Cell wall modification induced by an arbuscular mycorrhizal fungus enhanced cadmium fixation in rice root.

The chemistry of root cell wall of rice could be changed by inoculation of arbuscular mycorrhizal fungi (AMF). Hydroponic experiments were conducted to investigate the roles of such changes on cadmium (Cd) uptake and distribution in rice. Results showed that inoculation of AM fungus Rhizophagus intraradices (RI) significantly enhanced (p < 0.05) shoot biomass, plant height and root length of rice, and decreased Cd concentration in shoot and root under Cd stress. Moreover, Cd in root was mainly found in pectin and hemicellulose 1 (HC1) components of root cell wall. Inoculation of RI increased the levels of pectin, HC1 and lignin content, accompanied by the increments of L-phenylalanine ammonia-lyase (PAL) and pectin methylesterase (PME) activities. Results of Fourier transform infrared spectroscopy further showed that more hydroxyl and carboxyl groups in root cell wall were observed in mycorrhizal treatment, compared with control. This study demonstrates that cell wall components could be the locations for Cd fixation, which reduced Cd transportation from root to shoot. Inoculation of AMF may remodel root cell wall biosynthesis and affect the characteristics of Cd fixation. The entering and fixing mechanisms should be further studied.

Root cell wall chemistry remodelling enhanced arsenic fixation of a cabbage cultivar.

The low- and high-arsenic (As) transferring cultivars (LTC and HTC) of cabbage showed significant differences in As uptake and distribution. We hypothesise that chemistry of root cell wall matrix plays a critical role. LTC and HTC were treated with As and grown for 60 days. As concentration and distribution at subcellular and cell wall component (pectin, hemicellulose and lignin) levels were determined. Remodelling enzymes (PME and PAL) and functional groups of cell wall were analysed. Results showed that shoot biomass of LTC was not affected by As. Less As was accumulated in shoot of LTC than HTC. LTC allocated more As in root and majority of As was deposited in cell wall. LTC had more hemicellulose 1 (HC1) and lignin, PME and PAL activities. The uronic acid contents of pectin, HC1 or HC2 were all positively (P < 0.05) correlated with As concentrations in each component, respectively. Chemistry of LTC root cell wall was remodelled in terms of changes in porosity, HC and lignin contents, and functional groups, which potentially exerted coupling effects on As entering and deposition. The LTC can restrain As in roots through changing characteristics of root cell wall matrix.

AM fungi increase uptake of Cd and BDE-209 and activities of dismutase and catalase in amaranth (Amaranthus hypochondriacus L.) in two contaminants spiked soil.

Soil co-contaminated with cadmium (Cd) and decabromodiphenyl ether (BDE-209) is a widespread environmental problem, especially in electronic waste contaminated surroundings. Accumulation of Cd and BDE-209 in crops has possibly harmful effects on local human health. In order to assess the potential of arbuscular mycorrhizal (AM) fungi and amaranth (Amaranthus hypochondriacus L.) in remediation of soil co-contaminated with Cd and BDE-209, pot trials were performed to investigate interactive effects of AM fungi, Cd and BDE-209 on growth of amaranth, uptake of Cd and BDE-209, distribution of chemical forms of Cd and activities of antioxidant enzymes in shoots and dissipation of BDE-209 in soil. The present results showed that shoot biomass of non-mycorrhizal plants was significantly inhibited by increasing of Cd addition (5-15 mg kg-1), but were only slightly declined with BDE-209 addition (5 mg kg-1). The interaction of Cd and BDE-209 reduced the proportions of ethanol- and d-H2O-extractable Cd in shoots, consequently alleviated Cd toxicity to plants and enhanced root uptake of Cd and BDE-209. Inoculation of AM fungi resulted in significantly greater shoot biomass as well as higher concentrations of Cd and BDE-209 compared with non-mycorrhizal treatment. Moreover, AM fungi played a beneficial role in relieving oxidative stress on amaranth by increasing the activities of dismutase (SOD) and catalase (CAT) in shoots and significantly improved the dissipation of BDE-209 in soil. The present study suggested that combination of AM fungi and amaranth may be a potential option for remediation of Cd and BDE-209 co-contaminated soils.

Benefit-risk assessment of commonly consumed fish species from South China Sea based on methyl mercury and DHA.

Even though a growing number of reports indicated favorable health effects with fish consumption, kinds of hazardous substances in fish were detected in fish and to be exceeded advisory limitation. Benefit-risk assessment of commonly consumed fish is urgently needed. We conducted fish consumption survey and fish sampling in the coast of South China Sea to assess benefit-risk effect of commonly consumed fish species. For local residents, weekly methyl mercury (MeHg) exposures from commonly consumed fish species ranged from 0.12 to 2.11 µg/kg bw. Apart from Muraenesox cinereus and Acanthopagrus latus, the rest of 92% (23/25) fish species were at low risk of MeHg exposure. Daily docosahexaenoic acid intakes via consuming specific fish were between 42.18 and 1687.04 mg/day. A total of 72% (18/25) fish species could provide 200 mg/day of DNA for local residents. Benefit-risk assessment assuming intelligence quotient (IQ) score model showed net IQ point gains between 1.53 and 5.65 points with consuming various fish species, indicative of large distinction of health benefit from various fish species. This study suggests commonly consumed fish species from China South Sea could bring much more positive effect than negative effect. Species-specific fish should be considered when providing recommendations of fish consumption. Muraenesox cinereus and Acanthopagrus latus should be minded with risk of MeHg exposure in taking large amounts.

Health Risk Assessment for Local Residents from the South China Sea Based on Mercury Concentrations in Marine Fish.

The offshore area of the South China Sea is an important fishing ground in China. We used a food frequency questionnaire to determine marine fish consumption by local residents, and we detected mercury concentrations in commonly consumed marine fish species. In total, 127.9 g/day of the marine fish consumed was identified in 178 local residents. THg and MeHg concentrations in 209 samples of 22 fish species ranged from 11.3 to 215.0 µg/kg wt and 2.0 to 160.0 µg/kg wt, respectively. The mean MeHg exposure from marine fish to local residents was 0.099 µg/kg bw, accounting for 43.0% of the provisional tolerated weekly intake (PTWI) (1.6 µg/kg bw/week), suggesting a low health risk. However, a potentially high health risk (202.2% of PTWI) was identified in those with 97.5% MeHg exposure.