[Blocking Effects of Foliar Conditioners on Cadmium, Arsenic, and Lead Accumulation in Wheat Grain in Compound-contaminated Farmland].

Heavy metal contamination of soil has become a hot issue of social concern due to its impact on the safety of agricultural products in recent years. Wheat is one of the most dominant staple food crops worldwide and has become a major source of toxic metals in human diets. Foliar application was considered to be a more efficient and economical method of heavy metal remediation. Field experiments were carried out in Cd-, As-, and Pb-contaminated farmland soils. The effects of foliar conditioners on the accumulation of Cd, As, and Pb in wheat grains were investigated after being sprayed with Zn (0.2% ZnSO4), Mg (0.4% MgSO4), and Mn (0.2% MnSO4) separately and in combination. Thus, the effective foliar conditioners were selected to block the accumulation of Cd, As, and Pb in wheat grains grown in combined heavy metal-contaminated farmland in north China. The results showed that, compared with that in the control, the Cd, As, and Pb contents in wheat grains of the Zn+Mg+Mn foliar treatment were significantly decreased by 18.96%, 23.87%, and 51.31%, respectively, and TFgrain/straw decreased by 14.62%, 27.73%, and 47.70%, respectively. Thus, spraying the compound foliar conditioner of Zn+Mg+Mn could effectively reduce heavy metal accumulation in wheat grains through inhibition translocation of those metals from stem leaves to grain. In addition, the results indicated that Cd and As were mainly distributed at the central endosperm (34.08%-37.08%), whereas Pb was primarily distributed at the pericarp and seed coat (27.78%) of the wheat grain. Compared with that in the control, spraying the compound foliar conditioner of Zn+Mg+Mn extremely decreased Cd and As accumulation in the aleurone layer of the wheat grain by 81.10% and 82.24%, respectively. Except for the pericarp, seed coat, and central endosperm layers, the Pb content in each grain layer was dramatically decreased by 42.85% to 91.15%. There was only a significant negative correlation between heavy metal content and Zn content in the aleurone layer (P2) of wheat flour. In summary, the accumulation of Cd, As, and Pb in wheat grains, especially in the aleurone layer, could be effectively reduced by foliar conditioner application at the jointing, booting, and early filling stages of wheat, separately. Furthermore, besides the foliar treatment, removing wheat bran to reduce Cd contamination in wheat grains is highly recommended to ensure the safe production of wheat.

Foliar uptake screening: A promising strategy for identifying wheat varieties with low lead accumulation.

Lead (Pb) contamination in wheat grain is of great concern, especially in North China. Atmospheric deposition is a major contributor to Pb accumulation in wheat grain. Screening low Pb accumulating wheat varieties has been an effective method for addressing Pb contamination in wheat grain. However, identifying wheat varieties with low Pb accumulation based on foliar uptake of atmospheric Pb has been neglected. Therefore, two field trials with distinct atmospheric Pb deposition were conducted to screen for stable varieties with low Pb accumulation. It was verified that YB700 and CH58, which have high thousand-grain weights and stable low Pb accumulation in field 1 (0.19 and 0.13 mg kg-1) and field 2 (0.17 and 0.20 mg kg-1), respectively, were recommended for cultivation in atmospheric Pb contaminated farmlands in North China. Furthermore, indoor experiments were conducted to investigate Pb uptake by the roots and leaves of different wheat varieties. Our findings indicate that Pb accumulation in different wheat varieties is primarily influenced by foliar Pb uptake rather than root Pb uptake. Interestingly, there was a positive correlation (p < 0.05) between the Pb concentrations in leaves and the stomatal width and trichome length of the adaxial epidermal surface. Additionally, there is a positive correlation (p < 0.01) between the Pb concentration in the wheat grain and trichome length. In conclusion, the screening of wheat varieties with narrower stomatal widths or shorter trichomes based on foliar uptake pathways is an effective strategy for ensuring food safety in areas contaminated by atmospheric Pb.

Transcriptomic mechanisms of reduced PM2.5-Pb retention in the leaves of the low-Pb-accumulation genotype of Chinese cabbage.

Atmospheric fine particulate matter (PM2.5) mainly contributes to Pb accumulation in the edible leaves of Chinese cabbage in North China. It was found that a low-Pb-accumulation (LPA) genotype of Chinese cabbage contained less Pb in leaves than high-Pb-accumulation (HPA) genotype exposed to PM2.5-Pb. However, there are no data on the transcriptional regulatory mechanisms of foliar PM2.5-Pb uptake by Chinese cabbage. The present study investigated the retention of PM2.5-Pb in foliar apoplast and symplasm and the underlying molecular mechanisms of reduced Pb in LPA leaves. It appeared more Pb in apoplast and less Pb in symplasm of LPA leaves, whereas the pattern was opposite in HPA. There were 2646 and 3095 differentially expressed genes (DEGs) in LPA and HPA leaves under PM2.5-Pb stress with clearly genotype-specific function, respectively. Furthermore, mRNA levels of XTH16 regulating cell wall thickening, PME2 and PME6 involved in cell wall remodification were significantly expressed in LPA, but not in HPA. Meanwhile, foliar PM2.5-Pb stress downregulated expression of ZIP1, YSL1, and CNGC3 responsible for Pb influx to cell, and upregulated expression of ABCG36 regulated Pb efflux from symplasm in LPA leaves. These results improve our understanding to the mechanisms underlying foliar Pb uptake from PM2.5-Pb at transcriptomic level.

Mechanism of Pb accumulation in Chinese cabbage leaves: Stomata and trichomes regulate foliar uptake of Pb in atmospheric PM2.5.

Chinese cabbage (Brassica rapa ssp. pekinensis) is one of the most popular and frequently consumed leafy vegetables. It was found that atmospheric PM2.5-Pb contributes to Pb accumulation in the edible leaves of Chinese cabbage via stomata in North China during haze seasons with high concentrations of fine particulate matter in autumn and winter. However, it is unclear whether both stomata and trichomes co-regulate foliar transfer of PM2.5-Pb from atmospheric deposition to the leaf of Chinese cabbage genotypes with trichomes. Field and hydroponic experiments were conducted to investigate the effects of foliar uptake of PM2.5-Pb on Pb accumulation in leaves using two genotypes of Chinese cabbage, one without trichomes and one with trichomes. It was verified that open stoma is a prominent pathway of foliar PM2.5-Pb transfer in the short-term exposure for 6 h, contributing 74.5% of Pb accumulation in leaves, whereas Pb concentrations in the leaves of with-trichome genotype in the rosette stage were 6.52- and 1.04-fold higher than that of without-trichome genotype in greenhouse and open field, respectively, which suggests that stomata and trichomes co-regulate foliar Pb uptake of from atmospheric PM2.5. Moreover, subcellular Pb in the leaves was distributed in the following order of cytoplasm (53.8%) > cell wall (38.5%)> organelle (7.8%), as confirmed through high-resolution secondary ion mass spectrometry (NanoSIMS). The Leadmium™ Green AM dye manifested that Pb in PM2.5 entered cellular space of trichomes and accumulated in the basal compartment, enhancing foliar Pb uptake in the edible leaves of cabbage. The results of these experiments are evidence that both stomata and trichomes are important pathways in the regulation of foliar Pb uptake and translocation in Chinese cabbage.

[Mechanisms of copper uptake by submerged plant Hydrilla verticillata ( L. F. ) royle and Myriophyllum spicatum L].

Cultivation experiments, including short-term copper uptake kinetics, uptake kinetics of Cu by different subcellular fractions and efflux of Cu, were carried out to investigate mechanisms of copper uptake by two species of submerged macrophyte, Hydrilla verticillata (L. f. ) Royle and Myriophyllum spicatum L. The results showed that: (1) Both H. verticillata and M. spicatum showed high influx rates for copper ions with no statistically significant differences [ Vmax (DW) is 2 micromol. (g min) - 1] ; (2) Both leaf and stem Cu concentrations of two strains of plants showed sharp increase with the external medium, and the equilibrium was reached for about 12 h after being exposed to solution with 2 micromol L-1 Cu. Leaves of these two plants accumulated much higher concentrations of Cu than stems. Furthermore, Cu in leaves concentrated predominantly in cell walls ( > 60% ) , followed by soluble and organell fractions; (3) Copper accumulated in cell wall of H. verticillata leaf was considerably higher than that of M. spicatum, and Cu concentrated in intracellular fractions of leaves showed no statistically significant difference between these two plants. Moreover, ability of Cu accumulation and efflux by H. verticillata was higher than that by M. spicatum.

Arsenic speciation in Chinese Herbal Medicines and human health implication for inorganic arsenic.

Rice and drinking water are recognized as the dominant sources of arsenic (As) for human intake, while little is known about As accumulation and speciation in Chinese Herbal Medicines (CHMs), which have been available for many hundreds of years for the treatment of diseases in both eastern and western cultures. Inorganic arsenic was the predominant species in all of CHMs samples. The levels of inorganic arsenic in CHMs from fields and markets or pharmacies ranged from 63 to 550 ng/g with a mean of 208 ng/g and 94 to 8683 ng/g with a mean of 1092 ng/g, respectively. The highest concentration was found in the Chrysanthemum from pharmacies. It indicates that the risk of inorganic As in CHMs to human health is higher in medicines from markets or pharmacies than that collected directly from fields. Some CHMs may make a considerable contribution to the human intake of inorganic arsenic.

[Effects of arsenic from soil and irrigation-water on As accumulation on the root surfaces and in mature rice plants (Oryza sativa L.)].

A compartmented soil-glass bead culture system was used to investigate characteristics of arsenic accumulation in iron plaque and in mature rice plants irrigated using water with arsenic in greenhouse. Arsenic was supplied as a solution of Na3AsO4 * 12H2O at the following stages: tillering, stem elongation, booting, flowering and grain filling. The whole plant was separated into four parts and As concentrations were analyzed in DCB (dithionite-citrate-bicarbonate)-extraction, root, straw, rice husk and grain respectively. The results show that irrigation-water with arsenic has no significant effect on biomass of straw and grain. Arsenic concentrations are distributed in different components of mature rice with the ranking of iron plaque > root > straw > husk > grain. Arsenic in straw and grain just derive from soil in control, and derive from soil and irrigation-water in arsenic treatment. About 76.5% and 71.0% of total arsenic in rice straw are from soil for lines of YY-1 and 94D-64 respectively. There is no significant difference between two lines. However, about 33.6% of total arsenic in grain of YY-1 comes from irrigation-water with arsenic, and only 15.2% of total arsenic in grain of 94D1-64 is from irrigation-water with arsenic. There is a significant difference between YY-1 and 94D-64. Arsenic concentrations in rice grain are lower than the food safety limitation in China (0.7 mg x kg(-1)).