Non-tolerant Populations Research Articles

Comparison and Characterization of a Cell Wall Invertase Promoter from Cu-Tolerant and Non-Tolerant Populations of Elsholtzia haichowensis.

Cell wall invertase (CWIN) activity and the expression of the corresponding gene were previously observed to be significantly elevated in a Cu-tolerant population of Elsholtzia haichowensis relative to a non-tolerant population under copper stress. To understand the differences in CWIN gene regulation between the two populations, their CWIN promoter β-glucuronidase (GUS) reporter vectors were constructed. GUS activity was measured in transgenic Arabidopsis in response to copper, sugar, and phytohormone treatments. Under the copper treatment, only the activity of the CWIN promoter from the Cu-tolerant population was slightly increased. Glucose and fructose significantly induced the activity of CWIN promoters from both populations. Among the phytohormone treatments, only salicylic acid induced significantly higher (p < 0.05) activity of the Cu-tolerant CWIN promoter relative to the non-tolerant promoters. Analysis of 5′-deletion constructs revealed that a 270-bp promoter fragment was required for SA induction of the promoter from the Cu-tolerant population. Comparison of this region in the two CWIN promoters revealed that it had 10 mutation sites and contained CAAT-box and W-box cis-elements in the Cu-tolerant promoter only. This work provides insights into the regulatory role of SA in CWIN gene expression and offers an explanation for differences in CWIN expression between E. haichowensis populations.

Comparative Contribution of СО2/Н2О Exchange Components to the Process of Adaptation to Drought in Xero-Halophytes from the Family Chenopodiaceae with Different Types of Photosynthesis

Components of СО2/Н2О exchange (rates of apparent photosynthesis, transpiration, and dark respiration), as well as efficiency of photosystem I, growth rate, and proline content, were investigated in plants of the С3 species (Atriplex verrucifera M. Bieb), two populations of the С4 species (A. tatarica L.), and two populations of the intermediate С3–С4 species (Sedobassia sedoides (Pall.) Freitag & G. Kadereit), family Chenopodiaceae, in the course of adaptation to PEG-induced moderate osmotic stress (–0.4…–0.5 MPa). Two taken СО2 concentrations (400 and 200 ppm) enabled the examination of stomatal and metabolic contribution to the formation of the mechanisms of drought tolerance and estimate sensitivity of stomata. Under moderate water deficit, the С3 species showed drought tolerance and succulence and was notable for insensitive stomata. Examination of growth characteristics made it possible to reveal differences in productivity and tolerance between populations of the С4 and С3–С4 species. In spite of a different nature of carbon-concentrating mechanism (aspartate in С4 and photorespiratory in С3–С4), populations tolerant to water deficiency shared common features: less sensitive stomata and operation of the mechanism stabilizing water balance of the leaf cells probably due to proline and cyclic transport of electrons. Realization of such a strategy maintains coordination among parameters of СО2/Н2О exchange, which ensures a lower variability of dark respiration and a greater tolerance of plants to moderate osmotic stress. In nontolerant populations, adaptation mainly depends on stomatal closure, which probably results in upsetting the balance among parameters of СО2/Н2О exchange.

Strategies for cadmium detoxification in the white shrimp Palaemon argentinus from clean and polluted field locations

In this study, we investigated the metal handling capacity of non-tolerant and tolerant populations of Palaemon argentinus to cadmium (Cd), through evaluating of the main mechanisms of metal detoxification, metallothioneins (MT) and metal-rich granules (MRG), to probe that the presence of MRG in the second population is responsible of that condition. The tolerant population were exposed to 3.06 and 12.26 μg Cd·L−1, while the non-tolerant shrimp were exposed to 3.06 μg Cd·L−1. Each experiment involved the exposure during 3, 7, 10 and 15 days and, the depuration during 7, 14, 21 and 28 days, for which shrimp were transferred to clean water. The range values of MT concentrations for non-tolerant shrimp were: 12.24–23.91 μg g (w.w), while for tolerant shrimp were: 8.75–16.85 μg g (w.w); MRG levels were: 0.12–0.57 μg g (w.w) and 0.3–2.1 μg g (w.w), respectively. The results showed different strategies for Cd detoxification: the induction of MT was the main pathway in the non-tolerant population, while the formation of Cd-MRG was the main mechanism for tolerant shrimp. These differences could be related to the environmental history and the health status of each populations.

Pharmacokinetics and safety of fentanyl sublingual spray and fentanyl citrate intravenous: a single ascending dose study in opioid-naïve healthy volunteers

Objective: Fentanyl sublingual spray offers rapid pain relief in opioid-tolerant cancer patients, and may be useful in acute or post-operative pain. Both opioid-naïve and non-tolerant patients are likely to receive opioids in these settings. Understanding the relationship between systemic exposure of fentanyl sublingual spray and effects on respiratory function in opioid-naïve or non-tolerant populations is important to ensure patient safety. This study evaluated single-dose fentanyl sublingual spray in opioid-naïve participants.Research design: Participants were randomized to receive single-dose fentanyl sublingual spray (100, 200, 400, 600, 800 mcg) or fentanyl citrate IV in one of five cohorts. Dosing occurred following a 10-h fast, with fasting continuing for 4 h post-dose. Dose proportionality was assessed using analysis of variance and linear regression techniques. PK assessments and safety monitoring were performed through 24 h post-dose. Safety assessments, including adverse event (AE) monitoring, occurred from dosing through Day 7.Results: Fifty participants (19−53 years) received fentanyl sublingual spray or fentanyl citrate IV. Mean maximum plasma concentrations were reached between 0.27–0.60 h post-dose for fentanyl sublingual spray. Peak (Cmax) and total (AUC0–t, AUC0–∞) fentanyl exposures increased in a linear, but more than dose-proportional manner, with higher doses. The most common AEs were somnolence, nausea, and vomiting. All AEs were mild or moderate in severity. Doses at 400, 600, and 800 mcg were associated with nausea and vomiting, requiring pharmacologic intervention. Hypoxia episodes requiring nasal cannula oxygenation were observed with 600mcg and 800mcg doses.Conclusions: Overall, single-dose fentanyl sublingual spray (100–800 mcg) was generally well tolerated, with greater incidences of AEs (e.g. nausea, vomiting, hypoxia) at higher doses. Doses up to 200 mcg may be safely administered to healthy opioid-naïve individuals with routine monitoring; doses between 400–800 mcg may be administered in settings with nasal cannula oxygenation.

Transcript analysis in two alfalfa salt tolerance selected breeding populations relative to a non-tolerant population.

With the growing limitations on arable land, alfalfa (a widely cultivated, low-input forage) is now being selected to extend cultivation into saline lands for low-cost biofeedstock purposes. Here, minerals and transcriptome profiles were compared between two new salinity-tolerant North American alfalfa breeding populations and a more salinity-sensitive western Canadian alfalfa population grown under hydroponic saline conditions. All three populations accumulated two-fold higher sodium in roots than shoots as a function of increased electrical conductivity. At least 50% of differentially expressed genes (p < 0.05) were down-regulated in the salt-sensitive population growing under high salinity, while expression remained unchanged in the saline-tolerant populations. In particular, most reduction in transcript levels in the salt-sensitive population was observed in genes specifying cell wall structural components, lipids, secondary metabolism, auxin and ethylene hormones, development, transport, signalling, heat shock, proteolysis, pathogenesis-response, abiotic stress, RNA processing, and protein metabolism. Transcript diversity for transcription factors, protein modification, and protein degradation genes was also more strongly affected in salt-tolerant CW064027 than in salt-tolerant Bridgeview and salt-sensitive Rangelander, while both saline-tolerant populations showed more substantial up-regulation in redox-related genes and B-ZIP transcripts. The report highlights the first use of bulked genotypes as replicated samples to compare the transcriptomes of obligate out-cross breeding populations in alfalfa.

Genetic variation and selfing rate in Lychnis flos-cuculi along an industrial pollution gradient.

We studied nine populations of a meadow mixed-mating plant Lychnis flos-cuculi growing in a gradient of copper smelter emissions. We hypothesize that metal tolerant populations in the polluted areas have experienced a loss of genetic variation and are more selfing than the populations from the unpolluted areas. One hundred and thirty-five parental plants and 1059 offspring were genotyped with six microsatellite markers. Selfing rates were assessed manually, with Rmes, Mltr and Colony2. Soil toxicity, population density and pollinators' activity were estimated in the studied areas. Populations from the heavily polluted area have experienced a strong founder effect. However, at present, they are characterized by high densities. A recent genetic explosion was registered for the population from the most polluted site, probably due to forest thinning under pollution effects. Selfing rates estimated with different approaches agreed well only for populations with high genetic variation; they comprised 0-0.23 and were similar between polluted and clean areas. Self-fertilization in L. flos-cuculi hardly represents a mechanism for the fixation of advantageous alleles and a barrier for gene flow from non-tolerant populations. The employment of different methods of selfing rate estimation in populations with low genetic variation appears to be necessary, though not a guarantee of reliable conclusions.

Heterologous expression and comparative characterization of vacuolar invertases from Cu-tolerant and non-tolerant populations of Elsholtzia haichowensis.

Vacuolar invertases (VINs) from Cu-tolerant and non-tolerant populations of Elsholtzia haichowensis have similar enzyme properties, and the enzyme protein divergences contribute little to the varied VIN activities between the contrasting populations. In our previous studies of Elsholtzia haichowensis, vacuolar invertase (VIN) activity in roots of a Cu-tolerant population was found to be significantly higher than that of a non-tolerant population under Cu stress. Divergences of amino acid residues in a sucrose-binding box and other regions of the VINs were detected. To test whether the amino acid divergences influence the enzyme properties of VINs, and thus are relevant to the differences in enzyme activities between the contrasting populations of E. haichowensis, two VIN genes from the Cu-tolerant population (EhCvINV) and non-tolerant population (EhNvINV) were heterologously expressed in Pichia pastoris, and the enzyme properties of the recombinants were characterized and compared. Both of the recombinant enzymes showed temperature optima of 70°C and pH optima of 4.5-5.5. Copper as well as other heavy metals caused almost the same inhibition to EhNvINV and EhCvINV. No statistically significant differences were observed between EhNvINV and EhCvINV in K m and k cat values for sucrose. The results provided evidence that the observed residue divergences had little influence on the enzyme properties of VIN in E. haichowensis, and the varied VIN activities between the contrasting populations under Cu stress were not relevant to the amino acid divergences in the proteins. Also, some other possible reasons accounting for this difference in invertase activities were discussed, such as up-regulation of expression of the EhCvINV gene under Cu stress, as Cu tolerance mechanisms in Cu-mine plants.

Heavy metal tolerance of Cardaminopsis halleri (L.) Hayek populations in the Polish Tatra Mts.

Nine populations of &lt;em&gt;Caradaminopsis halleri&lt;/em&gt; growing on old mine spoil hillocks in the Tatra Mts. were studied. Five of the plant populations showed an increased content of zinc, copper and lead in shoots, in correlation with a higher contents of these elements in soil. Laboratory tests revealed the highest index of zinc-tolerance for these populations. In field zinc-tolerant populations produce stunted individuals with a decreased, by more than a half, biomass as compared with non-tolerant populations.

Methylmercury tolerance is associated with the humoral stress factor gene Turandot A

Methylmercury (MeHg) is an environmental neurotoxicant that targets the developing nervous system. In an effort to understand mechanisms of MeHg toxicity we have identified candidate genes that confer tolerance to MeHg using a Drosophila model. Whole genome transcript profiling of developing larval brains of MeHg-tolerant and non-tolerant flies has identified Turandot A (TotA) as a potential MeHg tolerance gene. TotA is a secreted humoral stress response factor in Drosophila that is a direct target of conserved innate immunity signaling pathways. Here we characterize TotA expression in newly generated isogenic lines (isolines) of flies derived from our previously established MeHg-tolerant and non-tolerant populations. TotA mRNA transcript and protein expression is seen to be higher in the tolerant isolines than the non-tolerant lines. Elevated TotA expression in the tolerant lines was seen to span all the larval developmental stages pointing toward a difference in the TotA gene regulation between the MeHg tolerant and non-tolerant strains. We show that TotA is most highly expressed in the fat body (liver equivalent) and is selectively upregulated in the fat body of tolerant flies relative to brain and gut tissues. Fat body-specific transgenic expression of TotA invokes MeHg tolerance as seen by enhanced development of flies reared on MeHg food. In addition, cell based assays show that high TotA expressing C6 cells are more tolerant to MeHg than the low TotA expressing S2 cells. Knockdown of TotA in the C6 cells trends toward a reduction in MeHg tolerance. Identification of TotA as a MeHg tolerance gene suggests a role for conserved cytokine/immune signaling pathways in modulating MeHg toxicity.

Microbial community responses to bioremediation treatments for the mitigation of low-dose anthracene in marine coastal sediments of Bizerte lagoon (Tunisia)

The main goals of this study were to investigate (1) the behavior of microbial communities in response to low-dose bioavailable anthracene addition in lightly contaminated sediment from Bizerte Lagoon and (2) the effects of bioremediation treatments on microbial biomass, activity, and community structure. Sediment microcosms amended with 1 ppm anthracene were incubated in triplicate during 30 days. Biostimulation (addition of nitrogen and phosphorus fertilizer) and bioaugmentation (inoculation of a hydrocarbonoclastic bacterium) were used as bioremediation treatments. Bacterial biomass was estimated using flow cytometry. Sediment oxygen consumption was measured with oxygen microelectrodes. Bacterial community structure was assessed by molecular fingerprints (terminal restriction fragment length polymorphism; T-RFLP) analysis. Anthracene contamination resulted in a significant reduction of bacterial abundance with an impact on cell integrity. Concomitantly, sediment oxygen consumption was strongly inhibited. Correspondence analysis on T-RFLP data indicated that bacterial community structures from anthracene-contaminated microcosms were different from that of the control. Interestingly, the changes observed in microbial biomass, structure, and activities as a result of anthracene contamination were not alleviated even with the use of biostimulation and combination of biostimulation and bioaugmentation strategy for anthracene bioremediation. Nevertheless, both treatment methods resulted in different community structures relative to the contaminated and control microcosms with the appearance of distinct populations. Anthracene spiking severely affected microbial communities, suggesting dominance of nontolerant populations in this lightly-contaminated sediment. Although biostimulation and/or bioaugmentation treatments did not alleviate the anthracene toxic effects, the changes observed in microbial population and structure suggest that the proposed treatments might be promising to promote bacterial growth. Further works are still required to propose a more efficient strategy to stimulate biodegradation that takes into account the complex interactions between species for resource access.

Strain crossing to transfer germination and seedling salt tolerance in alfalfa (Medicago sativa)

This study was conducted to evaluate the potential of strain crossing, transferring seedling salt tolerance into elite cultivars of alfalfa (Medicago sativa L.) without additional selection. Alfalfa cultivars (Mesilla, Moapa 69 and CUF 101) and two donor populations ('AZ-GERM SALT-II' (AZ-GS-II) and AZ-GS-EM) were used in this study. The experiment was conducted during season 2005 at the College of Food and Agriculture Sciences, King Saud University, Experimental Research Station, at Deirab near Riyadh (24oN,46oE), Saudi Arabia. Six strain crosses were produced between the two donor populations and three alfalfa cultivars. The performance of strain crosses for salt tolerance at germination (250 mM NaCl) was between 7.0 and 52.4% higher than the non-tolerant parental population. Seedling emergence was uniformly high for all populations with non-saline irrigation in the glasshouse (78 to 90%) and no significant differences in emergence percentage were observed between parental or strain-cross populations. The ratio of performance with saline irrigation to that under non-saline conditions, of strain crosses averaged 10.6% greater than that of the non-tolerant population. Relatively little variation in single-plant forage yield was observed among populations in either irrigation regime. With saline irrigation, significant low-parent heterosis for survival (+33.2%) was observed, only for the strain cross whose parents differed significantly in survival (AZ-GS-II X CUF 101). These results indicate that strain crossing could be used to achieve a rapid improvement in seedling emergence under salt stress in alfalfa. Strain crossing did not have a consistent effect on seedling survival or forage yield under salt stress (100 mM NaCl). Key words: Lucerne, forage crop, salt tolerance.

Adaptation to high light irradiances enhances the photosynthetic Cu2+ resistance in Cu2+ tolerant and non-tolerant populations of the brown macroalgae Fucus serratus

The relationship between light acclimation and Cu2+ tolerance was studied in two populations of Fucus serratus known to be naturally non-tolerant and tolerant to Cu2+. Acclimation to high irradiances increased the photosynthetic tolerance to Cu2+. The xanthophyll cycle was apparently not involved in protecting the photosynthetic apparatus against Cu2+ toxicity, as results showed that Cu2+ did not induce dynamic photoinhibition. The higher photosynthetic Cu2+ resistance of high light algae did not result in increased growth. The excess energy acquired by high light-adapted algae appeared to be utilized in Cu2+ defense mechanisms in the Cu2+ non-tolerant population. The polyphenol content of the algae was reciprocal to the CuT content, suggesting that polyphenol may be the primary Cu2+ defense of non-tolerant low light algae, acting through secretion and extracellular chelating of Cu2+, while the compounds do not seem to be involved in the primary Cu2+ tolerance mechanism in Cu2+ tolerant algae.

Development of eight polymorphic microsatellites for a Zn/Cd hyperaccumulator Sedum alfredii Hance (Crassulaceae)

Sedum alfredii is a Zn/Cd hyperaccumulator distributed in East Asia. A total of eight polymorphic microsatellite markers were developed. These loci were screened in 25 individuals from one heavy metal-tolerant population and one nontolerant population, respectively. The average allele number of these markers was 5.25 per locus, ranging from two to nine. Population-specific alleles were found at each locus. The observed and expected heterozygosities ranged from 0.000 to 0.640 and from 0.451 to 0.819. Significant deviation from Hardy-Weinberg equilibrium was detected at both the species and the population level. No significant linkage disequilibrium was detected at population level.

Effect of Cu stress on the invertase activity and root growth in two populations of Rumex dentatus L. with different Cu tolerance

There has been no study on key enzymes in sucrose cleavage in metallophyte plants so far, which may be crucial for the plants' root growth and heavy metal tolerance maintenance. Acid invertases are rate-limiting enzymes in sucrose metabolism. Here, we tested the hypothesis that the roots of copper-tolerant plants should manifest a higher activity of acid invertases than nontolerant plants both for supporting growth and for their maintaining tolerance under Cu stress. Two populations of Rumex dentatus L., one from an ancient waste heap at a Cu mine (Cu-tolerant population), and the other from a noncontaminated site (Cu nontolerant population), were used in the experiments. The seedlings of Rumex dentatus L. were exposed to 0, 10, and 40 microM CuCl(2) for 14 days. Cu exposure had a stronger inhibition on root growth and thus resulted in a lower root/shoot ratio in the plants of nontolerant population compared with the Cu-tolerant population. Cu exposure showed a stronger inhibition of acid invertase activity of Cu nontolerant plants than Cu tolerant plants, whereas neutral/alkaline invertase was insensitive to Cu. A positive correlation between the activity of acid invertases and the root growth and root/shoot ratio was observed. The results suggested that the higher activities in acid invertases of Cu-tolerant population might at least partly associate with the plants' Cu tolerance, and their higher activities in acid invertases in turn played an role in maintenance of the Cu tolerance by supplying carbon and energy for tolerance mechanisms.

Effect of fluoride pollution on genetic variability of Larix gmelinii (Pinaceae) in East Siberia

The genetic variability of four natural populations of Larix gmelinii from East Siberia was determined and compared by RAPD analysis. Comparison of the RAPD profiles provided an estimation of variability in 193 RAPD fragments. More than 89% of these fragments were found to be polymorphic. The main genetic variability parameters of the two populations from Central Yakutia, a region free of fluoride pollution, had considerably higher values than those from East Transbaikalia, a region potentially affected by fluoride pollution (FLU, near a fluorite quarry growing on soils with a high natural content of fluorides). AMOVA revealed that 72.94% of the variation was within populations, while only 7.05% of the variation was between populations within geographical regions. The genetic diversity of the FLU fluoride-tolerant population was the lowest, but only slightly lower than that of a fluoride non-tolerant population from Chita, 50 km distant from FLU. Although this study demonstrates the absence of fundamental alterations of genetic structure within the populations of L. gmelinii growing on soils with a high content of fluorides, it is presumed that the reduction of genetic diversity was the genetic response of the FLU population to such an environmental stress as a constantly high concentration of fluorides within the soil.

Differential invertase activity and root growth between Cu-tolerant and non-tolerant populations in Kummerowia stipulacea under Cu stress and nutrient deficiency

There has been no study on key enzymes in sucrose cleavage in metallophyte plants so far, which may be crucial for the plants’ root growth and heavy-metal tolerance maintenance. Here, we tested the hypothesis that the roots of copper tolerant plants should manifest a higher activity of acid invertases that are rate-limiting in sucrose catabolism than non-tolerant plants both for supporting growth and for their maintaining tolerance under Cu stress. Two populations of Kummerowia stipulacea, one from an ancient waste heap at a Cu mine, and the other from a non-contaminated site, were used in the experiments. The plants were grown in 1/2-fold (control) or 1/20-fold (nutrient deficiency) Hoagland’ solution, with (Cu stress) or without (control) 10 μmol/L Cu 2+. Plants from the mine proved to be of Cu tolerance. Cu exposure had a stronger inhibition on root growth and thus resulting in a lower root/shoot ratio in the plants of non-mine population compared to the mine population. Cu exposure showed a stronger inhibition of acid invertase activity of Cu non-tolerant plants than Cu-tolerant plants, while neutral/alkaline invertase was insensitive to Cu. A positive correlation between the activity of acid invertases and the root growth and root/shoot ratio was observed. The results indicated an important role of acid invertases in governing root growth and root/shoot biomass allocation in the plants of mine population. The results also suggested that the higher activities in acid invertases of mine population plants might at least partly associate with the plants’ Cu tolerance, and their higher activities in acid invertases in turn played an role in maintenance of the Cu tolerance by supplying carbon and energy for tolerance mechanisms. In addition, the results showed evidence that neutral/alkaline invertase might play a role in compensating for the depression in sucrose catabolism due to Cu-induced inhibition in acid invertases.

Effects of Copper on Nitrogen Assimilation in Copper-tolerant and Non-tolerant Populations of Elsholtzia haichowensis S.

Two Elsholtzia haichowensis S. populations, copper-tolerant (TLS) and non-tolerant (HA) ones were studied in hydroponic experiment for the nitrogen assimilation and plant growth under excess Cu conditions. The results demonstrated that there were surely the differences in nitrogen assimilation and plant growth between the two populations. Excess Cu caused evident decreases in the shoot and root biomass and root/shoot biomass ratio in HA population while no significant changes happened in TLS population. In addition, in HA population, excess Cu also induced apparent declines in activities of nitrate reductase (NR, EC 1.6.6.1) and glutamine synthetase (GS, EC 6.3.1.2) in the leaves and roots as well as the contents of nitrate, ammonium and amino acids in the roots. In TLS population, excess Cu did not significantly affect the NR activities in the leaves and roots and the nitrate content in the roots, and apparently elevated the root ammonium and amino acids contents, although it also clearly reduced the GS activities in the leaves and roots. Besides, with the addition of Cu in the culture solution, the Cu contents in the leaves and roots of the two populations markedly increased. But this increase was significantly lower in TLS population than that in HA population; the fact might be partly responsible for the relative stabilization of nitrogen assimilation in TLS population compared to that in HA population.

Evolution in closely adjacent plant populations X: long-term persistence of prereproductive isolation at a mine boundary

Flowering time differences between metal-tolerant and nontolerant populations of the grass Anthoxanthum odoratum growing across a mine boundary have persisted for over 40 years. These flowering time differences result in a high degree of prezygotic genetic isolation (isolation index=0.43) between the tolerant mine populations and nontolerant pasture populations. Previous work showing genetic determination of flowering time and a high turnover of individual plants argues strongly for the selective maintenance of this difference.

Arsenic speciation in the earthwormsLumbricus rubellusandDendrodrilus rubidus

Two species of earthworm, Lumbricus rubellus Hoffmeister and Dendrodrilus rubidus (Savigny) collected from an arsenic-contaminated mine spoil site and an uncontaminated site were investigated for total tissue arsenic concentrations and for arsenic compounds by liquid chromatography-mass spectrometry (LC-MS) and liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS). For L. rubellus, whole-body total tissue arsenic concentrations were 7.0 to 17.0 mg arsenic/ kg dry weight in uncontaminated soil and 162 to 566 mg arsenic/kg dry weight in contaminated soil. For D. rubidus, whole-body tissue concentrations were 2.0 to 5.0 mg arsenic/kg dry weight and 97 to 321 mg arsenic/kg dry weight, respectively. Arsenobetaine was the only organic arsenic species detected in both species of earthworms, with the remainder of the extractable arsenic being arsenate and arsenite. There was an increase in the proportion of arsenic present as arsenobetaine in the total arsenic burden. Lumbricus rubellus and D. rubidus have similar life styles, both being surface living and litter feeding. Arsenic speciation was found to be similar in both species for both uncontaminated and contaminated sites, with dose-dependent formation of arsenobetaine. When L. rubellus and D. rabidus from contaminated sites were incubated in arsenic-free soils, the total tissue burden of arsenic diminished. Initially, L. rubellus from the tolerant populations (from the contaminated site) eliminated arsenic in the first 7 d of exposure before accumulating arsenic in tissues, whereas nontolerant populations (from the uncontaminated site) accumulated arsenic linearly. The tolerant and nontolerant L. rubellus eliminated tissue arsenic linearly over 21 d when incubated in uncontaminated soil.

Effects of chromium and nickel on germination and growth in tolerant and non-tolerant populations of Echinochloa colona (L.) Link

The tolerance of populations of a grass, Echinochloa colona, growing abundantly on chromite minewaste dumps, was tested in two separate experiments. Seed-based experiments indicate that the populations growing naturally on uncontaminated sites, germinated better in nutrient solutions without metal than those collected from minewaste dumps. Metal tolerance indices were greater in the plant populations derived from metal contaminated sites and better growth of these plants was noted on mine spoil–soil-mix in the ratio of 1:1; the percentage of seed germination and the rate of seedling growth, however, declined in a soil compost containing 25% mine spoil and 75% uncontaminated (control) soil. Populations of Echinochloa colona occurring naturally on chromite mine spoils, therefore, appear to have developed metal tolerance. It is maintained by a balanced and stable genetic system built up and adjusted by natural selection. Such material is very suitable to be used in restoration work designed to produce an effective vegetation cover to improve the derelict land and to reduce erosion. This finding might be useful in revegetation programmes on metalliferous minewastes.