Plant science: the key to preventing slow cadmium poisoning
TL;DR: Recent studies on rice (Oryza sativa) and Cd-hyperaccumulating plants that have led to important insights into the processes controlling the passage of Cd from the soil to edible plant organs are reviewed.
About: This article is published in Trends in Plant Science.The article was published on 2013-02-01. It has received 775 citations till now.
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TL;DR: Proteins mediating the uptake of arsenic and cadmium have been identified, and the speciation and biotransformations of arsenic are now understood, and factors controlling the efficiency of root-to-shoot translocation and the partitioning of toxic elements through the rice node have also been identified.
Abstract: Arsenic, cadmium, lead, and mercury are toxic elements that are almost ubiquitously present at low levels in the environment because of anthropogenic influences. Dietary intake of plant-derived food represents a major fraction of potentially health-threatening human exposure, especially to arsenic and cadmium. In the interest of better food safety, it is important to reduce toxic element accumulation in crops. A molecular understanding of the pathways responsible for this accumulation can enable the development of crop varieties with strongly reduced concentrations of toxic elements in their edible parts. Such understanding is rapidly progressing for arsenic and cadmium but is in its infancy for lead and mercury. Basic discoveries have been made in Arabidopsis, rice, and other models, and most advances in crops have been made in rice. Proteins mediating the uptake of arsenic and cadmium have been identified, and the speciation and biotransformations of arsenic are now understood. Factors controlling the efficiency of root-to-shoot translocation and the partitioning of toxic elements through the rice node have also been identified.
745 citations
Cites background from "Plant science: the key to preventin..."
...Nonoccupational Cd exposure of the (nonsmoking) general population is >90% attributable to the ingestion of cereals, vegetables, and other plant-derived food (21, 29)....
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...5 μg per kilogram of body weight (29), a level that is near the average intake around the world (21)....
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TL;DR: Recent work on the genetic and molecular mechanisms of plant abiotic stress and nutrient limitation sensing and signaling is summarized and new directions for future studies are discussed.
Abstract: Abiotic stresses and soil nutrient limitations are major environmental conditions that reduce plant growth, productivity and quality. Plants have evolved mechanisms to perceive these environmental challenges, transmit the stress signals within cells as well as between cells and tissues, and make appropriate adjustments in their growth and development in order to survive and reproduce. In recent years, significant progress has been made on many fronts of the stress signaling research, particularly in understanding the downstream signaling events that culminate at the activation of stress- and nutrient limitation-responsive genes, cellular ion homeostasis, and growth adjustment. However, the revelation of the early events of stress signaling, particularly the identification of primary stress sensors, still lags behind. In this review, we summarize recent work on the genetic and molecular mechanisms of plant abiotic stress and nutrient limitation sensing and signaling and discuss new directions for future studies.
535 citations
Cites background from "Plant science: the key to preventin..."
...through transporter proteins evolved for the uptake of essential elements with similar chemical properties to Cd, such as Fe, Zn and Mn (Clemens et al., 2013)....
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...The uptake of Cd by plant roots is generally through transporter proteins evolved for the uptake of essential elements with similar chemical properties to Cd, such as Fe, Zn and Mn (Clemens et al., 2013)....
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TL;DR: This review provides a comprehensive account of the relative impact of the THMs As, Cd, Cr(VI), Hg, and Pb on the authors' total environment.
Abstract: Certain five heavy metals viz. arsenic (As), cadmium (Cd), chromium (Cr)(VI), mercury (Hg), and lead (Pb) are non-threshold toxins and can exert toxic effects at very low concentrations. These heavy metals are known as most problematic heavy metals and as toxic heavy metals (THMs). Several industrial activities and some natural processes are responsible for their high contamination in the environment. In recent years, high concentrations of heavy metals in different natural systems including atmosphere, pedosphere, hydrosphere, and biosphere have become a global issue. These THMs have severe deteriorating effects on various microorganisms, plants, and animals. Human exposure to the THMs may evoke serious health injuries and impairments in the body, and even certain extremities can cause death. In all these perspectives, this review provides a comprehensive account of the relative impact of the THMs As, Cd, Cr(VI), Hg, and Pb on our total environment.
527 citations
TL;DR: To eliminate the long-term risk of Cd entering the food chain, soils contaminated by Cd should be cleaned up when cost-effective remediation measures are available.
491 citations
Cites background from "Plant science: the key to preventin..."
...Identification of the major transporter genes and understanding on their roles in Cd accumulation in rice provide avenues for effective reduction of Cd content in rice grains (Clemens et al., 2013)....
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...In fact, plant breeding exploiting the genetic variability has been investigated as a means of reducing the accumulation of Cd in a variety of crop species (Clemens et al., 2013; Grant et al., 2008)....
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...…are difficulty to sow, control weed and disease, and harvest (Murakami et al., 2009), phytoextraction using Cd-hyperaccumulating rice varieties is advantageous because of the well-established cultivation knowledge and mechanized harvesting systems available (Abe et al., 2011; Clemens et al., 2013)....
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TL;DR: From a survey of 12 countries on four continents, cadmium levels in rice grain were the highest in Bangladesh and Sri Lanka, with both these countries also having high per capita rice intakes.
Abstract: Cereal grains are the dominant source of cadmium in the human diet, with rice being to the fore. Here we explore the effect of geographic, genetic, and processing (milling) factors on rice grain cadmium and rice consumption rates that lead to dietary variance in cadmium intake. From a survey of 12 countries on four continents, cadmium levels in rice grain were the highest in Bangladesh and Sri Lanka, with both these countries also having high per capita rice intakes. For Bangladesh and Sri Lanka, there was high weekly intake of cadmium from rice, leading to intakes deemed unsafe by international and national regulators. While genetic variance, and to a lesser extent milling, provide strategies for reducing cadmium in rice, caution has to be used, as there is environmental regulation as well as genetic regulation of cadmium accumulation within rice grains. For countries that import rice, grain cadmium can be controlled by where that rice is sourced, but for countries with subsistence rice economies that have high levels of cadmium in rice grain, agronomic and breeding strategies are required to lower grain cadmium.
356 citations
References
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TL;DR: It can be anticipated that a considerable proportion of the non-smoking adult population has urinary cadmium concentrations of 0.5 microg/g creatinine or higher in non-exposed areas, and for smokers this proportion is considerably higher, which implies no margin of safety between the point of departure and the exposure levels in the general population.
1,954 citations
TL;DR: This review discusses the molecular mechanisms of toxic metal accumulation in plants and algae, the responses to metal exposure, as well as the understanding of metal tolerance and its evolution.
1,598 citations
TL;DR: The state of the art of the understanding of the physiological, molecular, and genetic basis underlying metal hyperaccumulation and its evolution is described and the future research needs and opportunities are described.
Abstract: During the history of life on Earth, tectonic and climatic change repeatedly generated large territories that were virtually devoid of life and exhibited harsh environmental conditions. The ability of a few specialist pioneer plants to colonize such hostile environments was thus of paramount ecological importance for the continuous maintenance of primary production over time. Yet, we know very little about how extreme traits evolve and function in plants. Recent breakthroughs have given first insights into the molecular basis underlying the complex extreme model trait of metal hyperaccumulation and associated metal hypertolerance. This review gives an introduction into the hyperaccumulator research field and its history; provides an overview of hyperaccumulator germplasm; describes the state of the art of our understanding of the physiological, molecular, and genetic basis underlying metal hyperaccumulation and its evolution; and highlights future research needs and opportunities.
1,067 citations
TL;DR: While plant breeding and agronomic management can minimize soil–plant transfer of Cd, and maximize concentrations of antagonists to Cd assimilation in humans, it remains important that inputs of this metal to soil be minimized.
887 citations
TL;DR: The development of apoplastic barriers to Cd movement to the xylem is described and recent experiments indicating that their maturation is accelerated by high Cd concentrations in their immediate locality are highlighted.
Abstract: This article reviews the responses of plant roots to elevated rhizosphere cadmium (Cd) concentrations. Cadmium enters plants from the soil solution. It traverses the root through symplasmic or apoplasmic pathways before entering the xylem and being translocated to the shoot. Leaf Cd concentrations in excess of 5-10 μg g(-1) dry matter are toxic to most plants, and plants have evolved mechanisms to limit Cd translocation to the shoot. Cadmium movement through the root symplasm is thought to be restricted by the production of phytochelatins and the sequestration of Cd-chelates in vacuoles. Apoplasmic movement of Cd to the xylem can be restricted by the development of the exodermis, endodermis, and other extracellular barriers. Increasing rhizosphere Cd concentrations increase Cd accumulation in the plant, especially in the root. The presence of Cd in the rhizosphere inhibits root elongation and influences root anatomy. Cadmium concentrations are greater in the root apoplasm than in the root symplasm, and tissue Cd concentrations decrease from peripheral to inner root tissues. This article reviews current knowledge of the proteins involved in the transport of Cd across root cell membranes and its detoxification through sequestration in root vacuoles. It describes the development of apoplastic barriers to Cd movement to the xylem and highlights recent experiments indicating that their maturation is accelerated by high Cd concentrations in their immediate locality. It concludes that accelerated maturation of the endodermis in response to local Cd availability is of functional significance in protecting the shoot from excessive Cd loads.
839 citations