Assessment of Metal Uptake Capacity of Castor Bean and Mustard for Phytoremediation of Nickel from Contaminated Soil

The effect of increasing level of nickel (Ni) in soil was studied on biomass production, antioxidants, and Ni bioaccumulation and its translocation in castor bean (Ricinus communis) as well as Indian mustard (Brassica juncea) in similar agroclimatic conditions. The plants were exposed to 25, 50, 75, 100, and 150 mg Ni kg^?1 soil for up to 60 days. It was found that R. communis produced higher biomass during the same period at all the contamination levels than B. juncea, and reduction in fresh and dry weights due to the metal contamination in soil was significantly lower in R. communis than in B. juncea. Proline and malondialdehyde in the leaves increased with increase in Ni level in both the species, whereas soluble protein content was found decreased. A correlation between the protein and MDA contents in the leaves and Ni contamination levels revealed that higher r² values for protein and MDA were found in case of B. juncea, which indicates more toxic effects of the metal in this species. R. communis was found to have enhanced proline accumulation (higher correlation value, r²) at different Ni contamination levels. The bioaccumulation of Ni was higher in B. juncea on the basis of the per unit biomass; however, the total metal accumulation per plant was much higher in R. communis than in B. juncea during the same growing periods. The translocation of Ni from roots to shoots was higher in B. juncea at all Ni concentrations. R. communis appeared more tolerant and capable to clean more Ni from the contaminated soil in a given time and also in one crop cycle.     

Organic acid enhanced soil risk element (Cd, Pb and Zn) leaching and secondary bioconcentration in water lettuce (Pistia stratiotes L.) in the rhizofiltration process

The use of natural chelates to enhance risk element mobility combined with rhizofiltration by free floating macrophytes have not been thoroughly studied in recent years. The aim of this study was to investigate the efficiency of organic acids in soil by conducting flushing experiments to enhance the mobility of Cd, Pb, and Zn from soil to solution. In addition, the bioaccumulation of Cd, Pb, and Zn, in water lettuce (Pistia stratiotes L.) will be studied as they affect the biomass in the rhizofiltration process. The results revealed that citric and tartaric acids mobilised the highest amount of all risk elements. In comparison to control, citric acid mobilised 71%, 181%, and 112% of Cd, Pb, and Zn while tartaric acid mobilised 70%, 155%, and 135% of Cd, Pb, and Zn respectively. The bioconcentration factor was approximately 2-5 times higher for juvenile plants than mature plants for all treatments as well as for both parts (leaves and roots). The risk element translocation into aerial parts decreased with increased time. Juvenile and mature plants proved a high accumulation potential and a 3 week growth period was observed as a sufficient time period to remove more than 80% of Cd, Pb, and Zn.     

鬼针草(Bidens pilosa L.)对镉污染农田的修复潜力

为探究富集植物鬼针草对镉(Cd)污染农田土壤的修复潜力,通过野外调查,原土盆栽试验和田间试验,测定鬼针草及其根系土壤Cd含量,计算鬼针草的富集系数和去除率。结果表明,野外调查中不同铅锌矿区生长的鬼针草叶片中Cd含量最大值为53.3 mg/kg。盆栽试验中,低浓度Cd土壤处理(T1),鬼针草地上部Cd的富集系数为4.70,转运系数1.59,大于1。高浓度Cd土壤处理(T2 13.4 mg/kg),其地上部Cd积累量达到43.1 mg/kg,其地上部Cd富集系数为3.51。鬼针草对Cd表现出稳定的积累特性。田间试验小区中,土壤Cd含量均值为2.66 mg/kg,鬼针草中地上部Cd含量均值为10.9 mg/kg,富集系数为4.16,使用鬼针草修复Cd污染土壤每公顷地种植一茬鬼针草的去除率为4.3%—6.2%。使用富集植物鬼针草修复农田Cd污染具有较好的工程应用前景。     

Cadmium tolerance and phytoremediation potential of acacia (Acacia nilotica L.) under salinity stress

In this study, we explored the effect of salinity on cadmium (Cd) tolerance and phytoremediation potential of Acacia nilotica. Two-month-old uniform plants of A. nilotica were grown in pots contaminated with various levels of Cd (0, 5, 10, and 15 mg kg^?1), NaCl (0%, 0.5%, 1.0% (hereafter referred as salinity), and all possible combinations of Cd + salinity for a period of six months. Results showed that shoot and root growth, biomass, tissue water content and chlorophyll (chl a, chl b, and total chl a+b) contents decreased more in response to salinity and combination of Cd + salinity compared to Cd alone. Shoot and root K concentrations significantly decreased with increasing soil Cd levels, whereas Na and Cl concentrations were not affected significantly. Shoot and root Cd concentrations, bioconcentration factor (BCF) and translocation factor (TF) increased with increasing soil Cd and Cd + salinity levels. At low level of salinity (0.5%), shoot and root Cd uptake enhanced, while it decreased at high level of salinity (1.0%). Due to Cd tolerance, high shoot biomass and shoot Cd uptake, this tree species has some potential for phytoremediation of Cd from the metal contaminated saline and nonsaline soils.     

印度芥菜-苜蓿间作对镉胁迫的生态响应

采用温室盆栽试验,研究了重金属镉（Cd）胁迫对印度芥菜和苜蓿间作下的土壤-植物系统的影响,同时对苜蓿的Cd饲用安全进行了评估.结果表明：在土壤Cd含量为0.37～20.37 mg·kg^-1范围内,与单作印度芥菜和苜蓿相比,间作使印度芥菜生物量降低了0.4%～11.8%,而使苜蓿生物量提高了55.3%~70.0%.土壤有效Cd主要受土壤全量Cd和种植植物种类的影响,种植方式对其影响不大.在土壤Cd含量为5.37 mg·kg^-1时,间作印度芥菜地上部Cd含量较单作提高了14.5%,而间作苜蓿地上部Cd含量较单作降低了57.1%;此时,单作和间作苜蓿地上部Cd含量分别为0.21和0.09 mg·kg^-1,均未超过饲料卫生限定标准(0.5 mg·kg^-1).在土壤Cd含量为10.37～20.37 mg·kg^-1范围内,虽然单作和间作苜蓿Cd含量均超过饲料卫生限定标准,但间作种植方式仍然使苜蓿地上部Cd含量较单作降低了2.8%～48.3%,印度芥菜地上部Cd含量也较单作降低了1.1%～48.6%.不论单作还是间作印度芥菜的Cd转运系数都远高于苜蓿.     

Growth and nutrients accumulation potentials of giant reed (Arundo donax L.) in different habitats in Egypt

Arundo donax L. has a high biomass production and a tendency toward community dominance in many habitats and thereby a tolerance to a wide range of environmental conditions. Therefore, the present study investigated the potentiality of A. donax to accumulate nutrients and trace metals in its biomass. Six main habitats (Nile Bank, Drain Bank, Canal Bank, Field Edges, Railways and Roadsides) were recognized. At each habitat, six quadrats (each 1 m²), distributed equally in two sites, were selected for growth measurements (e.g., density, shoot height, diameter, leaf area and biomass), plant and soil analyses. Plants from Nile, Canal and Drain Banks had the highest values of most growth measurements, while those from Railways and Roadsides had the lowest. Canal Bank plants accumulated the highest concentrations of P, Cu and Pb in their leaves; Zn in the stem; and Mg, Cd and Fe in the rhizome. The bioaccumulation factor (BF) of A. donax, for Cd, Fe, Mn and Zn, was greater than 1, while the translocation factor (TF) of most trace metals was less than unity in most habitats. In conclusion, A. donax showed morphological plasticity in response to habitat heterogeneity, and its growth was most vigorous in the riparian habitats. The high BF, as well as the significant positive correlations between trace metals, especially Cd, in soil and plant, renders A. donax a powerful phytoremediator.     

Bioaccumulation and translocation of heavy metals by Plantago major L. grown in contaminated soils under the effect of traffic pollution

The present study was performed at a heavy-traffic affected soil to examine the efficacy of bioaccumulation and translocation potentials of heavy metals by the naturally growing weed Plantago major. Heavy metals were analyzed in soil as well as in plant below- and above-ground parts along different distances from a heavy-traffic highway. All the investigated soil heavy metals, except Cd, varied significantly, while pH and E.C had no significant difference, with increasing distance from the highway. Likewise, there was a significant decrease of heavy metals in plant below- and aboveground parts. In addition, no significant difference between most soil and root heavy metals at 20 and 100 m as well as those at 500 and 750 m distance from the highway. The bioaccumulation factor (BF) of all heavy metals, except Cd and Sr, were less than unity at most distances. However, Cd showed relative BF decline with the distance in contrast to Sr, which increases as distance from the highway increases. On the other hand, the translocation factors (TF) of Cd, Co, Cu, Pb and Zn were higher at the distances far from the highway, while that of Fe, Cr and Sr were higher near the highway. Furthermore, the enrichment factor (EF) showed small variations, among the investigated heavy metals, with varying distances from the pollution source. It was found that soil Fe, Al, Cr, Ni, Sr, V and Zn had significant positive correlation with all investigated heavy metals in P. major roots. The higher TFs of Cd, Fe and Pb in P. major shoots makes it suitable for phytoextraction from soil, while the lower ratios of Al, Mn, V, Co, Ni, Cr, Zn, Cu and Sr make it suitable for their phytostabilization. Therefore, this plant can be used as a bioindicator and biomonitor for traffic related heavy metals.     

矿区分离丛枝菌根真菌对万寿菊吸Cd潜力影响

盆栽试验研究土壤不同施Cd水平(0、5、20、50μg/g)下,接种矿区污染土壤中丛枝菌根真菌对万寿菊根系侵染率、植株生物量及Cd吸收与分配的影响。结果表明:接种丛枝菌根真菌显著提高Cd胁迫下万寿菊的根系侵染率和植株生物量;随着施Cd水平提高,各处理植株Cd浓度显著增加。各施Cd水平下万寿菊地上部Cd吸收量远远高于根系Cd吸收量,在土壤施Cd量达到50μg/g时,接种处理地上部Cd吸收量是根系的3.48倍,对照处理地上部Cd吸收量是根系的1.67倍;同一施Cd水平下接种处理植株Cd吸收量要显著高于对照。总体上,试验条件下污染土壤中分离的丛枝菌根真菌促进了万寿菊对土壤中Cd的吸收,并在一定程度上增加Cd向地上部分的运转,表现出植物提取的应用潜力。     

微生物对植物修复重金属污染土壤的促进效果

以印度芥菜作为超富集植物,通过盆栽试验研究了巨大芽胞杆菌和胶质芽胞杆菌的混合微生物制剂、黑曲霉30177发酵液对植物修复Cd、Pb、Zn污染土壤的作用.结果表明：巨大芽胞杆菌和胶质芽胞杆菌的混合微生物制剂不仅可以促进超富集植物的生长,增强超富集植物对土壤Cd、Pb、Zn的吸收,而且大幅度提高了植物的修复效率,在添加外源可溶性Cd、Pb、Zn的污染土壤上,可分别使印度芥菜提取量(以植物干质量计)提高1.18、1.54和0.85倍,在添加底泥Cd、Pb、Zn污染的土壤上,可分别使印度芥菜提取量提高4.00、0.64和0.65倍,在底泥污染的土壤上的促进效果明显强于外源添加污染的土壤.黑曲霉30177发酵液能显著促进印度芥菜对土壤Cd、Pb、Zn的吸收,在添加外源可溶性Cd、Pb、Zn的污染土壤上,印度芥菜地上部Cd、Pb、Zn的吸收量分别比对照提高了88.82%、129.04%和16.80%;在添加底泥Cd、Pb、Zn污染的土壤上,可分别比对照提高78.95%、113.63%和33.85%;但它可导致印度芥菜生物量的大幅度降低,起不到提高植物修复提取量的效果.经反相高效液相色谱初步分析发现,胶质芽胞杆菌、巨大芽胞杆菌发酵液中含有草酸、柠檬酸等有机酸,有机酸对重金属有一定的溶解作用,从而提高了重金属的生物有效性.     

Arbuscular mycorrhizal contribution to heavy metal uptake by maize (Zea mays L.) in pot culture with contaminated soil

In two pot-culture experiments with maize in a silty loam (P2 soil) contaminated by atmospheric deposition from a metal smelter, root colonization with indigenous or introduced arbuscular mycorrhizal (AM) fungi and their influence on plant metal uptake (Cd, Zn, Cu, Pb, Mn) were investigated. Soil was -irradiated for the nonmycorrhizal control. In experiment 1, nonirradiated soil provided the mycorrhizal treatment, whereas in experiment 2 the irradiated soil was inoculated with spores of a fungal culture from P2 soil or a laboratory reference culture, Glomus mosseae. Light intensity was considerably higher in experiment 2 and resulted in a fourfold higher shoot and tenfold higher root biomass. Under the conditions of experiment 1, biomass was significantly higher and Cd, Cu, Zn and Mn concentrations significantly lower in the mycorrhizal plants than in the nonmycorrhizal plants, suggesting a protection against metal toxicity. In contrast, in experiment 2, biomass did not differ between treatments and only Cu root concentration was decreased with G. mosseae-inoculated plants, whereas Cu shoot concentration was significantly increased with the indigenous P2 fungal culture. The latter achieved a significantly higher root colonization than G. mosseae (31.7 and 19.1%, respectively) suggesting its higher metal tolerance. Zn shoot concentration was higher in both mycorrhizal treatments and Pb concentrations, particularly in the roots, also tended to increase with mycorrhizal colonization. Cd concentrations were not altered between treatments. Cu and Zn, but not Pb and Cd root-shoot translocation increased with mycorrhizal colonization. The results show that the influence of AM on plant metal uptake depends on plant growth conditions, on the fungal partner and on the metal, and cannot be generalized. It is suggested that metal-tolerant mycorrhizal inoculants might be considered for soil reclamation, since under adverse conditions AM may be more important for plant metal resistance. Under the optimized conditions of normal agricultural practice, however, AM colonization even may increase plant metal absorption from polluted soils.     

Efficiency of different types of biochars to mitigate Cd stress and growth of sunflower (Helianthus; L.) in wastewater irrigated agricultural soil

Cadmium contamination in croplands is recognized one of the major threat, seriously affecting soil health and sustainable agriculture around the globe. Cd mobility in wastewater irrigated soils can be curtailed through eco-friendly and cost effective organic soil amendments (biochars) that eventually minimizes its translocation from soil to plant. This study explored the possible effects of various types of plants straw biochar as soil amendments on cadmium (Cd) phytoavailability in wastewater degraded soil and its subsequent accumulation in sunflower tissues. The studied biochars including rice straw (RS), wheat straw (WS), acacia (AC) and sugarcane bagasse (SB) to wastewater irrigated soil containing Cd. Sunflower plant was grown as a test plant and Cd accumulation was recorded in its tissues, antioxidant enzymatic activity chlorophyll contents, plant biomass, yield and soil properties (pH, NPK, OM and Soluble Cd) were also examined. Results revealed that addition of biochar significantly minimized Cd mobility in soil by 53.4%, 44%, 41% and 36% when RS, WS, AC and SB were added at 2% over control. Comparing the control soil, biochar amended soil effectively reduced Cd uptake via plants shoots by 71.7%, 60.6%, 59% and 36.6%, when RS, WS, AC and SB. Among all the biochar, rice husk induced biochar significantly reduced oxidative stress and reduced SOD, POD and CAT activity by 49%, 40.5% and 46.5% respectively over control. In addition, NPK were significantly increased among all the added biochars in soil–plant system as well as improved chlorophyll contents relative to non-bioachar amended soil. Thus, among all the amendments, rice husk and wheat straw biochar performed well and might be considered the suitable approach for sunflower growth in polluted soil.     

Role of Ca2+ on Growth of Brassica campestris L. and B.juncea (L.) Czern & Coss under Na+ Stress

Root and shoot growth of Brassica campestris L.and B.juncea increased significantly(P0.01) with enhanced Ca2+ treatment along with 60 mM NaCl in the root medium.The maximum fresh mass of shoot and root in B.juncea was recorded at 10 mM Ca2+ concentration.The relative growth rate of shoot of both species reached its maximum at 8 mM of Ca2+ concentration.Average rate of Ca2+ intake(Ca) was higher in B.juncea than B.campestris.In B.juncea,the average transport of Ca2+ to shoot increased by 19%,38%,119%,125% and 169% compared with the control.Furthermore specific utilization rate of Ca2+ was higher in B.juncea than B.campestris.In B.campestris it increased by 9%,32%,41% and 59% at 4,6,8,and 10 mM of calcium in comparison to 2 mM Ca2+ treatment.At 4,6,8 and 10 mM of Ca2+ application,the increase in the leaf area ratio was 10,17,23 and 30%,respectively.In the shoot and root portions of B.campestris and B.juncea,Ca2+ had a linear relationship with potassium and sulfur,whereas it was in antagonism with sodium ion.     

表面活性剂对长柔毛委陵菜(Potentilla griffithii var. velutina)修复重金属污染的促进作用

研究了十二烷基苯磺酸钠(SDBS)、十六烷基三甲基溴化铵(CTAB)、聚乙二醇辛基苯基醚(TritonX-100)等不同离子类型的表面活性剂对水稻土中重金属的解吸效果,并采用盆栽实验研究了上述3种表面活性剂对Zn超富集植物长柔毛委陵菜(Potentilla griffithii var. velutina)的生物量、吸收和富集重金属的影响.结果表明:CTAB对水稻土中Zn、Pb、Cd和Cu的解吸效果好于SDBS和TritonX-100,而且3种表面活性剂对各重金属的解吸率大小都为Cd>Zn>Cu>Pb.3种表面活性剂促进长柔毛委陵菜叶、柄和根的生物量增加了0.2～2.5倍,并且长柔毛委陵菜各部位的生物量大小为叶>柄>根.3种表面活性剂都增加了长柔毛委陵菜各部位对Zn、Cd吸收及其叶和柄对Pb、Cu的吸收,同时显著促进Zn、Pb、Cd和Cu从植物根部向地上部转运,从而增加了Zn、Pb、Cd和Cu在长柔毛委陵菜地上部的提取量和分布以及长柔毛委陵菜对Zn、Pb、Cd和Cu的富集能力;因此3种表面活性剂都提高了长柔毛委陵菜修复重金属污染土壤的效率.     

Accumulation, detoxification, and genotoxicity of heavy metals in Indian mustard (Brassica juncea L.)

Plants of Indian mustard (Brassica juncea L.) were exposed to different concentrations (15, 30, 60, 120 microM) of (Cd, Cr, Cu, Pb) for 28 and 56 d for accumulation and detoxification studies. Metal accumulation in roots and shoots were analyzed and it was observed that roots accumulated a significant amount of Cd (1980 microg g(-1) dry weight), Cr (1540 microg g(-1) dry weight), Cu (1995 microg g(-1) dry weight), and Pb (2040 microg g(-1) dry weight) after 56 d of exposure, though in shoot this was 1110, 618, 795, and 409 microg g(-1) dry weight of Cd, Cr, Cu, and Pb, respectively. In order to assess detoxification mechanisms, non-protein thiols (NP-SH), glutathione (GSH) and phytochelatins (PCs) were analyzed in plants. An increase in the quantity of NP-SH (9.55), GSH (8.30), and PCs (1.25) micromol g(-1) FW were found at 15 microM of Cd, however, a gradual decline in quantity was observed from 15 microM of Cd onwards, after 56 d of exposure. For genotoxicity in plants, cytogenetic end-points such as mitotic index (MI), micronucleus formation (MN), mitotic aberrations (MA) and chromosome aberrations (CA) were examined in root meristem cells of B. juncea. Exposure of Cd revealed a significant (P < 0.05) inhibition of MI, induction of MA, CA, and MN in the root tips for 24 h. However, cells examined at 24 h post-exposure showed concentration-wise recovery in all the endpoints. The data revealed that Indian mustard could be used as a potential accumulator of Cd, Cr, Cu, and Pb due to a good tolerance mechanisms provided by combined/concerted action of NP-SH, GSH, and PCs. Also, exposure of Cd can cause genotoxic effects in B. juncea L. through chromosomal mutations, MA, and MN formation.     

Mechanisms of Cadmium Mobility and Accumulation in Indian Mustard

Indian mustard (Brassica juncea L.), a high biomass crop plant, accumulated substantial amounts of cadmium, with bioaccumulation coefficients (concentration of Cd in dry plant tissue/concentration in solution) of up to 1100 in shoots and 6700 in roots at nonphytotoxic concentrations of Cd (0.1 [mu]g/mL) in solution. This was associated with a rapid accumulation of phytochelatins in the root, where the majority of the Cd was coordinated with sulfur ligands, probably as a Cd-S4 complex, as demonstrated by x-ray absorption spectroscopy. In contrast, Cd moving in the xylem sap was coordinated predominantly with oxygen or nitrogen ligands. Cd concentrations in the xylem sap and the rate of Cd accumulation in the leaves displayed similar saturation kinetics, suggesting that the process of Cd transport from solution through the root and into the xylem is mediated by a saturable transport system(s). However, Cd translocation to the shoot appeared to be driven by transpiration, since ABA dramatically reduced Cd accumulation in leaves. Within leaves, Cd was preferentially accumulated in trichomes on the leaf surface, and this may be a possible detoxification mechanism.     

Shoot endophytic plant growth-promoting bacteria reduce cadmium toxicity and enhance switchgrass (<Emphasis Type="Italic">Panicum virgatum</Emphasis> L.) biomass

The aims of the study were to increase the biomass and to alleviate the deleterious effects of cadmium (Cd) in the switchgrass cultivars (Panicum virgatum L.) Alamo and Cave-in-Rock (CIR) under cadmium (Cd) stress using Cd-tolerant shoot endophytic plant growth-promoting bacteria (PGPB). Four shoot endophytic bacterial strains, viz. Bc09, So23, E02, and Oj24, were isolated from the above-ground parts of plants grown in a Cd-polluted soil and were successfully identified by 16S rRNA gene sequencing as Pseudomonas grimontii, Pantoea vagans, Pseudomonas veronii, and Pseudomonas fluorescens, respectively. These four strains were adapted to high CdCl₂ concentrations as they had higher Cd uptake capacities. In addition, they possessed a huge amount of growth regulatory activities e.g., indole acetic acid production, 1-aminocyclopropane-1-carboxylic acid deaminase (ACCD) activity, and phosphate solubilization. Growth particularly the height and biomass of both cultivars increased significantly in response to PGPB inoculation in the 20 µM CdCl₂ stress. The shoot biomass of the PGPB-inoculated Alamo was higher than the CIR under Cd stress. Interestingly, the level of Cd inside PGPB-inoculated plant tissues and the translocation factors were lower compared with the noninoculated Cd control plants. CIR plants exhibited higher Cd content than Alamo plants. Through confocal microscopy, green fluorescence was observed in roots and leaf tissues 2 days after the inoculation of green fluorescent protein (GFP)-labeled bacteria in Alamo, which confirmed the successful colonization of bacteria inside the plant tissues. These shoot endophytic PGPB and switchgrass interactions are useful for the sustainable biomass production of bioenergy crop in a Cd-contaminated environment.     

Cellular evidence of allelopathic interference of benzoic acid to mustard (Brassica juncea L.) seedling growth.

Cellular changes in the roots of mustard (Brassica juncea L.) grown in soil treated with 1.09, 1.46 and 1.83 mg benzoic acid per g soil, a known allelochemical, were analyzed after 7 days. The recoverable concentration of 1.09, 1.46 and 1.8 mg benzoic acid per g soil (measured by high performance liquid chromatography) was 68, 150 and 250 microg benzoic acid per g soil, respectively. The benzoic acid treatments suppressed root growth by 30.5%, 58.8% and 81.1% with increasing concentrations. Transmission electron microscopy studies of roots showed irregular shaped cells arranged in disorganized manner and disruption of cell organelles at cellular level. Root cells showed dissolution of middle lamella (at 68 and 150 microg benzoic acid per g soil) but intact middle lamella with increased wall deposits was observed with 250 microg benzoic acid per g soil. Damage to the mustard root at cellular level was evidenced by changes in cell morphology and internal organization.     

Interaction of silicon and cadmium in <Emphasis Type="Italic">Brassica juncea</Emphasis> and <Emphasis Type="Italic">Brassica napus</Emphasis>

The objective of this study was to determine the effect of silicon (Si) and cadmium (Cd) on root and shoot growth and Cd uptake in two hydroponically cultivated Brassica species (B. juncea (L.) Czern. cv. Vitasso and B. napus L. cv. Atlantic). Both species are potentially usable for phytoextraction. Inhibitory effects of Cd on root elongation were diminished by the impact of Si. Primary roots elongation in the presence of Cd + Si compared with Cd was stronger and the number of lateral roots was lower in B. juncea than in B. napus. Cd content per plant was higher in B. napus roots and shoots compared with B. juncea. Suberin lamellae were formed closer to the root apex in Cd + Si than in Cd treated plants and this effect was stronger in B. napus than in B. juncea. Accelerated maturation of endodermis was associated with reduced Cd uptake. Cd decreased the content of chlorophylls and carotenoids in both species, but Si addition positively influenced the content of photosynthetic pigments which was higher in B. napus than in B. juncea. Si enhanced more substantially translocation of Cd into the shoot of B. napus than of B. juncea. Based on our results B. napus seems to be more suitable for Cd phytoextraction than B. juncea because these plants produce more biomass and accumulate higher amount of Cd. The protective effect of Si on Cd treated Brassica plants could be attributed to more extensive development of suberin lamellae in endodermis.     

Metal Phytoremediation by the Halophyte Limoniastrum monopetalum (L.) Boiss: Two Contrasting Ecotypes

The phytoremediation potential of the halophyte Limoniastrum monopetalum for the removal of Cd and Pb from polluted sites is assessed in this work. Two pot experiments were conducted; the first with wild L. monopetalum grown on soil polluted with Cd and Pb irrigated at different salinities, and the second with commonly cultivated ornamental L. monopetalum grown on soil polluted with Cd irrigated also at different salinities. The data revealed that wild L. monopetalum is a Cd and Pb tolerant plant able to accumulate at least 100 ppm of cadmium in its shoots without showing any significant decrease in terms of biomass production, chlorophyll content or water content suggesting that it could be an accumulator of Cd. Pb above-ground accumulation was kept at low levels with the majority of Pb localized in the roots. On the other hand, contrasting results were obtained for ornamental L. monopetalum which although it was found to be also Cd tolerant, Cd accumulation in its tissues was kept at significantly lower levels especially compared to that of the wild ecotype. In addition for ornamental L. monopetalum salinity did not have a positive effect on Cd accumulation and translocation as observed in the wild type and in other halophytes. Analysis of the salt excretion crystals on the leaf surface confirmed that wild and cultivated ornamental L. monopetalum excrete cadmium and lead through their salt glands as a possible metal detoxification mechanism, although the amount excreted by the ornamental L. monopetalum is significantly less.