Arsenic (As) and cadmium (Cd) are two toxic elements that have a relatively high risk of transfer from paddy soil to rice grain. Rice is a major dietary source of these two elements for populations consuming rice as a staple food. Reducing their accumulation in rice grain is important for food safety and human health. We review recent progress in understanding the biogeochemical processes controlling As and Cd bioavailability in paddy soil, the mechanisms of their uptake, translocation and detoxification in rice plants, and strategies to reduce their accumulation in rice grain. Similarities and differences between the two elements are emphasized. Some knowledge gaps are also identified. The concentrations of As and Cd in rice grain vary by three orders of magnitude, depending on the bioavailability of the two elements in soil, rice genotype and growing conditions. The redox potential in paddy soil has a profound but opposite effect on As and Cd bioavailability, whereas soil pH affects Cd bioavailability more than As bioavailability. A number of key genes involved in As and Cd uptake, translocation, sequestration, and detoxification in rice have been characterized. Allelic variations of several genes underlying the variations in Cd accumulation have been identified, but more remains to be elucidated, especially for As. Two types of strategies can be used to reduce As and Cd accumulation, reducing their bioavailability in soil or their uptake and translocation in rice. Reducing the accumulation of both As and Cd in rice simultaneously remains a great challenge.

/pdf/arsenic-and-cadmium-accumulation-in-rice-and-mitigation-9hejn47t27.pdf

Arsenic and cadmium accumulation in rice and mitigation strategies

This paper is the first multi-country investigation of comprehensive corporate risk disclosure. Based on a detailed content analysis of 160 annual reports, we analyze the attributes and the quantity of risk disclosure and its association with the level of firm risk in the U.S., Canadian, U.K., and German settings. We find a consistent pattern where risk disclosure is most prevalent in management reports, concentrates on financial risk categories, and comprises little quantitative and forward-looking disclosure across sample countries. In terms of risk disclosure quantity, U.S. firms generally dominate, followed by German firms. Cross-country variation in risk disclosure attributes can only partly be linked to domestic disclosure regulation, suggesting that risk disclosure incentives play an important role. While risk disclosure quantity appears to be positively associated with proxies of firm risk in the North American settings, we find a negative association with leverage for Germany. This coin...

Attributes of Corporate Risk Disclosure: An International Investigation in the Manufacturing Sector

Purpose – This study aims to measure the extent of mandatory and voluntary risk reporting and investigate the impact of competition, corporate governance and ownership structure on risk reporting practices in annual reports of Egyptian companies. Design/methodology/approach – A number of theoretical perspectives including proprietary cost, agency theory, stakeholder theory, political cost, signalling theory and legitimacy theory are used to derive research hypotheses and identify the potential determinants of risk reporting practices in the annual reports of Egyptian companies. The annual reports of 105 listed companies for 2007 were examined to measure the extent of risk reporting and examine potential determinants of risk reporting. An unweighted disclosure index, based on Egyptian Accounting Standards (EAS) 25, has been used to measure the level of mandatory risk reporting while content analysis – sentence approach – is used in coding voluntary risk reporting. Multiple regression analysis is used in ev...

Competition, corporate governance, ownership structure and risk reporting

Rice is a major dietary source of the toxic metal, cadmium (Cd). Previous studies reported that the rice transporter, OsNRAMP1, (Natural resistance-associated macrophage protein 1) could transport iron (Fe), Cd and arsenic (As) in heterologous yeast assays. However, the in planta function of OsNRAMP1 remains unknown. Here, we showed that OsNRAMP1 was able to transport Cd and manganese (Mn) when expressed in yeast, but did not transport Fe or As. OsNRAMP1 was mainly expressed in roots and leaves and encoded a plasma membrane-localized protein. OsNRAMP1 expression was induced by Cd treatment and Fe deficiency. Immunostaining showed that OsNRAMP1 was localized in all root cells, except the central vasculature, and in leaf mesophyll cells. The knockout of OsNRAMP1 resulted in significant decreases in root uptake of Cd and Mn and their accumulation in rice shoots and grains, and increased sensitivity to Mn deficiency. The knockout of OsNRAMP1 had smaller effects on Cd and Mn uptake than knockout of OsNRAMP5, while knockout of both genes resulted in large decreases in the uptake of the two metals. Taken together, OsNRAMP1 contributes significantly to the uptake of Mn and Cd in rice, and the functions of OsNRAMP1 and OsNRAMP5 are similar but not redundant.

OsNRAMP1 transporter contributes to cadmium and manganese uptake in rice

Plant Nutrition for Human Nutrition: Hints from Rice Research and Future Perspectives

Rice is a major dietary source of the toxic metalloid arsenic. Reducing arsenic accumulation in rice grain is important for food safety. We generated transgenic rice overexpressing two aquaporin genes, OsNIP1;1 and OsNIP3;3, under the control of a maize ubiquitin promoter or the rice OsLsi1 promoter, and tested the effect on arsenite uptake and translocation. OsNIP1;1 and OsNIP3;3 were highly permeable to arsenite in Xenopus oocyte assays. Both transporters were localized at the plasma membrane. Knockout of either gene had little effect on arsenite uptake or translocation. Overexpression of OsNIP1;1 or OsNIP3;3 in rice did not affect arsenite uptake but decreased root-to-shoot translocation of arsenite and shoot arsenic concentration markedly. The overexpressed OsNIP1;1 and OsNIP3;3 proteins were localized in all root cells without polarity. Expression of OsNIP1;1 driven by the OsLsi1 promoter produced similar effects. When grown in two arsenic-contaminated paddy soils, overexpressing lines contained significantly lower arsenic concentration in rice grain than the wild-type without compromising plant growth or the accumulation of essential nutrients. Overexpression of OsNIP1;1 or OsNIP3;3 provides a route for arsenite to leak out of the stele, thus restricting arsenite loading into the xylem. This strategy is effective in reducing arsenic accumulation in rice grain.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/nph.15190

Decreasing arsenic accumulation in rice by overexpressing OsNIP1;1 and OsNIP3;3 through disrupting arsenite radial transport in roots

This study aims to examine the relationship between corporate characteristics and level of risk reporting and to reveal the impact of issuing regulatory guidelines on risk reporting in annual reports. One hundred non-financial companies were randomly selected from the first section of the Tokyo Stock Exchange. Firstly, we find that, consistent with prior research, the size of the company and the number of risk disclosures are positively correlated. On the other hand, no significant relationship exists between the number of risk disclosures and other corporate characteristics. Secondly, the findings show that most of the companies disclose descriptive risk information but are reluctant to quantify risk. It also shows that the level of risk reporting has increased, at least in quantity, in annual reports after the issuance of regulatory guidelines on risk reporting by the Financial Service Agency.

Risk reporting of Japanese companies and its association with corporate characteristics

Rice is a major dietary source of the toxic metal cadmium (Cd), and reducing its accumulation in the grain is therefore important for food safety. We selected two cultivars with contrasting Cd accumulation and generated transgenic lines overexpressing OsNRAMP5, which encodes a major influx transporter for manganese (Mn) and Cd. We used two different promoters to control the expression, namely OsActin1 and maize Ubiquitin. Overexpression of OsNRAMP5 increased Cd and Mn uptake into the roots, but markedly decreased Cd accumulation in the shoots, whilst having a relatively small effect on Mn accumulation in the shoots. The overexpressed OsNRAMP5 protein was localized to the plasma membrane of all cell types in the root tips and lateral root primordia without polarity. Synchrotron X-ray fluorescence mapping showed that the overexpression lines accumulated more Cd in the root tips and lateral root primordia compared with the wild-type. When grown in three Cd-contaminated paddy soils, overexpression of OsNRAMP5 decreased concentration of Cd in the grain by 49-94% compared with the wild type. OsNRAMP5-overexpression plants had decreased Cd translocation from roots to shoots as a result of disruption of its radial transport into the stele for xylem loading, demonstrating the effect of transporter localization and polarity on ion homeostasis.

/pdf/overexpression-of-the-manganese-cadmium-transporter-osnramp5-3yutf6qk0i.pdf

Overexpression of the manganese/cadmium transporter OsNRAMP5 reduces cadmium accumulation in rice grain.

Ammonium is a preferential nitrogen form for rice (Oryza sativa) grown in paddy field, but the molecular mechanisms for ammonium uptake have not been well understood. We functionally characterized three members belonging to ammonium transporter 1 (AMT1) and investigated their contributions to ammonium uptake. Spatial expression analysis showed that the upregulated expression of OsAMT1;1 and OsAMT1;2 and downregulated expression of OsAMT1;3 by ammonium were higher in the root mature region than in the root tips. All OsAMT1 members were polarly localized at the distal side of exodermis in the mature region of crown roots and lateral roots. Upon exposure to ammonium, localization of OsAMT1;1 and OsAMT1;2 was also observed in the endoplasmic reticulum, but their abundance in the plasma membrane was not changed. Single knockout of either gene did not affect ammonium uptake, but knockout of all three genes resulted in 95% reduction of ammonium uptake. However, the nitrogen uptake did not differ between the wild-type rice and triple mutants at high ammonium and nitrate supply. Our results indicate that three OsAMT1 members are cooperatively required for uptake of low ammonium in rice roots and that they undergo a distinct regulatory mechanism in response to ammonium.

Three polarly localized ammonium transporter 1 members are cooperatively responsible for ammonium uptake in rice under low ammonium condition.

The study attempts to analyze the ins and outs of the risk reporting guidelines in UK. The guidelines advocate for the voluntary adoption of risk reporting through annual reports of the company. This voluntary reporting of risk will ensure the transparency and efficiency of the company management that eventually help the company to obtain funds from the capital market with the possible lowest cost. They also advise to disclose material / relevant risk information in a proper way so that the users can take their economic decision based on those disclosed information. On the other hand, company need not to disclose the commercially sensitive risk information, as it can give advantage to the rival companies. This risk reporting guidelines are also having some weaknesses. Such as, they mention about inverse relationship between level of disclosed risk information and cost of capital without any empirical evidence. Guidelines give a vague direction about the commercial sensitive risk information because companies can hide some important risk information on the ground of commercial sensitivity if needed. Other lacking include unavailability of suitable / reliable risk identification and measurement tools, expectation about common knowledge and so on.

Noriyuki Konishi

Papers

Decreasing arsenic accumulation in rice by overexpressing OsNIP1;1 and OsNIP3;3 through disrupting arsenite radial transport in roots

Risk reporting of Japanese companies and its association with corporate characteristics

Overexpression of the manganese/cadmium transporter OsNRAMP5 reduces cadmium accumulation in rice grain.

Three polarly localized ammonium transporter 1 members are cooperatively responsible for ammonium uptake in rice under low ammonium condition.

The UK Guidelines for Company Risk Reporting−An Evaluation