The accumulation of metals, PAHs and alkyl PAHs in the roots of Echinacea purpurea.

We examined the accumulation of polycyclic aromatic hydrocarbons (PAHs), alkyl PAHs, and toxic metals in soils by the roots of Echinacea purpurea (L.) Moench, in a 20-week greenhouse study and a 2-year field study. In the greenhouse study, inoculation by arbuscular mycorrhizal fungus (AMF), Rhizoglomus intraradices (N.C. Schenck & G.S. Sm.). increased the first order accumulation rates (k1) for PAHs by 10-fold, though had no effect on the bioaccumulation rates of toxic metals. In the greenhouse study, PAHs concentrations in soil increased over time with AMF inoculation, suggesting AMF promote 'solvent depletion' in soils by enhancing absorption of minerals and carbon by roots, concentrating the more hydrophobic PAHs in the residual soil. Under field conditions, contaminant concentrations in soils remained unchanged over the 2-year duration of the study. Despite this, all contaminants in E. purpurea roots increased significantly, as a result of a long term extraction of contaminants by plants from soil and a reduction in soil volume as a result of plant growth. First order accumulation rates by roots were inversely correlated to log Kow for the PAHs and alkyl PAHs, indicating that accumulation is inversely related to the compound's hydrophobicity. This study is the first to our knowledge to assess the accumulation of alkyl PAHs by roots, with implications for soil bioremediation by plants because alkyl PAHs are a major source of petrogenic contamination in soils.

Preventable obstetrical interventions: how many caesarean sections can be prevented in Canada?

Public health authorities have been alarmed by the progressive rise in rates of Caesarean section in Canada, approaching one birth in three in several provinces. We aimed therefore to consider what were preventable obstetrical interventions in women with a low-risk pregnancy and to propose an analytic framework for the reduction of the rate of CS. We obtained statistical variations of CS rates over time, across regions, and within professional practices from MED-ÉCHO, the Quebec hospitalization database, from 1969 to 2009. Data were extracted from a recent systematic review of the cascade of obstetrical interventions to calculate the population-attributable fractions for each intervention associated with an increased probability of CS. We thereby identified expectant management (as an alternative to labour induction) and planned vaginal birth after CS as the leading strategies for potentially reducing rates of CS in women at low risk. For vaginal birth after CS, an increase to its 1995 level could lower the current CS rate of 23.2% (2009 to 2010) to 21.0%. Other alternatives to obstetrical interventions with a potential for lowering CS rates included non-pharmacological pain control methods (such as continuous support during childbirth) in addition to usual care, intermittent auscultation of the fetal heart (instead of electronic fetal monitoring), and multidisciplinary internal quality assessment audits. We believe, therefore, that the concept of preventable CS is supported by empirical evidence, and we identified realistic strategies to maintain a CS rate in Quebec near 20%.

Les autorités en matière de santé publique ont été alarmées par la hausse graduelle des taux de césarienne (CS) au Canada (près d'une naissance sur trois dans plusieurs provinces). Nous avons donc cherché à identifier les interventions obstétricales qui pouvaient être évitées chez les femmes qui connaissent une grossesse les exposant à de faibles risques, ainsi qu'à proposer un cadre analytique pour la réduction du taux de CS. Les variations statistiques, entre 1969 et 2009, des taux de CS avec le temps, d'une région à l'autre et en fonction des pratiques professionnelles ont été tirées de MED-ÉCHO (la base de données sur l'hospitalisation au Québec). Des données ont été tirées d'une récente analyse systématique de la cascade d'interventions obstétricales en vue de calculer les fractions étiologiques du risque pour chacune des interventions associées à une probabilité accrue de CS. Nous avons ainsi identifié la prise en charge non interventionniste (à titre de solution de rechange au déclenchement du travail) et l'accouchement vaginal planifié après CS comme étant les principales stratégies pouvant permettre la réduction des taux de CS chez les femmes exposées à de faibles risques. Pour ce qui est de l'accouchement vaginal après CS, une hausse jusqu'à son niveau de 1995 pourrait faire passer le taux actuel de CS de 23,2 % (de 2009 à 2010) à 21,0 %. Parmi les solutions de rechange aux interventions obstétricales qui présentent le potentiel d'abaisser les taux de CS, on trouvait les méthodes non pharmacologiques de maîtrise de la douleur (comme l'offre d'un soutien continu pendant l'accouchement) s'ajoutant aux soins habituels, l'auscultation intermittente du cœur fœtal (plutôt que le monitorage électronique du fœtus) et les audits internes multidisciplinaires de la qualité. Nous estimons donc que le concept de la CS évitable est soutenu par des données empiriques et nous avons identifié des stratégies réalistes permettant d'assurer le maintien, au Québec, d'un taux de CS se situant près de 20 %.

Some like it toxic.

Humans are notorious for disturbing terrestrial ecosystems worldwide, especially those that are in close proximity to urban areas. This disturbance has involved the accumulation of various types of chemical pollutants, of either agricultural or industrial origins, in both soil and water ecosystems. Pollutants have sometimes included essential plant nutrients, such as phosphate and nitrate, which have piled up throughout the years in many ecosystems as a consequence of aggressive agricultural practices, and a number of toxic or trace metals, e.g. iron, nickel or zinc that are important at low levels for the fitness of living organisms, but otherwise toxic at high concentrations (Ker & Charest 2010; Audet & Charest 2008). In order to reduce the load of toxic elements, scientists have used the natural capacity of several plant species to sequestrate them from the soil and, ultimately, render them harmless. This process, called phytoremediation, is rather slow, as most plants take years to build up their biomass but has been shown to be 'boostable' under experimental conditions in the presence of a particular group of plant symbionts in the soil ­ the arbuscular mycorrhizal fungi (AMF) (Gohre & Paszkowski 2006). These latter organisms are now widely recognized as being very beneficial for purposes of phytoremediation, but their biodiversity in the most disturbed ecosystems is still virtually unknown. Are these fungi really abundant in heavily polluted soils, or are their communities shrunken down like those of other microorganisms in the presence of heavy pollution? In this issue of Molecular Ecology, the study by Hassan et al. (2011) provides answers to these specific questions by determining the extent of AMF biodiversity across several urbanized areas in the City of Montre´al.

Nickel remediation by AM-colonized sunflower.

This greenhouse study aimed to examine the contribution of arbuscular mycorrhizal (AM) colonization on the uptake of and tolerance to nickel (Ni) in sunflower (Helianthus annuus L.). We hypothesized that AM colonization increases Ni content and tolerance in sunflower grown under varying soil Ni concentrations. The combined effect of AM colonization and soil Ni input on the assimilation of nitrogen, in particular the activity of glutamine synthetase (GS), in sunflower plants was also investigated. A factorial experimental design was performed with sunflower cv. Lemon Queen, with or without the AM fungus, Glomus intraradices Schenck & Smith, and treated with 0, 100, 200, or 400 mg Ni kg(-1) dry soil (DS). The AM colonization significantly enhanced plant growth and Ni content, especially at the lower soil Ni treatments. Furthermore, the AM plants exposed to the highest soil Ni level of 400 mg Ni kg(-1) DS had a significantly higher shoot Ni extracted percentage than non-AM plants, suggesting that the AM symbiosis contributed to Ni uptake, then its translocation from roots to shoots. The AM colonization also significantly increased the GS activity in roots, this being likely an indicator of an enhanced Ni tolerance. These findings support the hypothesis that AM symbiosis contributes to an enhanced Ni plant uptake and tolerance and should be considered as part of phytoremediation strategies.

Root colonization by an arbuscular mycorrhizal (AM) fungus increases growth and secondary metabolism of purple coneflower, Echinacea purpurea (L.) Moench.

Purple coneflower, Echinacea purpurea (L.) Moench, is an important phytomedicinal species that contains phenolics and alkamides with antipathogenic properties. This study aimed to examine the effect of arbuscular mycorrhizal (AM) colonization on the physiology and biochemistry of E. purpurea. It was hypothesized that AM colonization enhances the growth and secondary metabolism in E. purpurea. In this regard, a 13-week factorial greenhouse experiment was performed with E. purpurea, inoculated (or not) with the AM fungus Glomus intraradices Schenck & Smith. Overall, the results indicated that AM colonization significantly increased the mass of shoots and roots and the concentrations of proteins and most of the phenolics in the roots. Hence, the selected trait of mycorrhiza could play an important role in optimizing the growth of E. purpurea by inducing the production of secondary phytomedicinal metabolites.

Allocation plasticity and plant-metal partitioning: meta-analytical perspectives in phytoremediation.

In this meta-analysis of plant growth and metal uptake parameters, we selected 19 studies of heavy metal (HM) phytoremediation to evaluate trends of allocation plasticity and plant-metal partitioning in roots relative to shoots. We calculated indexes of biomass allocation and metal distribution for numerous metals and plant species among four families of interest for phytoremediation purposes (e.g. Brassicaceae, Fabaceae, Poaceae, and Solanaceae). We determined that plants shift their biomass and distribute metals more to roots than shoots possibly to circumvent the challenges of increasing soil-HM conditions. Although this shift is viewed as a stress-avoidance strategy complementing intrinsic stress-tolerance, our findings indicate that plants express different levels of allocation plasticity and metal partitioning depending on their overall growth strategy and status as 'fast-grower' or 'slow-grower' species. Accordingly, we propose a conceptual model of allocation plasticity and plant-metal partitioning comparing 'fast-grower' and 'slow-grower' strategies and outlining applications for remediation practices.

Heavy metal phytoremediation from a meta-analytical perspective.

We conducted a literature survey and correlated heavy metal (HM) uptake and plant growth factors from published data to estimate the effectiveness of phytoextraction. The indicators of the actual plant HM uptake showed positive correlations with soil-HM concentrations, while the relative plant HM uptake showed negative correlations. Plant growth was negatively correlated with both the plant and soil-HM concentrations. These significant relationships were found for the majority of HM tested (e.g. Zn, Cd, Pb, Cu, Cr, and Fe) with a few exceptions (e.g. Ni, Co, and Mn). After fitting the correlation coefficients, the highest proportion of variance among the studies was mainly due to the experimental parameters or the plant species. When the metabolic costs of HM uptake are taken into account, the phytoextraction appears to be less effective beyond critical HM concentrations. Despite these constraints, it is emphasized that HM phytoextraction can play an important role in bioremediation.

Dynamics of arbuscular mycorrhizal symbiosis in heavy metal phytoremediation: meta-analytical and conceptual perspectives.

To estimate dynamics of arbuscular mycorrhizal (AM) symbiosis in heavy metal (HM) phytoremediation, we conducted a literature survey and correlated HM uptake and relative plant growth parameters from published data. After estimating AM feedback responses for these parameters at low and high soil-HM concentration intervals, we determined that the roles of AM symbiosis are characterized by (1) an increased HM phytoextraction via mycorrhizospheric 'Enhanced Uptake' at low soil-HM concentrations, and (2) a reduced HM bioavailability via AM fungal 'Metal-Binding' processes at high soil-HM levels, hence resulting in increased plant biomass and enhanced plant tolerance through HM stress-avoidance. We present two conceptual models which illustrate the important compromise between plant growth, plant HM uptake and HM tolerance, and further emphasize the importance of AM symbiosis in buffering the soil environment for plants under such stress conditions.

Effects of AM colonization on "wild tobacco" plants grown in zinc-contaminated soil.

This greenhouse study aimed to determine the effect of colonization by the arbuscular mycorrhizal (AM) fungus (Glomus intraradices Schenck & Smith) on the "wild" tobacco (Nicotiana rustica L. var. Azteca), under soil-zinc (Zn) conditions. Plants of N. rustica were grown in AM or non-AM inoculated substrate and subjected to four soil-[Zn] concentrations (0, 50, 100, and 250 mg Zn kg(-1) dry soil). The AM root colonization increased markedly from 14 to 81% with the increasing soil-[Zn] and the mycorrhizal structures were significantly more abundant at the highest soil-[Zn], suggesting that Zn may be involved directly or indirectly in AM root colonization. In addition, total Zn content or Zn concentrations in shoots and roots were shown to increase as soil-[Zn] increased in both AM and non-AM plants. As for the growth parameters studied, there were no significant differences between treatments despite the increase in Zn content or concentration. The AM roots subjected to the highest soil-[Zn] had a significant reduction by about 50% of total Zn content and Zn concentration compared to non-AM roots. Still, the relative extracted Zn percentage decreased dramatically as soil-[Zn] increased. Soil pH was significantly lower in non-AM than AM treatments at the highest soil-[Zn]. In summary, AM plants (particularly roots) showed lower Zn content and concentration than non-AM plants. In this regard, the AM fungi have a protective role for the host plant, thus playing an important role in soil-contaminant immobilization processes; and, therefore, are of value in phytoremediation, especially when heavy metals approach toxic levels in the soil.

Nitrogen transfer and assimilation between the arbuscular mycorrhizal fungus Glomus intraradices Schenck & Smith and Ri T-DNA roots of Daucus carota L. in an in vitro compartmented system.

Nitrogen metabolism was examined in monoxenic cultures of carrot roots (Daucus carota L.) colonized with the arbuscular mycorrhizal (AM) fungus Glomus intraradices Schenck & Smith. Glutamine synthetase and glutamate dehydrogenase activities were significantly increased in mycorrhizal roots for which only the extraradical mycelium had exclusive access to NH4NO3 in a distinct hyphal compartment inaccessible to the roots. This was in comparison with the water controls but was similar to the enzyme activities of non-arbuscular-mycorrhizal (non-AM) roots that had direct access to NH4NO3. In addition, glutamate dehydrogenase activity was significantly enhanced in AM roots compared with non-AM roots. Carrot roots took up 15NH4+ more efficiently than 15NO3-, and the extraradical hyphae transfered 15NH4+ to host roots from the hyphal compartment but did not transfer 15NO3-. The extraradical mycelium was shown, for the first time, to have a different glutamine synthetase monomer than roots. Our overall results highlight the active role of AM fungi in nitrogen uptake, transfer, and assimilation in their symbiotic root association.

Maternally-induced modification of progeny phenotypes in the C4 weed Echinochloa crus-galli: An analysis of seed constituents and performance.

To clarify the physiological basis of maternal inheritance we examined the effect of the thermal environment of mother plants of Echinochloa crus-galli on subsequent seed mass, content and quality. The same plants were grown in a warm and a cold environment until seeds were produced and, since E. crus-galli is a highly inbred species, the observed variation in seed production was a purely plastic response to the environment. When mother plants were grown at high temperature, average seed mass, variance and germinability were low. Cold maturation led to the production of more large seeds than warm maturing temperature. The latter seeds were deprived of reserve constituents. Seeds matured at high temperature had high concentrations of K+ and Mn2+ but lower concentrations of starch and protein.