Variation in arsenic accumulation and translocation among wheat cultivars: The relationship between arsenic accumulation, efflux by wheat roots and arsenate tolerance of wheat seedlings
Introduction
Arsenic (As), a noxious, nonessential metalloid, is found in all environment media. Arsenic contamination in the environment is wide-spread due to both natural and anthropogenic reasons [1], [2]. Over 150 million people world-wide are exposed to unsafe levels of As in the drinking water [3]. Increased concentrations of As in the edible part of crops is another principal pathway for human exposure to As [4].
Many studies have focused on As uptake and metabolism in rice during the past few decades [5], [6], [7]. Wheat is the dominant crop which is grown under aerobic conditions in temperate countries and with a total production similar to that of rice [8]. A few studies on As accumulation and translocation in wheat have also been reported in recent years [4], [9], [10]. The results of previous studies have shown that As in wheat grains was mainly existed as inorganic form [9], [10], [11]. Inorganic As, a class I carcinogen, is more toxic than pentavalent methylated As species to animals and human cells [12], [13]. So, it will result in health risk for those people who consume wheat grain with elevated As. Understanding the mechanisms of As metabolism in wheat is important to human health.
Studies have shown that the abilities of arsenic accumulation and translocation by plants depend on plant species and genotypes [14], [15], [16], [17].
Under aerobic condition, the main form of As that plants take up is inorganic arsenate (As(V)) [18]. After taken up by roots, As(V) is rapidly reduced to As(III), then some of As(III) extrude to the external medium [19]. Generally, the efflux of As(III) by rice root was largely and rapidly [20], [21]. Without the strong efflux of As(III), the amount of As accumulation in Holcus lanatus plant tissues would have been 10-fold higher [22]. However, whether As(III) efflux by plant roots is one of the detoxification mechanism is not clear so far. Little is known about the cultivar differences in arsenic accumulation, translocation and As(III) efflux, and their relationship with As tolerance of wheat seedlings.
The objectives of this study are to (1) investigate the differences in As accumulation, translocation, and arsenate tolerance among 57 wheat cultivars, (2) study the variation in As(V) uptake and As(III) efflux among 14 wheat cultivars, (3) analyze the relationship between As uptake, accumulation, efflux by wheat roots and arsenate tolerance of wheat seedlings.
Section snippets
Wheat cultivars
Fifty seven cultivars of winter wheat (Triticum aestivum L.) used in the present study were listed in Table 1.
Plant culture
Wheat seeds were surface sterilized in 3% H2O2 (w/w) for 10-min, rinsed and soaked in distilled water overnight, and then germinated in moist quartz sand for 3-d. Twelve uniform seedlings were selected and transplanted to 2-L 0.5 mmol L−1 CaCl2 solution containing 2 mmol L−1 MOPS-buffer (3-[N -morpholino] propane sulfonic acid). Solution pH was adjusted to 7.0 using HCl or NaOH. All pots
Toxicity of arsenate on wheat seedlings
Arsenate with concentrations of 0–20 μmol L−1 were used to examine the toxic effect of excess As(V) on wheat seedlings (Fig. 1). RRE was reduced by 30.9%, 42.8%, 53.1%, and 50.8%, with As(V) concentrations at 5, 10, 15, and 20 μmol L−1, respectively. RRDW and RSDW of wheat seedlings were decreased by 10.2–24.1% and 1.4–8.1%, respectively, under different As treatments.
Arsenate tolerance of 57 wheat cultivars
The mean membership function value of three indexes were used in the evaluation of As(V) tolerance. Fig. S1 (in Appendix) shows the
Discussion
It is well accepted that the primary sources of dietary As for human are food and drinking water [4], [11], [26], [27]. Although paddy rice is more efficient in accumulating As in the shoots and grains than wheat [28], [29], As concentration in wheat grain could reach 1.22 mg kg−1 when they were grown in soils with elevated As [30]. Different cultivars of wheat possess different abilities to accumulate As in the grains [30]. Therefore, it is very important to investigate the difference of As
Conclusions
The present study showed different wheat cultivars had different capacities on As accumulation, translocation, As(III) efflux and As(V) tolerance after exposure to As(V). Root As concentration in wheat seedlings was related to As(V) uptake, relative As(III) efflux and As transportation from root to shoot. Arsenate tolerant ability of wheat seedling was positively correlated (p < 0.01) with root As concentrations and significantly (p < 0.05) negatively correlated with relative As(III) efflux, but
Acknowledgements
The authors would like to thank Dr. Q. Zhou of Nanjing Agricultural University, PR China for providing wheat seeds. Financial support from the National Natural Science Foundation of China (41201524), the Natural Science Foundation of Jiangsu Province (BK20131322) and the Research Fund for Postgraduate Scientific Research Innovation Project of Jiangsu Province (CXZZ13_0274) are gratefully acknowledged.
References (44)
- et al.
Arsenic transformations in the soil–rhizosphere–plant system: fundamentals and potential application to phytoremediation
J. Biotechnol.
(2002) - et al.
Aquatic arsenic: toxicity, speciation, transformations, and remediation
Environ. Int.
(2009) - et al.
Arsenic in groundwater: a threat to sustainable agriculture in South and South-East Asia
Environ. Int.
(2009) - et al.
Arsenic contamination of the soil–wheat system irrigated with high arsenic groundwater in the Hetao Basin, Inner Mongolia China
Sci. Total. Environ.
(2014) - et al.
The effect of silicon on the uptake and translocation of arsenic in tomato (Solanum lycopersicum L.)
Environ. Exp. Bot.
(2014) - et al.
Effects of oxalate and phosphate on the release of arsenic from contaminated soils and arsenic accumulation in wheat
Chemosphere
(2006) - et al.
The effects of radial oxygen loss on arsenic tolerance and uptake in rice and on its rhizosphere
Environ. Pollut.
(2012) - et al.
Effects of phosphate on arsenate and arsenite sensitivity in two rice (Oryza sativa L.) cultivars of different sensitivity
Environ. Exp. Bot.
(2011) - et al.
Toxicity of arsenate and arsenite on germination, seedling growth and amylolytic activity of wheat
Chemosphere
(2005) - et al.
Differential response of oxidative stress and thiol metabolism in contrasting rice genotypes for arsenic tolerance
Ecotox. Environ. Safe.
(2012)