Accumulation and distribution of arsenic and cadmium in winter wheat (Triticum aestivum L.) at different developmental stages.

Arsenic (As) and cadmium (Cd) are known to be toxic to humans, and elevated concentrations have been documented in food crops worldwide. However, little is known regarding their uptake, translocation, and distribution in wheat plants during plant development. A series of experiments were conducted to investigate the spatial distribution and dynamics of As and Cd in two wheat cultivars (cv. JN12 and JM85; the latter is a low grain Cd accumulator) at different developmental stages. Root concentrations of As decreased by 84%, and those of Cd by 67%, from tillering to maturity. In contrast, As concentrations in the stems increased 3.1-fold. A significant decrease in root As accumulation was observed at the mature stage, whereas root Cd accumulation decreased largely at the elongation stage. The concentrations of Cd in all leaves and As in new leaves increased as plant growth advanced. However, As concentrations in old leaves decreased significantly from grain filling to maturity. In both cultivars, the upward transfer toward younger parts of shoots was greater in the case of Cd than of As. The remobilization of As and Cd from stems and roots differed between the two cultivars. Arsenic concentrations in rachis, glumes, and grain in JM85 were significantly higher than those in JN12, whereas As concentrations in roots and stems did not differ between the cultivars. Grain Cd was significantly higher in JN12 than in JM85, but Cd concentrations in rachis and glumes were similar between the cultivars. The difference in grain Cd concentration between the two cultivars depended on root and stem Cd remobilization and redistribution from rachis to glumes and grain; in contrast, accumulation of As in grain was influenced by As remobilization from the leaves and stem to the spike.

Phytochelatins play key roles for the difference in root arsenic accumulation of different Triticum aestivum cultivars in comparison with arsenate uptake kinetics and reduction.

In the previous studies, we have found that arsenic (As) accumulation in roots of bread wheat (Triticum aestivum L.) seedlings were significantly different among different wheat cultivars, and As(V) tolerant wheat cultivars have much higher capacities of root As accumulation. However, the reason for the difference remains unclear. Four wheat cultivars with high (MM45 and FM8) or low (QF1 and HM29) levels of arsenic (As) accumulation were selected to investigate the relationship between root As(V) uptake kinetics and root As accumulation. MM45 and HM29 were also used to examine As(V) reduction ability and non-protein thiol (cysteine [Cys], glutathione [GSH], and phytochelatins [PCs]) concentrations in wheat seedlings. MM45 had the lowest Michaelis-Menten constant (Km) and maximum influx rate (Vmax). No difference in the Km values was found among the three other cultivars. No difference in As(V) reduction capacity was observed between MM45 and HM29. GSH and PC2 were significantly induced by 10 µM As(V) in roots of wheat seedlings, particularly in MM45. Synthesis of GSH and PCs was completely suppressed in the presence of l-buthionine sulfoximine (BSO), a specific inhibitor of γ-glutamylcysteine synthetase. BSO markedly decreased the As tolerance of wheat seedlings and decreased the accumulation of As in roots, but increased As accumulation in shoots. No significant difference in As concentrations was found between MM45 and HM29 under the BSO treatment. GSH and PCs are the reason why As accumulation and As(V) tolerance differ in roots of different wheat cultivars.

The transportation and accumulation of arsenic, cadmium, and phosphorus in 12 wheat cultivars and their relationships with each other.

Pot experiments were conducted to investigate the difference in arsenic (As), cadmium (Cd), and phosphorus (P) uptake, accumulation, and translocation among 12 wheat cultivars and their relationships with each other in soil "naturally" contaminated with both As and Cd. As, Cd, and P concentrations in wheat grain, straw, and root differed significantly (p<0.05) among the 12 wheat cultivars. The grain As concentration was not correlated with straw and root As, or the total As content in plants, but was significantly (p<0.05) correlated with As translocation factors (TFs), i.e., TFs(Grain/Root) and TFs(Grain/Straw). The grain Cd concentration was positively correlated with the total Cd content and TFs(Grain/Straw). The grain P concentration was positively correlated with straw and root P. Both As and Cd concentrations in wheat grains were correlated with P in wheat straw and grain. Compared with As, Cd was more easily transported to the wheat grain, and the rachis played a key role in ensuring this difference. A significant positive correlation was observed between root As and Cd, but no significant relationship was detected between grain As and Cd concentrations. The lack of a relationship between grain As and Cd suggests the possibility of selecting cultivars in which little As and Cd accumulation occurs in the wheat grain.

Variation in arsenic accumulation and translocation among wheat cultivars: the relationship between arsenic accumulation, efflux by wheat roots and arsenate tolerance of wheat seedlings.

Fifty-seven wheat cultivars were used to investigate the differences in arsenic (As) accumulation, efflux and translocation among wheat cultivars and their relationship with arsenate (As(V)) tolerance under hydroponic condition. The relationship between wheat root As accumulation, As(V) uptake, arsenite (As(III)) efflux and As(V) tolerance of 14 wheat cultivars were also investigated. The results showed there were significant (p<0.001) differences in As(V) tolerance, As accumulation and translocation among 57 wheat cultivars. Arsenate tolerance of wheat seedlings was positively correlated with As(V) uptake (p<0.05), root As concentration (p<0.001), but negatively correlated (p<0.05) with TFs and relative As(III) efflux. No significant correlation between As(III) efflux and As(V) tolerance was found (p=0.442). 56-83% of total As taken up by roots was extruded to nutrient solution. Root As concentration was positively correlated with As(V) uptake (not significant, p=0.100), negatively correlated (p<0.001) with relative As(III) efflux, whereas not significantly correlated (p=0.773) with As(III) efflux. The results indicated that As(V) tolerant wheat cultivars have much higher capacity of root As accumulation. Arsenic detoxification in root cells is important for wheat seedlings under As(V) exposure.

Arsenic, copper, and zinc contamination in soil and wheat during coal mining, with assessment of health risks for the inhabitants of Huaibei, China.

Field studies were conducted to investigate arsenic (As), copper (Cu), and zinc (Zn) contamination in agricultural soils and wheat crops at two areas in Huaibei, China. Area A is in the proximity of Shuoli coal mine. In area B, three coal mines and a coal cleaning plant were distributed. The potential health risk of As, Cu, and Zn exposure to the local inhabitants through consumption of wheat grains was also estimated. The results showed that significantly higher (p<0.05) concentrations of As, Cu, and Zn were found in soils collected from area B than in those from area A. Arsenic concentrations in wheat sampled from area A were negatively correlated with the distance from the coal mine (p<0.001). Concentrations of Cu and Zn in wheat seedlings and grains collected from area B were significantly higher (p<0.05) than in those collected from area A, with the exception of Zn in wheat seedlings. Concentrations of Cu and Zn in most wheat grain samples were above the permissible limits of Cu and Zn in edible plants set by the Food and Agriculture Organization/World Health Organization. The hazard index of aggregate risk through consumption of wheat grains was 2.3-2.4 for rural inhabitants and 1.4-1.5 for urban inhabitants. The average intake of inorganic As for rural inhabitants in Huaibei was above 10 µg day(-1). These findings indicated that the inhabitants around the coal mine are experiencing a significant potential health risk due to the consumption of locally grown wheat.

Effects of elevated CO2 on growth, carbon assimilation, photosynthate accumulation and related enzymes in rice leaves during sink-source transition.

To study the effects of growing rice (Oryza sativa L.) leaves under the treatment of the short-term elevated CO(2) during the period of sink-source transition, several physiological processes such as dynamic changes in photosynthesis, photosynthate accumulation, enzyme activities (sucrose phosphate synthase (SPS), and sucrose synthase (SS)), and their specific gene (sps1 and RSus1) expressions in both mature and developing leaf were measured. Rice seedlings with fully expanded sixth leaf (marked as the source leaf, L6) were kept in elevated (700 micromol/mol) and ambient (350 mol/L) CO(2) until the 7th leaf (marked as the sink leaf, L7) fully expanded. The results demonstrated that elevated CO(2) significantly increased the rate of leaf elongation and biomass accumulation of L7 during the treatment without affecting the growth of L6. However, in both developing and mature leaves, net photosynthetic assimilation rate (A), all kinds of photosynthate contents such as starch, sucrose and hexose, activities of SPS and SS and transcript levels of sps1 and RSus1 were significantly increased under elevated CO(2) condition. Results suggested that the elevated CO(2) had facilitated photosynthate assimilation, and increased photosynthate supplies from the source leaf to the sink leaf, which accelerated the growth and sink-source transition in new developing sink leaves. The mechanisms of SPS regulation by the elevated CO(2) was also discussed.

QTL for yield and its components responded to elevated CO2 in rice (Oryza sativa L.).

FACE (free air carbon dioxide enrichment) technology may provide a means by which the environment around growing plants can be modified to realistically simulate the concentration of atmospheric CO2 in the future. The plant growth and its yield of plant species can be enhanced under FACE. Identification of genomic regions influencing the response of yield and its components to elevated CO2 will be useful for understanding the genetics of active response to changed CO2 environment and developing higher yield cultivars, which will be adapted to future enriched atmospheric CO2 environment. A mapping population of 65 indica (IR24) chromosome segment substitution lines (CSSLs) in japonica (Asominori) background and their parents were used to detect QTLs for yield and its components, e. g. number of fertile tillers per plant (FT), 1000-grain weight (TGW), number of grains per panicle (GP) and grain yield per plant (GY) under FACE (200 micromol CO2/mol above current levels) and current CO2 concentration (Ambient, about 370 micromol CO2/mol) in the field experiment. The results showed that, GY, GP and FT of two parents under FACE were significant greater than that under Ambient. The transgressive segregation of the four traits was observed in the CSSLs population under both FACE and Ambient. A total of 20 QTLs for the four traits were detected on chromosome 1, 2, 4, 6, 7, 9 and 12 with LOD (Log10-likelihood ratio) of QTLs ranging from 2.5 to 5.7. Three QTLs were detected under both FACE and Ambient. However,other QTLs were detected only under one level of CO2, which indicated that these loci were sensitive to CO2 concentration. Additionally, two QTLs qFT12 and qGP4 were found for the QTL x Environment (QE) interaction effects. It is suggested that there is a high possibility to improve the yield of rice under elevated CO2 through marker-assisted selection.