9:00 am - 10:00 am
Event details: A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES MSc Final Exam Seminar by Nicolas Perrault. This seminar is open to the general public to attend.
MSc with Drs. Uwe Hacke and Joan Laur.
Thesis Topic: Water and arsenic movement in Salix nigra under simulated phytoremediation conditions
Due to both natural sources and anthropogenic activities, arsenic is a major contaminant, to which millions of people are exposed worldwide. While costly and ecologically unsound decontamination techniques exist, willow plantations can be particularly well suited to phytoremediate soils containing hazardous levels of arsenic. For this purpose, their ecophysiological properties need to be properly understood. From a phytoextraction perspective, plant-water relations explain the mobilization of hydrophilic contaminants from bulk soil towards the plant body. Within plants, the movement of both water and arsenic is finely regulated by the local modulation of the expression of genes encoding membrane transport proteins. This study aims to elucidate the simultaneous mechanisms of arsenic and water transport in black willow trees (Salix nigra) used in a phytoremediation context. Emphasis is placed on understanding the hydraulic redistribution phenomenon that could explain the complex change of soil contamination profiles observed in the field. To this end, greenhouse experiments were set up in an ingenious dual-compartment system in order to mimic an arsenic contamination of the deep soil profiles and drought of the more superficial layers. Soil water content, arsenic concentration, plant growth and root mRNA profiles were carefully monitored. The results presented here show that although the root systems of S. nigra makes significant hydraulic redistribution, this passive phenomenon alone does not explain the movement of arsenic from contaminated soil layers to healthy soil patches. On the contrary, RNA profiling results highlight the gene expression response to both arsenic and drought. Stress responsive genes, as well as the regulation of aquaporins, phosphate transporters and ABC transporters, provide insights on the mechanisms underlying the fate of arsenic in the ecosystem. This transport mechanism appears to be actively restrained at the plant transcriptomic level and depends on the unavoidable degradation of arsenic-accumulating root tissue.