Heavy metal (Pb,Zn) uptake and chemical changes in rhizosphere soils of four wetland plants with different radial oxygen loss

Lead and Zn uptake and chemical changes in rhizosphere soils of four emergent-rooted wetland plants;Aneilema bracteatum,Cyperus alternifolius,Ludwigia hyssopifolia and Veronica serpyllifolia were investigated by two experiments：（1） rhizobag filled with ＂clean＂ or metal-contaminated soil for analysis of Pb and Zn in plants and rhizosphere soils;and （2） applied deoxygenated solution for analyzing their rates of radial oxygen loss （ROL）.The results showed that the wetland plants with different ROL rates had significant effects on the mobility and chemical forms of Pb and Zn in rhizosphere under flooded conditions.These effects were varied with different metal elements and metal concentrations in the soils.Lead mobility in rhizosphere of the four plants both in the ＂clean＂ and contaminated soils was decreased,while Zn mobility was increased in the rhizosphere of the ＂clean＂ soil,but decreased in the contaminated soil.Among the four plants,V.serpyllifolia,with the highest ROL,formed the highest degree of Fe plaque on the root surface,immobilized more Zn in Fe plaque,and has the highest effects on the changes of Zn form （EXC-Zn） in rhizosphere under both ＂clean＂ and contaminated soil conditions.These results suggested that ROL of wetland plants could play an important role in Fe plaque formation and mobility and chemical changes of metals in rhizosphere soil under flood conditions.

Identification of rice cultivars with low brown rice mixed cadmium and lead contents and their interactions with the micronutrients iron,zinc,nickel and manganese

Paddy fields in mining areas are usually co-contaminated by a cocktail of mixed toxic heavy metals （e.g., Cd and Pb in Pb/Zn mines）. However, previous studies on rice cultivars screened for effective metal exclusion have mostly focused on individual metals, and have been conducted under pot-trial or hydroponic solution conditions. This study identified rice cultlvars with both low Cd and Pb accumulation under Cd- and Pb-contaminated field conditions, and the interactions of the toxic elements Cd and Pb with the micronutrient elements Fe, Zn, Mn and Ni were also studied. Among 32 rice cultivars tested, there were significant differences in Cd （0.06-0.59 mg/kg） and Pb （0.25-3.15 mg/kg） levels in their brown rice, and similar results were also found for the micronutrient elements. Significant decreases in concentrations of Fe and Mn were detected with increasing Cd concentrations and a significant elevation in Fe, Mn and Ni with increasing Pb concentrations. A similar result was also shown by Cd and Ni. Three cultivars were identified with a combination of low brown rice Cd and Pb, high micronutrient and grain yield （Wufengyou 2168, Tianyou 196 and Guinongzhan）. Present results suggest that it is possible to breed rice eultivars with low mixed toxic element （Cd, Pb） and high micronutrient contents along with high grain yields, thus ensuring food safety and quality.

Interactions Between Arbuscular Mycorrhizae and Plants in Phytoremediation of Metal-Contaminated Soils: A Review

Metal contamination in the environment is a global concern due to its high toxicity to living organisms and its worldwide distribution.The principal goal of this review is to examine the current strategies and technologies for the remediation of metalcontaminated soils by metal-accumulating plants and assess the roles of arbuscular mycorrhizal(AM)fungi in remediation of soils under hyperaccumulator or non-accumulator plants.The use of plants to remove metals from the environment or reduce the toxicity,known as phytoremediation,is an environmentally sustainable and low cost remediation technology.The mechanisms of the use of hyperaccumulator plants for phytoremediation included solubilization of the metal in the soil matrix,the plant uptake of the metal,detoxification/chelation and sequestration,and volatilization.Recently,some ecologists have found that phytoremediation with the aids of mycorrhizae can enhance efciency in the removal of toxic metals.AM fungi can facilitate the survival of their host plants growing on metal-contaminated land by enhancing their nutrient acquisition,protecting them from the metal toxicity,absorbing metals,and also enhancing phytostabilization and phytoextraction.Such information may be useful for developing phytoremediation program at metal-contaminated sites.

Root-Induced Changes of pH, Eh, Fe(Ⅱ) and Fractions of Pb and Zn in Rhizosphere Soils of Four Wetland Plants with Different Radial Oxygen Losses

A rhizobox experiment was conducted to compare iron (Fe) oxidation and changes of pH, redox potential (Eh) and fractions of zinc (Zn) and lead (Pb) in rhizosphere and non-rhizosphere soils of four emergent-rooted wetland plants (Echinodorus macrophyllus, Eleocharis geniculata, Hydrocotyle vulgaris and Veronica serpyllifolia) with different radial oxygen loss (ROL) from roots. The results indicated that all these wetland plants decreased pH and concentration of Fe(Ⅱ) but increased the Eh in the rhizosphere soils. Pb and Zn were transformed from unstable fractions to more stable fractions in the rhizosphere soils, so decreasing their potential metal mobility factors (MF). Among the four plants, E. macrophyllus, with the highest ROL and root biomass, possessed the greatest ability in formation of Fe plaque and in the reduction of heavy metal MFs in the rhizosphere soil. Wetland plants, with higher ROLs and root biomass, may thus be effective in decreasing potential long-term heavy metal bioavailabilities.

Three-dimensional structure of the Chinese Sacbrood bee virus

he RNA of Chinese Sacbrood Bee Virus (CSBV) was purified and used as template to obtain a 1096 bp cDNA fragment by RT-PCR amplification. This DNA fragment was cloned into pGEM-T Easy Vector for sequencing. Analyses of the sequenced CSBV RNA fragment revealed a nucleotide sequence homology of 87.6% and a deduced amino-acid sequence homology of 94.6% with that of the Sacbrood Virus (SBV), indicating that CSBV is a different but highly homologous virus of SBV. The three-dimensional (3D) structure of CSBV was determined at 2.5 nm resolution by using electron cryo-microscopy (cryoEM) and computer reconstruction methods. The 3-D struc-ture showed that the capsid has a T = 1 (or P = 3) icosahedral capsid shell with a smooth surface. There were 12 pentons at its icosahedral vertices (5-fold axes) and 132 holes penetrating the shell. The 3-D structure also revealed densities corresponding to the CSBV genome, suggesting icosa-hedrally-ordered RNA organization, a novel feature not previously reported for any picornaviruses.

Metal accumulation and tolerance in wetland plants

This paper briefly reviews the progress in studies of wetland plants in terms of heavy metal pollution.The current research mainly includes the following areas:(1)metal uptake,translocation,and distributions in wetland plants and toxicological effects on wetland plants,(2)radial oxygen loss(ROL)of wetland plants and its effects on metal mobility in rhizosphere soils,(3)constitutional metal tolerance in wetland plants,and(4)mechanisms of metal tolerance by wetland plants.Although a number of accomplishments have been achieved,many issues still remain unanswered.The future research effort is likely to focus on the ROL of wetland plants affecting metal speciation and bioavailability in rhizosphere soils,and the development of rhizosphere management technologies to facilitate and improve practical applications of phytoremediation of metalpolluted soils.