Physiological Aspects of Cadmium and Lead Toxic Effects on Higher Plants

Using the examples of cadmium and lead, the review considers the various toxic effects exerted by these heavy metals. Putative specific and nonspecific mechanisms of the toxic effects of the heavy metals and plant responses are discussed together with the issue of Cd and Pb accumulation in various plant organelles, cells, tissues, and organs. The basic mechanisms providing for plant resistance to excess Cd and Pb are elucidated. These data are used to schematically outline the changes in plant metabolism produced by these heavy metals.     

茶树根细胞壁不同组分对铅的吸附性能及其功能团的傅里叶红外光谱学研究

选择我国重要的经济作物之一茶树(Camellia sinensis L.)为研究对象,考察了茶树根细胞壁中不同多糖组分在吸附铅(Pb)过程中的作用差异以及与其发生交互作用的主要功能团。结果表明,在茶树根细胞壁吸附Pb过程中,绝大多数的Pb(68.42%)是吸附在纤维素以及木质素上;其次是果胶(20%)、半纤维素2类(5.26%);半纤维素1类的贡献可以忽略不计。同时,通过细胞壁不同组分吸附Pb前后的傅立叶红外光谱表征结果得出,在吸附Pb的过程中,果胶中起作用的功能团主要有羟基、羧基;半纤维素1类中起作用的功能团主要是羧基;半纤维素2类中起作用的功能团主要为羟基。     

蛋白核小球藻对Pb(Ⅱ)和Cd(Ⅱ)的生物吸附及其影响因素

藻类吸附作用影响重金属在水生生态系统中的迁移过程及其环境行为。同时,利用藻类吸附能力是修复重金属污染水体和重金属废水处理的一项清洁、廉价和高效的技术。测定了蛋白核小球藻对Pb2+和Cd2+的吸附和脱附动力学,表明吸附是快速表面过程,吸附4 h后基本达到平衡,不易脱附。研究了蛋白核小球藻对Pb2+和Cd2+的吸附热力学,绘制了吸附等温线,并用Langmuir模型进行拟合,相关系数R2分别为0.9906和0.9827,计算得到最大吸附量分别为0.373 mmol Pb/g和0.249 mmolCd/g。考察了pH值、离子强度和温度等环境因素对蛋白核小球藻吸附Pb2+和Cd2+的影响。结果表明,蛋白核小球藻对Pb2+和Cd2+的吸附量在pH值5.0—6.0之间达到最大值,并随着溶液离子强度的增加而降低,随着溶液温度的升高而增加。温度的影响还表明,蛋白核小球藻对Pb2+和Cd2+的吸附是吸热过程。实验还考察了水体环境中普遍存在的溶解性有机质主要成分-富里酸的影响,表明富里酸会抑制蛋白核小球藻对Pb2+和Cd2+的吸附,重金属离子浓度较低时的抑制效果更明显,最大抑制率分别达到了34.2%和34.9%。由于其对重金属的较高吸附量和吸附本身快速完成的特性,蛋白核小球藻有望成为较理想的生物吸附剂,在重金属污染水体的生物修复及废水处理中发挥重要作用。     

Pb和Cd对森林土壤细菌功能多样性及群落结构的影响

重金属的毒性系数（The Toxic Factor,TF）是评价重金属潜在生态风险指数（potential ecological risk index,RI）的关键参数。为了探究基于Hakanson提出的TF值是否适用于重金属对土壤微生物的生态风险评估,以TF值为5和30的铅（Pb）和镉（Cd）构建土壤微宇宙试验,构建不同的RI水平（100、200和400）,通过Biolog-ECO板和高通量测序技术分析了Pb和Cd分别对细菌功能多样性及群落结构的影响。结果表明,对照处理（CK）的细菌丰度、功能多样性（Shannon指数,Simpson指数和McIntosh指数）和基因多样性（ACE和Chao1指数）均大于Pb、Cd污染的土壤,随着RI水平的升高,Pb和Cd污染土壤中细菌的丰度、功能多样性（Shannon指数和McIntosh指数）和基因多样性（Chao1指数和ACE指数）呈下降趋势。相同RI水平下,Pb污染土壤中细菌群落的丰度、平均颜色变化率（AWCD）、功能多样性指数、OTUs数和基因多样性指数均显著大于Cd污染（P<0.05）;6大类碳源利用率及主成分（PCA）分析表明,Pb污染土壤中细菌对糖类和羧酸的利用率均显著大于Cd污染（P<0.05）,在不同RI水平和重金属比例下,碳源利用模式而有所不同。同一RI水平下,相对于Pb污染,Cd污染土壤中变形菌门的相对丰度较为丰富,而绿弯菌门的相对丰度稀少;Pb和Cd污染土壤中慢生根瘤菌属、鞘脂单胞菌属、链霉菌属和norank_f__Roseiflexaceae等不同属细菌相对丰度表现出差异性。上述结果表明Hakanson提出的TF值并不适用于评估重金属Pb和Cd对土壤微生物的潜在生态风险。     

Physiological analyses indicate superoxide dismutase,catalase, and phytochelatins play important roles in Pb tolerance in Eremochloa ophiuroides

Phytoremediation is considered to be a promising approach to restore or stabilize soil contaminated by lead (Pb). Turfgrasses, due to their high biomass yields, are considered to be suitable for use in phytoextraction of soil contaminated with heavy metal. It has been demonstrated that centipedegrass (Eremochloa ophiuroides (Munro) Hack., Poaceae) is a good turfgrass for restore of soil contaminated by Pb. However, the enhanced tolerant mechanisms in metallicolous (M) centipedegrass accessions remain unknown. In this study, we made a comparative study of growth performance, Pb accumulation, antioxidant levels, and phytochelatin concentrations in roots and shoots from M and nonmetallicolous (NM) centipedegrass accessions. Results showed that turf quality and growth rate were less repressed in M accessions than in NM accession. Pb stress caused generation of reactive oxygen species in centipedegrass with relatively lower levels in M accessions. Antioxidant activity analysis indicated that superoxide dismutase and catalase played important roles in Pb tolerance in M accessions. M accessions accumulated more Pb in roots and shoots. Greatly increased phytochelatins and less repressed sulfur contents in roots and shoots of M accessions indicated that they correlated with Pb accumulation and tolerance in centipedegrass.     

Computational analysis of spiro-oxindole inhibitors of the MDM2-p53 interaction: insights and selection of novel inhibitors

Since MDM2 is an inhibitor of the p53 tumor suppressor, disrupting the MDM2-p53 interaction is a promising approach for cancer therapy. Here, we used molecular dynamics simulations followed by free energy decomposition analysis to study conformational changes in MDM2 induced by three known spiro-oxindole inhibitors. Analysis of individual energy terms suggests that van der Waals and electrostatic interactions explain much of the binding affinities of these inhibitors. Binding free energies calculated for the three inhibitors using the molecular mechanics-generalized Born surface area model were consistent with experimental data, suggesting the validity of this approach. Based on this structure-function analysis, several novel spiro-oxindole derivatives were selected and evaluated for their ability to block the MDM2-p53 interaction in vitro. These results suggest that combining in silico and experimental techniques can provide insights into the structure-function relationships of MDM2 inhibitors and guide the rational design of anticancer drugs targeting the MDM2-p53 interaction.     

Experimental Assessment of Using Soluble Humic Substances for Remediation of Heavy Metal Polluted Soils

Since heavy metals are nondegradable and strongly bonded in soils, remediation of heavy metal polluted soils by extraction is difficult and current extraction techniques require harsh chemicals such as ethylenediaminetetraacetic acid (EDTA). However, use of EDTA is environmentally problematic because of costs, persistence, toxicity and deterioration of soil structure. Therefore, the potential of soluble natural humic substances (HS) to extract heavy metals from contaminated soils is tested as an environmentally friendly substitute for EDTA. A strongly polluted, calcareous urban soil (CRC soil) and a moderately polluted agricultural soil (CUP soil) were extracted at neutral pH in batch mode by three HS solutions from beech and Norway spruce litter (Beech-HS and Spruce-HS) and processed cow slurry (Bio-HS), all containing 25 mM dissolved organic carbon (DOC). After 10 extractions with a solution to soil ratio of 5:1 (L/kg), 8% to 39% of the total Cd, Cu, Ni and Pb soil contents, lowest for Ni and highest for Cu/Pb, were extracted. Natural and processed HS samples had comparable capacities to extract the heavy metals. A comparison of 100 mM DOC of Bio-HS and EDTA as extractants for Cu from the CRC soil showed extraction of 67% by EDTA and 41% by Bio-HS, indicating somewhat higher efficiency of EDTA than of HS. Sequential extraction of the CRC soil after Bio-HS and EDTA extraction showed removal of exchangeable, carbonate- and metal oxide-bound Cu but also of some residual Cu. It is therefore concluded that HS appears to be an attractive and promising alternative to EDTA as remediation agent for heavy metal polluted soils provided cheap HS of good quality is easily available.     

Metal uptake by iron-efficient and inefficient oats

Metal uptake by oats depending on plant responses to Fe-deficiency stress was investigated. Coker 227 oats classified as Fe-efficient and TAM 0–312 oats as Fe-inefficient cultivars (Hopkins et al., 1992) were grown either alone or in combination in three sandy soils using a pot experiment. These soils were from a field trial with sludge-borne metals applications leading to an increased metal content. Plant shoots were harvested one month after growth. Because soil pH increased from 5.4 to 6.8, shoot Fe level decreased in the Fe-inefficient TAM 0–312 oats compared to Coker 227 oats when plants were grown alone. In combination, TAM 0–312 oats had a negative impact on the availability of Fe in the Fe-efficient Coker 227 oats. Especially, Coker 227 and TAM 0–312 shoots showed chlorosis in mixed culture with high Zn and Mn content in the soil (soil B). However, Fe content in TAM 0–312 shoots in mixed culture did not increase compared to monoculture in all soils. In metal-contaminated soils, TAM 0–312 oats grown alone obtained less Zn and Cd than Coker 227 oats. Additionally at soil pH 6.8, shoot Ni and Mn levels were also lower in TAM 0–312 oats than in Coker 227 oats. Shoot Zn, Cd, and Ni levels decreased in Coker 227 oats from mixed cultures, and were not different compared to those in TAM 0–312 oats. Cu uptake was similar in all treatments except for the mixed culture in soil B. Coker 227 oats have been found to release a phytosiderophore whereas TAM 0–312 did not (Brown et al., 1991). Results indicated that phytosiderophores may lead to a higher Zn, Cd and Ni supply in the rhizosphere of Coker 227 oats and to higher metal contents in their shoots than in TAM 0–312 oats which did not activate such mechanisms.     

土壤铅和锌对植物根际丛枝菌根真菌分布的影响

从秦岭凤县铅锌污染区4种植物根际共鉴定出球囊霉属(Glomus)丛枝菌根真菌(Arbuscular mycorrhizal ungi,AMF)12种,其中缩球囊霉(G.constrictum)是该区域的优势种;缩球囊霉、副冠球囊霉(G.coronatum)、苏格兰球囊霉(G.caledonium)和聚丛球囊霉(G.aggregatum)对铅锌污染具有较强的耐性,而地球囊霉(G.geospo-rum)、台湾球囊霉(G.formosanum)、地表球囊霉(G.versiforme)和两型球囊霉(G.dimorphicum)对铅锌污染的耐性较弱.相关分析表明,土壤Pb、Zn、速效P浓度和pH较低时,对AMF丰度有一定的促进作用,当Pb、Zn、速效P浓度和pH较高时,对AMF丰度为抑制作用,AMF丰度与高浓度Pb呈极显著负相关,与高浓度速效P呈显著负相关.通径分析表明,Pb是影响秦岭重金属污染区AMF丰度的主要因素,其直接和间接作用都较大,而pH、速效P和Zn主要通过Pb的间接作用来影响AMF丰度.     

Pb污染对马蔺生长、体内重金属元素积累以及叶绿体超微结构的影响

通过土壤单因子Pb胁迫盆栽试验和铅锌尾矿污染土壤掺比试验研究了不同土培条件下Pb对马蔺（Iris lactea var chinensis）生长、体内重金属元素积累以及叶绿体超微结构的影响。结果表明：2种不同土壤Pb胁迫下马蔺株高、根长、叶数以及地上、地下部生物量均随Pb浓度的增加呈先增后降的趋势,其中,土壤单Pb胁迫下,低于500 mg?kg-1Pb胁迫（T1—T3）均增加了马蔺的株高和根长,仅800mg?kg-1高Pb浓度处理时马蔺生物量才出现轻微下降（P＞0.05）;与单一土壤Pb胁迫相比,铅锌尾矿污染土壤掺比试验中铅锌尾矿含量低于一定浓度下对马蔺株高、根长生长同样也具有促进效应,只有100%尾矿污染土壤处理下马蔺地上部和根系生物量下降显著（P＜0.05）。马蔺地上部和根系Pb含量均随土壤中Pb浓度和尾矿含量的增加而增加,800mg?kg-1土壤单Pb胁迫下为340.6、1700.02 mg?kg-1,100%尾矿污染土壤处理下为126.9、1725 mg?kg-1。Pb单独胁迫下马蔺地上部Zn含量随Pb含量的增加逐渐下降, Zn和Pb的吸收表现出一定的拮抗效应;而不同掺比污染土壤胁迫下马蔺地上部和根系Zn积累同Pb一样,均随土壤中Pb、Zn浓度的增加而增加,Zn和Pb的吸收表现为一种协同效应。而2种不同土壤Pb胁迫下马蔺对Cu、Cd的吸收均相对较少。本研究中,800mg?kg-1Pb胁迫处理和50%尾砂土壤胁迫处理下马蔺叶片叶绿体双层被膜及内部基粒和类囊体结构与对照相比变化不大。综上表明,马蔺对重金属Pb有较强的耐受性,具备修复Pb污染土壤的潜在能力。