming at 7.5 t ha−1 decreased grain Cd concentration by 70–80% in both seasons without affecting grain yield. Grain Cd concentration was below the limit in the 7.5 t ha−1 liming treatment in both seasons. Grain Cd concentration correlated closely with CaCl2-extractable Cd in rhizospheric soil at the grain maturing stage. Seasonal difference in grain Cd concentration was attributed to the soil water status at the grain maturing stage. Liming had no significant effect on grain arsenic concentration or speciation. A single application of CaCO3 to raise soil pH to 6.5, combined with low Cd cultivars and delayed drainage of paddy water during late grain filling stage, was highly effective at reducing Cd accumulation in rice grain.
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•High phytoavailability of Cd in a moderately contaminated paddy soil.•Rice Cd concentration in the control exceeded the Chinese limit by 2–5 times.•Liming with 7.5 t ha−1 CaCO3 decreased grain Cd concentration by 70–80%.•Liming combined low Cd cultivars and delayed drainage was highly effective.
Background and aims Cereals are the main dietary source of cadmium (Cd). Rice grains often contain higher levels of Cd than other cereals, but the reasons are unknown. The aims of this study were to ...compare Cd uptake, translocation and influx kinetics between rice, wheat and maize and to investigate whether the expression and functionality of Nramp5 genes differ between the three crop species. Methods Two cultivars each of rice, wheat and maize were grown hydroponically and exposed to a range of Cd concentrations. Nramp5 genes were cloned from the three plants and their expression levels determined. The Cd transport activities of Nramp5 proteins were tested in yeast. Results Under hydroponic conditions, Cd uptake in rice was 2.5–8.1 and 1.1–3.6 times that of wheat and maize, respectively. The maximum Cd influx velocity of rice was 6.5 and 2.2 times that in wheat and maize, respectively. Wheat showed the lowest Cd uptake but the highest Cd root-to-shoot translocation. The absolute expression level of OsNramp5 in rice roots was 4–5 times that of TaNramp5A and TaNramp5D in wheat or ZmNramp5 in maize. All Nramp5 proteins were localized to the plasma membrane. When expressed in yeast, OsNramp5 showed a greater Cd transport activity than wheat or maize Nramp5. Conclusions Rice has a greater Cd uptake ability than wheat or maize, likely because OsNramp5 is more highly expressed and the protein has a higher Cd transport activity than wheat or maize Nramp5.
Cadmium (Cd) is phytotoxic and detoxified primarily via phytochelatin (PC) complexation in Arabidopsis. Here, we explore Cd toxicity responses and defence mechanisms beyond the PC pathway using ...forward genetics approach. We isolated an Arabidopsis thaliana Cd‐hypersensitive mutant, Cd‐induced short root 1 (cdsr1) in the PC synthase mutant (cad1‐3) background. Using genomic resequencing and complementation, we identified PP2A‐4C as the causal gene for the mutant phenotype, which encodes a catalytic subunit of protein phosphatase 2A (PP2A). Root and shoot growth of cdsr1 cad1‐3 and cdsr1 were more sensitive to Cd than their respective wild‐type cad1‐3 and Col‐0. A mutant of the PP2A scaffolding subunit 1A was also more sensitive to Cd. PP2A‐4C was localized in the cytoplasm and nucleus and PP2A‐4C expression was downregulated by Cd in cad1‐3. PP2A enzyme activity was decreased in cdsr1 and cdsr1 cad1‐3 under Cd stress. The expression of 1‐aminocyclopropane‐1‐carboxylic acid synthase genes ACS2 and ACS6 was upregulated by Cd more in cad1‐3 and cdsr1 cad1‐3 than in Col‐0 and the double mutant had a higher ACS activity. cdsr1 cad1‐3 and cdsr1 overproduced ethylene under Cd stress. The results suggest that PP2A containing 1A and 4C subunits alleviates Cd‐induced growth inhibition by modulating ethylene production.
We used a forward genetics approach to isolate and characterize an Arabidopsis Cd‐sensitive mutant, Cd‐induced short root 1 (cdsr1), which has a point mutation in the protein phosphatase 2A (PP2A) subunit 4C. The mutant overproduced ethylene in response to Cd. PP2A alleviates Cd‐induced growth inhibition by modulating ethylene production, likely through dephosphorylation of 1‐aminocyclopropane‐1‐carboxylic acid synthases. Our study sheds light on the regulation of ethylene production in response to Cd stress.
Arsenic (As) is an important environmental and food-chain toxin. We investigated the key components controlling As accumulation and tolerance in Arabidopsis thaliana.
We tested the effects of ...different combinations of gene knockout, including arsenate reductase (HAC1), γ-glutamyl-cysteine synthetase (γ-ECS), phytochelatin synthase (PCS1) and phosphate effluxer (PHO1), and the heterologous expression of the As-hyperaccumulator Pteris vittata arsenite efflux (PvACR3), on As tolerance, accumulation, translocation and speciation in A. thaliana.
Heterologous expression of PvACR3 markedly increased As tolerance and root-to-shoot As translocation in A. thaliana, with PvACR3 being localized to the plasma membrane. Combining PvACR3 expression with HAC1 mutation led to As hyperaccumulation in the shoots, whereas combining HAC1 and PHO1 mutation decreased As accumulation. Mutants of γ-ECS and PCS1 were hypersensitive to As and had higher root-to-shoot As translocation. Combining γ-ECS or PCS1 with HAC1 mutation did not alter As tolerance or accumulation beyond the levels observed in the single mutants.
PvACR3 and HAC1 have large effects on root-to-shoot As translocation. Arsenic hyperaccumulation can be engineered in A. thaliana by knocking out the HAC1 gene and expressing PvACR3. PvACR3 and HAC1 also affect As tolerance, but not to the extent of γ-ECS and PCS1.
China faces great challenges in protecting its soil from contamination caused by rapid industrialization and urbanization over the last three decades. Recent nationwide surveys show that 16% of the ...soil samples, 19% for the agricultural soils, are contaminated based on China’s soil environmental quality limits, mainly with heavy metals and metalloids. Comparisons with other regions of the world show that the current status of soil contamination, based on the total contaminant concentrations, is not worse in China. However, the concentrations of some heavy metals in Chinese soils appear to be increasing at much greater rates. Exceedance of the contaminant limits in food crops is widespread in some areas, especially southern China, due to elevated inputs of contaminants, acidic nature of the soil and crop species or cultivars prone to heavy metal accumulation. Minimizing the transfer of contaminants from soil to the food chain is a top priority. A number of options are proposed, including identification of the sources of contaminants to agricultural systems, minimization of contaminant inputs, reduction of heavy metal phytoavailability in soil with liming or other immobilizing materials, selection and breeding of low accumulating crop cultivars, adoption of appropriate water and fertilizer management, bioremediation, and change of land use to grow nonfood crops. Implementation of these strategies requires not only technological advances, but also social-economic evaluation and effective enforcement of environmental protection law.
Summary Background Screening for human papillomavirus (HPV) infection is more effective in reducing the incidence of cervical cancer than screening using Pap smears. Moreover, HPV testing can be done ...on a vaginal sample self-taken by a woman, which offers an opportunity to improve screening coverage. However, the clinical accuracy of HPV testing on self-samples is not well-known. We assessed whether HPV testing on self-collected samples is equivalent to HPV testing on samples collected by clinicians. Methods We identified relevant studies through a search of PubMed, Embase, and CENTRAL. Studies were eligible for inclusion if they fulfilled all of the following selection criteria: a cervical cell sample was self-collected by a woman followed by a sample taken by a clinician; a high-risk HPV test was done on the self-sample (index test) and HPV-testing or cytological interpretation was done on the specimen collected by the clinician (comparator tests); and the presence or absence of cervical intraepithelial neoplasia grade 2 (CIN2) or worse was verified by colposcopy and biopsy in all enrolled women or in women with one or more positive tests. The absolute accuracy for finding CIN2 or worse, or CIN grade 3 (CIN3) or worse of the index and comparator tests as well as the relative accuracy of the index versus the comparator tests were pooled using bivariate normal models and random effect models. Findings We included data from 36 studies, which altogether enrolled 154 556 women. The absolute accuracy varied by clinical setting. In the context of screening, HPV testing on self-samples detected, on average, 76% (95% CI 69–82) of CIN2 or worse and 84% (72–92) of CIN3 or worse. The pooled absolute specificity to exclude CIN2 or worse was 86% (83–89) and 87% (84–90) to exclude CIN3 or worse. The variation of the relative accuracy of HPV testing on self-samples compared with tests on clinician-taken samples was low across settings, enabling pooling of the relative accuracy over all studies. The pooled sensitivity of HPV testing on self-samples was lower than HPV testing on a clinician-taken sample (ratio 0·88 95% CI 0·85–0·91 for CIN2 or worse and 0·89 0·83–0·96 for CIN3 or worse). Also specificity was lower in self-samples versus clinician-taken samples (ratio 0·96 0·95–0·97 for CIN2 or worse and 0·96 0·93–0·99 for CIN3 or worse). HPV testing with signal-based assays on self-samples was less sensitive and specific than testing on clinician-based samples. By contrast, some PCR-based HPV tests generally showed similar sensitivity on both self-samples and clinician-based samples. Interpretation In screening programmes using signal-based assays, sampling by a clinician should be recommended. However, HPV testing on a self-sample can be suggested as an additional strategy to reach women not participating in the regular screening programme. Some PCR-based HPV tests could be considered for routine screening after careful piloting assessing feasibility, logistics, population compliance, and costs. Funding The 7th Framework Programme of the European Commission, the Belgian Foundation against Cancer, the International Agency for Research on Cancer, and the German Guideline Program in Oncology.
Reductive mobilization of arsenic (As) in paddy soils under flooded conditions is an important reason for the relatively high accumulation of As in rice, posing a risk to food safety and human ...health. The extent of As mobilization varies widely among paddy soils, but the reasons are not well understood. In this study, we investigated As mobilization in six As-contaminated paddy soils (total As ranging from 73 to 122 mg kg−1) in flooded incubation and pot experiments. Arsenic speciation in the solution and solid phases were determined. The magnitude of As mobilization into the porewater varied by > 100 times among the six soils. Porewater As concentration correlated closely with the concentration of oxalate-extractable As, suggesting that As associated with amorphous iron (oxyhydr)oxides represents the potentially mobilizable pool of As under flooded conditions. Soil containing a high level of manganese oxides showed the lowest As mobilization, likely because Mn oxides retard As mobilization by slowing down the drop of redox potential upon soil flooding and maintaining a higher arsenate to arsenite ratio in the solid and solution phases. Additions of a synthetic Mn oxide (hausmannite) to two paddy soils increased arsenite oxidation, decreased As mobilization into the porewater and decreased As concentrations in rice grain and straw. Consistent with previous studies using simplified model systems or pure mineral phases, the present study shows that Mn oxides and amorphous Fe (oxyhydr)oxides are important factors controlling reductive As mobilization in As-contaminated paddy soils. In addition, this study also suggests a potential mitigation strategy using exogenous Mn oxides to decrease As uptake by rice in paddy soils containing low levels of indigenous Mn oxides, although further work is needed to verify its efficacy and possible secondary effects under field conditions.
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•Reductive arsenic mobilization differed by > 100 times among six paddy soils with similar total As.•Oxalate-extractable As was a good indicator of potentially mobilizable As.•Indigenous soil Mn oxide content influenced As speciation and mobilization in paddy soil.•Addition of synthetic Mn oxide decreased reductive As mobilization and As uptake by rice.
Arsenic mobilization in flooded paddy soils correlates with oxalate-extractable As and is also affected by manganese oxides.
Although urine‐based human papillomavirus (HPV) detection is promising in cervical cancer screening, it has not yet been well‐developed. Women aged 30–65 were invited to participate in the current ...study to provide one urine and two paired vaginal samples. Urine was detected by polymerase chain reaction (PCR)‐based HPV test (urine‐based HPV test). Two vaginal samples were tested by careHPV and GenPlex® HPV genotyping assay, respectively. Women with vaginal HPV positive were called back for colposcopy and biopsied if clinically indicated. The consistency was 79.0% (κ = 0.563) and 80.5% (κ = 0.605) between the urine‐based HPV test, careHPV test, and GenPlex® HPV genotyping assay. Against CIN2 detection, the careHPV test showed 77.4% sensitivity, and 71.0% specificity, while the GenPlex® HPV genotyping assay had a sensitivity of 100% and a specificity of 58.7%. For urine‐based HPV test, the corresponding rates were 96.8% and 58.7%. Moreover, no significant differences were observed between the urine‐based HPV test and careHPV test (p = 0.3395) and GenPlex® HPV genotyping assay (p = 0.338). The newly developed urine‐based HPV test demonstrated acceptable consistency and comparable clinical performance with referenced HPV tests for vaginal samples. Therefore, urine‐based HPV detection could be a useful alternative for women with difficulties to access cervical cancer screening.
Arsenic (As) is an environmental and food chain contaminant. Excessive accumulation of As, particularly inorganic arsenic (As(i)), in rice (Oryza sativa) poses a potential health risk to populations ...with high rice consumption. Rice is efficient at As accumulation owing to flooded paddy cultivation that leads to arsenite mobilization, and the inadvertent yet efficient uptake of arsenite through the silicon transport pathway. Iron, phosphorus, sulfur, and silicon interact strongly with As during its route from soil to plants. Plants take up arsenate through the phosphate transporters, and arsenite and undissociated methylated As species through the nodulin 26-like intrinsic (NIP) aquaporin channels. Arsenate is readily reduced to arsenite in planta, which is detoxified by complexation with thiol-rich peptides such as phytochelatins and/or vacuolar sequestration. A range of mitigation methods, from agronomic measures and plant breeding to genetic modification, may be employed to reduce As uptake by food crops.
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