Water and arsenic movement in Salix nigra under simulated phytoremediation conditions

• Author / Creator

  Perrault, Nicolas

• Arsenic is a highly toxic and ubiquitous element. To this day, millions of people are exposed to arsenic contamination, which poses global health concerns. Phytoextraction performed with willows, a form of phytoremediation, is a promising means of cleaning up soils containing hazardous levels of arsenic. Plant-water relations and cell transport activity both play key roles in this decontamination process, as they explain the movement of
  hydrophilic contaminants from bulk soil into the plant. Both water and arsenic uptake, and their movement across cell membranes, are regulated by transport proteins. This thesis
  studies the processes of arsenic and water transport in willows used in a phytoremediation context. Through two greenhouse experiments using a double-compartment design, physiological activity monitoring and mRNA profiling, we investigated the movement of water and arsenic in the soil and within willows under experimental treatments of drought and soil contamination. Our results show that a process of water redistribution towards dry surface soil occurs through Salix nigra root system, although aquaporins activity is repressed in surface roots exposed to drought. Based on mRNA profiles, we highlight the intricate willows’ root activity in response to both arsenic and drought at the gene expression level. The expression of aquaporins, phosphate transporters and ABC
  transporters in roots identifies key genes responsible for water and arsenic transport under stress conditions. Their expression level indicates the presence of a weak exclusion
  mechanism of arsenic in Salix nigra, allowing the easy uptake of the contaminant from deep soil. Simultaneously, the repression of aquaporin genes in surface roots blocks a
  possible efflux pathway, confining the arsenic inside the plant. Most importantly, adverse growth conditions caused by contamination exposure and an extended episode of drought
  in surface soil are more likely responsible for root decay, and induce the arsenic redistribution to surface soil layers. This process does not seem to result from the hydraulic redistribution observed in the short-term. This process should be considered in the planning of phytoremediation experiments in the field, either by trying to prevent it with proper irrigation, or by exploiting it in rotational cultures allowing the decontamination of deep and shallow soil in succession. The activity of transporter genes identified from the mRNA profiling results needs to be investigated with further testing to uncover their specific roles in arsenic transport, for example with heterologous expression systems. This knowledge could allow for the development of more efficient plants for decontamination purposes, through genetic engineering or genotypic selection of plants favoring contaminant transport.

• Subjects / Keywords

  • Arsenic
  • Phytoremediation
  • Hydraulic redistribution
  • Willow
  • Aquaporin
  • Water

• Graduation date

  Fall 2023

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-5y9z-0m36

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.