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No description available.

Lead (Pb) is the number one heavy metal pollutant in the environment. The high cost and environmental concerns of conventional remediation technologies has led to an emerging alternative technology for heavy metal remediation: phytoremediation. This study was set out to advance Pb phytoremediation by investigating plant-associated factors (e.g. polyphenol levels, Pb-tannin chelation, and superoxide dismutase activity) and chemical-based factors (e.g. concentration of Pb, and the type and dosage of chelating agents in treatments) that may affect Pb accumulation. Using a hydroponic system, sand-grown Symphytum officinale L. plants were exposed to nutrient solutions with or without lead nitrate (Pb(NO₃)₂) and ethylenediamine tetraacetic acid (EDTA). Using flame atomic absorption spectroscopy (to measure Pb content) and bovine serum albumin-protein precipitation (to measure polyphenol and tannin levels), a significant in vivo correlation between tannin level and Pb accumulation level was observed in roots of plants exposed to all Pb treatments. Higher tannin containing-lateral roots accumulated significantly more Pb than lowertannin main roots. Transmission electron micrographs of unchelated Pb-treated plants supported these findings, whilst dialysis-based in vitro Pb-chelation studies with crude S. officinale root polyphenol extracts did not. The dialysis method was likely to be subject to fructan interference. A new, more accurate and simple method based on tannin immobilisation was consequently developed. Results using this method supported the hydroponic trends. This new method was also verified with purified tannic acid (from Sigma). Together, these findings demonstrate that S. officinale root tannins have the ability to chelate Pb. This may be a mechanism to cope with Pb stress (adaptive tolerance). Despite the typical signs of Pb stress at root level (e.g. root growth inhibition, and degraded cytoplasms), shoots showed no signs of stress under any Pb treatments. Most importantly, since this chelation-based tolerance mechanism also influences the accumulation levels, the phytochemical composition of plants should also be considered when screening plants for phytoremediation. The level of Pb accumulated in the shoots depended on the concentration of Pb(NO₃)₂ and presence of chelating agents (EDTA or N-[2 acetamido] iminodiacetic acid (ADA)) in the nutrient solution. The highest level of Pb in shoots was between 0.05-0.06% (d.w. on average) using EDTA or ADA, well short of the 1% (d.w.) shoot accumulation target for Pb phytoextraction. The highest level of Pb in the roots (and of all measurements) was with unchelated 500 µM Pb(NO₃)₂; on average 2% (d.w.) accumulated in root. Overall, since S. officinale accumulated Pb predominately in the roots, it is most suited for rhizofiltration and phytostabilisation. Whilst chelating agents enhanced Pb accumulation in shoots, root levels were unexpectedly reduced compared to unchelated Pb treatments. The level of Pb translocated did not completely account for this loss. Minor factors relating to EDTA desorption of roots, EDTA specificity, and charge repulsion of the PbEDTA complex may account for some of the loss, but the main cause remains unclear. In vitro S. officinale cultures were developed and somaclonal variation (involving Pb pre-treatment of petioles) was used as a tool to further investigate, and attempt to improve its Pb phytoremediation potential. The shoots and roots of plants produced from petioles pre-treated with Pb(NO₃)₂ appeared more stressed than those without Pb pre-treatment. After re-treatment with Pb (Pb(NO₃)₂ or PbADA), plants developed from most Pb pre-treated petioles appeared to have reduced Pb accumulation and polyphenol levels, and increased superoxide dismutase activity in roots (although no statistically significant trends were found). Overall, plants produced from Pb pre-treated petioles in this study may have less phytoremediation potential.

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Phytoremediation is a relatively new technology that uses plants for the clean up of contaminated soils.Its low cost, simplicity and environmentally friendly approach make this technology a viable option for remediation but the main drawback is that it must be considered as long term alternative given its slow speed. This work is the first to report the use of Plant Growth Regulators(PGR)to enhance the performance of phytoremediation so that less time is needed for remediation.Soil samples were taken from a heavy metal contaminated, abandoned mine site for plant growth trials. A clean soil was also analysed and used for reference.Trials were carried out by growing corn in the contaminated soils and using various concentrations of IBA and NAA together with soil amedments to see if these could increase the accumulation of Zn, Mn, Cu, Bb and Fe in corn. Several further tests were conducted and results noted. / Doctor of Philosophy (PhD)

For the successful development of a hyperaccumulating plant sufficient for use in phytoremediation strategies, a thorough understanding of the mechanism of hyperaccumulation is required. A proteomic survey of the response of plants to metal exposure is a step towards this understanding. The frd3-3 metal accumulating mutant of Arabidopsis thaliana and its non-accumulating wildtype parental ecotype, Columbia, were grown hydroponically in growth chamber experiments and exposed to copper in the growth medium. The responses of the global and copper-targeted proteomes were examined both spatially and temporally. Exposure to copper caused a general increase in protein abundance, however, a prolonged exposure to copper that approached toxicity caused a decrease in protein abundance. The protein species differed between the roots of the two genotypes, with more defense- and stress-related proteins, and fewer transport and storage proteins identified in the mutant when compared to the wildtype. Proteomic evidence suggests that in the mutant the uptake and transport of copper ions to the aerial tissues is regulated. The protein expression patterns over time demonstrate a constitutive expression of defense- and stress-related proteins in the mutant, whereas the wildtype expression was one of induction. The constitutive expression of key defense proteins suggests a state-of-readiness for metal exposure in the mutant. The plant response to reactive oxygen species, as a consequence of copper exposure, is important in the overall metal accumulation mechanism. A suppression of the oxidative burst produced upon exposure to heavy metals is suggested by the proteomic evidence.

Quantifying the effects of hydrocarbon contamination on hybrid poplar fine root dynamics provides information about how well these trees tolerate the adverse conditions imposed by the presence of petroleum in the soil. Infection by ectomycorrhizal (ECM) fungi may benefit hybrid poplar growing in contaminated soils by providing greater access to water and nutrients and possibly inducing greater contaminant degradation. The overall objectives of this research were to: 1) investigate the relationship between the varying concentrations of total petroleum hydrocarbons (TPH) and nutrients across a hydrocarbon-contaminated site, as well as interactions between these contaminants and physical and chemical soil properties; 2) quantify the effects of these properties on the spatial and temporal patterns of fine root production for Griffin hybrid poplar (<i>P. deltoids </i> x <i>P. petrowskyana</i> c.v. Griffin); and (3) quantify the effect of ectomycorrhizal colonization on hybrid poplar fine root dynamics and N and P uptake when grown in diesel contaminated soil under controlled conditions. A minirhizotron camera provides a nondestructive approach for viewing roots in situ. This camera was used in both the field and growth chamber experiments to provide the data necessary for estimating fine root production. The field study was conducted at Hendon, SK, Canada. Twelve minirhizotron tubes were distributed across the field site and facilitated quantification of fine root production in areas of varying contamination levels. Residual hydrocarbon contamination was positively correlated with soil total C and N, which may suggest that the hydrocarbons remaining in the soil are associated with organic forms of these nutrients or increased microbial biomass. Total fine root production at the site was greater in the 0- to 20-cm depth (1.27 Mg/ha) than the 20- to 40-cm depth (0.51 Mg/ha) in 2004. Fine root production was stimulated by small amounts of hydrocarbon contamination at the field site. Nonlinear regression described fine root production as increasing linearly up to approximately 500 mg/kg TPH, then remaining constant as contamination increased. This trend was most pronounced in the 0- to 20-cm soil layer, with a (r&178; = 0.915). Stimulation of fine root production in the presence of hydrocarbons has significant implications for phytoremediation. If hybrid poplar can maintain increased root production in hydrocarbon contaminated soils, the rhizosphere effect will be exaggerated and increased degradation of contaminants is likely to occur. Under controlled conditions, colonization of hybrid poplar roots by the ectomycorrhizal fungus <i>Pisolithus tinctorius</i>increased fine root production in a diesel contaminated soil (5000 mg diesel fuel/kg soil) compared to non-colonized trees growing in the same soil. Fine root production was 56.6 g/m&178; in the colonized treatment and 22.6 g/m&178; in the non-colonized treatment. In diesel contaminated/ECM colonized treatment, hybrid poplar leaf N and P concentrations after 12 wk were 23.1 and 3.6 g/kg, respectively. In diesel contaminated/non-colonized treatment, N and P concentrations were 15.7 and 2.7 g/kg, respectively. After 12 wk, 5.0&37; of the initial concentration of diesel fuel remained in the soil of the non-colonized treatment and 6.7&37; remained in the colonized treatment. Both treatments removed more contaminants from the soil than an unplanted control, which contained 8.9&37; of the initial diesel fuel concentration after 12 wk. Significantly more hydrocarbons were found sequestered in hybrid poplar roots from the colonized treatment (354.1 mg/kg) than in the non-colonized treatment (102.2 mg/kg). The results of this study indicate that hybrid poplar may be good candidates for use in phytoremediation of petroleum hydrocarbons because of the stimulation of fine root production at low levels of hydrocarbon contamination. However, colonization of hybrid poplar growing in diesel contaminated soil by <i>P. tinctorius</i> inhibited remediation of diesel fuel.

Quantifying the effects of hydrocarbon contamination on hybrid poplar fine root dynamics provides information about how well these trees tolerate the adverse conditions imposed by the presence of petroleum in the soil. Infection by ectomycorrhizal (ECM) fungi may benefit hybrid poplar growing in contaminated soils by providing greater access to water and nutrients and possibly inducing greater contaminant degradation. The overall objectives of this research were to: 1) investigate the relationship between the varying concentrations of total petroleum hydrocarbons (TPH) and nutrients across a hydrocarbon-contaminated site, as well as interactions between these contaminants and physical and chemical soil properties; 2) quantify the effects of these properties on the spatial and temporal patterns of fine root production for Griffin hybrid poplar (<i>P. deltoids </i> x <i>P. petrowskyana</i> c.v. Griffin); and (3) quantify the effect of ectomycorrhizal colonization on hybrid poplar fine root dynamics and N and P uptake when grown in diesel contaminated soil under controlled conditions. A minirhizotron camera provides a nondestructive approach for viewing roots in situ. This camera was used in both the field and growth chamber experiments to provide the data necessary for estimating fine root production. The field study was conducted at Hendon, SK, Canada. Twelve minirhizotron tubes were distributed across the field site and facilitated quantification of fine root production in areas of varying contamination levels. Residual hydrocarbon contamination was positively correlated with soil total C and N, which may suggest that the hydrocarbons remaining in the soil are associated with organic forms of these nutrients or increased microbial biomass. Total fine root production at the site was greater in the 0- to 20-cm depth (1.27 Mg/ha) than the 20- to 40-cm depth (0.51 Mg/ha) in 2004. Fine root production was stimulated by small amounts of hydrocarbon contamination at the field site. Nonlinear regression described fine root production as increasing linearly up to approximately 500 mg/kg TPH, then remaining constant as contamination increased. This trend was most pronounced in the 0- to 20-cm soil layer, with a (r&178; = 0.915). Stimulation of fine root production in the presence of hydrocarbons has significant implications for phytoremediation. If hybrid poplar can maintain increased root production in hydrocarbon contaminated soils, the rhizosphere effect will be exaggerated and increased degradation of contaminants is likely to occur. Under controlled conditions, colonization of hybrid poplar roots by the ectomycorrhizal fungus <i>Pisolithus tinctorius</i>increased fine root production in a diesel contaminated soil (5000 mg diesel fuel/kg soil) compared to non-colonized trees growing in the same soil. Fine root production was 56.6 g/m&178; in the colonized treatment and 22.6 g/m&178; in the non-colonized treatment. In diesel contaminated/ECM colonized treatment, hybrid poplar leaf N and P concentrations after 12 wk were 23.1 and 3.6 g/kg, respectively. In diesel contaminated/non-colonized treatment, N and P concentrations were 15.7 and 2.7 g/kg, respectively. After 12 wk, 5.0&37; of the initial concentration of diesel fuel remained in the soil of the non-colonized treatment and 6.7&37; remained in the colonized treatment. Both treatments removed more contaminants from the soil than an unplanted control, which contained 8.9&37; of the initial diesel fuel concentration after 12 wk. Significantly more hydrocarbons were found sequestered in hybrid poplar roots from the colonized treatment (354.1 mg/kg) than in the non-colonized treatment (102.2 mg/kg). The results of this study indicate that hybrid poplar may be good candidates for use in phytoremediation of petroleum hydrocarbons because of the stimulation of fine root production at low levels of hydrocarbon contamination. However, colonization of hybrid poplar growing in diesel contaminated soil by <i>P. tinctorius</i> inhibited remediation of diesel fuel.

For the successful development of a hyperaccumulating plant sufficient for use in phytoremediation strategies, a thorough understanding of the mechanism of hyperaccumulation is required. A proteomic survey of the response of plants to metal exposure is a step towards this understanding. The frd3-3 metal accumulating mutant of Arabidopsis thaliana and its non-accumulating wildtype parental ecotype, Columbia, were grown hydroponically in growth chamber experiments and exposed to copper in the growth medium. The responses of the global and copper-targeted proteomes were examined both spatially and temporally. Exposure to copper caused a general increase in protein abundance, however, a prolonged exposure to copper that approached toxicity caused a decrease in protein abundance. The protein species differed between the roots of the two genotypes, with more defense- and stress-related proteins, and fewer transport and storage proteins identified in the mutant when compared to the wildtype. Proteomic evidence suggests that in the mutant the uptake and transport of copper ions to the aerial tissues is regulated. The protein expression patterns over time demonstrate a constitutive expression of defense- and stress-related proteins in the mutant, whereas the wildtype expression was one of induction. The constitutive expression of key defense proteins suggests a state-of-readiness for metal exposure in the mutant. The plant response to reactive oxygen species, as a consequence of copper exposure, is important in the overall metal accumulation mechanism. A suppression of the oxidative burst produced upon exposure to heavy metals is suggested by the proteomic evidence.

No description available.