Plant science: the key to preventing slow cadmium poisoning

doi:10.1016/j.tplants.2012.08.003

Trends in Plant Science

Volume 18, Issue 2, February 2013, Pages 92-99

https://doi.org/10.1016/j.tplants.2012.08.003 Get rights and content

Practically all human populations are environmentally exposed to cadmium (Cd), mostly through plant-derived food. A growing body of epidemiological evidence suggests that there is no margin of safety between current Cd exposure levels and the threshold for adverse health effects and, hence, there is an urgent need to lower human Cd intake. Here we review 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. The emerging molecular understanding of Cd uptake, root retention, root-to-shoot translocation and grain loading will enable the development of low Cd-accumulating crops.

Section snippets

Cd exposure and adverse health effects

Cd has long been recognized as a major health threat to humans. It represents one of the most toxic substances released into the environment 1, 2. Cd is efficiently retained in the human kidney and shows a long biological half-life of 10–30 years, resulting in a cumulative increase in body load with age. Thus, a serious health threat can potentially arise even from low-level chronic exposure. In the 1990s, Cd was classified as a group 1 carcinogen based on data obtained for workers

Cd exposure through plant-derived food

There is a general consensus about the highly dominant role of food intake for environmental Cd exposure 3, 4, whereas drinking water and inhalation of Cd in ambient air are minor sources (Figure 1). Cd intake via food is a function of the Cd concentration of the food and the amount consumed. A recent large-scale analysis of Cd occurrence in food items (almost 180 000 analytical results, grouped in a food classification system) was combined with the EFSA Comprehensive European Food Consumption

Sources of Cd accumulating in plants

Cd has been detected in the majority of food samples analyzed. Concentrations in most food samples vary between 0.01 and 0.05 mg/kg dry weight [4]. Mean values for the food categories ‘cereal products’, ‘vegetables, nuts and pulses’, and ‘potatoes’ in Europe, for example, are 0.023, 0.067, and 0.021 mg/kg, respectively [10], which is consistent with the observation that leaves usually have higher Cd concentrations than seeds [14]. Depending on the level of pollution, much higher values can be

Natural variation in plant Cd accumulation

Cd accumulation levels in plants are strongly influenced by soil parameters such as pH [14], meaning that agronomic practices beyond the scope of this review have the potential to reduce Cd exposure through food [8]. A second approach is to exploit the substantial natural variation in Cd accumulation levels to breed low Cd-accumulating crops. Data on differences between species are rather fragmentary. The relatively efficient accumulation of Cd in tobacco leaves, which accounts for the

Mechanisms of Cd accumulation

There is a longstanding awareness in Japan and other Asian countries of the risks associated with Cd intake in general and the consumption of rice as the main source of Cd exposure. Rice is also the model system for monocot species, which explains why molecular knowledge regarding Cd accumulation is well advanced in rice, progressing beyond analysis of natural variation and identification of QTLs.

OsNramp5 (natural resistance-associated macrophage protein 5) has recently been identified as the

Learning from Cd hyperaccumulators

A recurring theme of Cd accumulation in plants is a strong gradient in Cd concentrations: roots > leaves > seeds and fruits. The work on rice demonstrates that differences in root-to-shoot translocation are key to explaining natural variation in Cd accumulation of aboveground tissues [51]. Metal hyperaccumulating plants are highly efficient in this respect 67, 68. Cd-hyperaccumulators are therefore useful for understanding the pivotal processes responsible for Cd mobility in plants. The study

Perspectives to use knowledge on the mechanisms controlling Cd accumulation

In light of the recent progress in understanding the molecular mechanisms of Cd accumulation, it seems realistic to develop both low Cd-accumulating (to provide food with reduced Cd contamination) and high Cd-accumulating crop cultivars (to extract Cd from soil). The rice QTLs could be used for marker-assisted breeding, which avoids the high costs of Cd phenotyping by Inductively Coupled Plasma Mass Spectrometry. Cdu1, the low Cd-accumulating grain QTL in durum wheat [34], has successfully been

Acknowledgments

Financial support for work on plant Cd accumulation in our laboratories is gratefully acknowledged (DFG 152/CL 9-1, S.C.; ANR 2011 BSV6 004 01, S.T.; FNRS 2.4.583.08, N.V.). COST Action FA905 provided opportunities for scientific exchange. We thank colleagues of the PHIME project for valuable discussions, and Jian Feng Ma (Okayama) and Shimpei Uraguchi (Tokyo) for helpful advice regarding Figure 3.

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Trends in Plant Science

ReviewPlant science: the key to preventing slow cadmium poisoning

Section snippets

Cd exposure and adverse health effects

Cd exposure through plant-derived food

Sources of Cd accumulating in plants

Natural variation in plant Cd accumulation

Mechanisms of Cd accumulation

Learning from Cd hyperaccumulators

Perspectives to use knowledge on the mechanisms controlling Cd accumulation

Acknowledgments

Toxicol. Appl. Pharmacol.

Toxicol. Appl. Pharmacol.

Field Crops Res.

Environ. Res.

Environ. Res.

J. Biol. Chem.

Trends Plant Sci.

Curr. Opin. Plant Biol.

Sci. Total Environ.

Biochimie

Adv. Agron.

Sci. Total Environ.

Field Crops Res.

J. Environ. Sci. (China)

Curr. Opin. Plant Biol.

Curr. Opin. Plant Biol.

Draft Toxicological Profile for Cadmium

Influence of consumption of cadmium-polluted rice or Jinzu River water on occurrence of renal tubular dysfunction and/or Itai-itai disease

Biol. Trace Elem. Res.

Cadmium, environmental exposure, and health outcomes

Environ. Health Perspect.

Cadmium exposure in the population: from health risks to strategies of prevention

Biometals

New perspectives in cadmium toxicity: an introduction

Biometals

Scientific Opinion of the Panel on Contaminants in the Food Chain on a request from the European Commission on cadmium in food

EFSA J.

Cadmium dietary exposure in the European population

EFSA J.

The 20th Australian Total Diet Survey

Nutritional status affects the absorption and whole-body and organ retention of cadmium in rats fed rice-based diets

Environ. Sci. Technol.

Relation between dietary cadmium intake and biomarkers of cadmium exposure in premenopausal women accounting for body iron stores

Environ. Health

Regulation of metal transporters by dietary iron, and the relationship between body iron levels and cadmium uptake

Arch. Toxicol.

Environment: the disappearing nutrient

Nature

Cadmium accumulation in the shoots and roots of 93 weed species

Soil Sci. Plant Nutr.

Evolutionary control of leaf element composition in plants

New Phytol.

Inter- and intraspecific variations of cadmium accumulation of 13 leafy vegetable species in a greenhouse experiment

J. Agric. Food Chem.

Cadmium concentration in grains of Japanese wheat cultivars: genotypic difference and relationship with agronomic characteristics

Plant Prod. Sci.

Cadmium uptake and translocation in seedlings of near isogenic lines of durum wheat that differ in grain cadmium accumulation

BMC Plant Biol.

Targeted mapping of Cdu1, a major locus regulating grain cadmium concentration in durum wheat (Triticum turgidum L. var durum)

Theor. Appl. Genet.

Cadmium loading into potato tubers: the roles of the periderm, xylem and phloem

Plant Cell Environ.

Variation in heavy metal concentrations of potato (Solanum tuberosum L.) cultivars

J. Anim. Plant Sci.

Cadmium in Australian potato tubers and soils

J. Environ. Qual.

Review
Plant science: the key to preventing slow cadmium poisoning