·¬ÇÑÉçÇø

Topic

Proanthocyanidins in Poplar Roots: Effects on Mycorrhizal Colonization and Nitrogen Uptake

Department of Biology

Date & location

• Thursday, October 10, 2024
• 9:00 A.M.
• Clearihue Building, Room B017

Examining Committee

Supervisory Committee

• Dr. Barbara Hawkins, Department of Biology, ·¬ÇÑÉçÇø (Co-Supervisor)
• Dr. Peter Constabel, Department of Biology, UVic (Co-Supervisor)
• Dr. Paul De la Bastide, Department of Biology, UVic (Member)

External Examiner

• Dr. Melanie Jones, Department of Biology, University of British Columbia Okanagan

Chair of Oral Examination

• Dr. Jeremy Wulff, Department of Chemistry, UVic

Abstract

Proanthocyanidins (PAs), also known as condensed tannins, are widespread plant secondary metabolites, especially common in trees. PAs are known for their roles in plant defense and soil nutrient cycling, and their many applications in human medicine and diet. Although substantial research has focused on PA function in plant shoots, few studies have investigated their roles in roots. Some research indicates that PAs act as anti-fungal compounds, suggesting PAs in roots could negatively affect beneficial fungi in soils such as mycorrhizal fungi, which provide nutrients, including nitrogen (N), to host plants. Notably, the growth of the ectomycorrhizal (EcM) fungus Laccaria bicolor was inhibited in vitro by a purified extract of poplar PAs. Therefore, I aimed to evaluate the effects of PAs in roots on mycorrhizal colonization as well as on N uptake by colonized roots.

Poplar (Populus. tremula x P. tremuloides) was chosen as the study species because poplars produce a wide range of phenolic compounds, including PAs. I utilized transgenic lines developed previously that have high and low PA concentrations in plant tissues, including roots. Plants from each line were equally divided into two treatment groups inoculated with either the EcM fungus L. bicolor or the arbuscular mycorrhizal (AM) fungus Rhizophagus irregularis, and one non-inoculated control group. Plants were grown in a sandwich culture system that allows co-culture of the mycorrhizal fungi and roots, or inoculated with the fungi in soil in a greenhouse experiment. Uptake of ammonium (NH₄⁺) and nitrate (NO₃⁻) by plant roots was measured using a microelectrode ion flux measurement system (MIFE^TM), and by ¹⁵N-labelling.

Contrary to my prediction, the poplar line with low-PAs/phenolics in roots was less colonized by EcM in both sandwich and soil culture. Additionally, plants from all lines inoculated with EcM in sandwich culture system had lower root PA concentrations. Although no significant difference in N uptake among plant lines or mycorrhizal treatments was observed, NH₄⁺ uptake was greater than NO₃⁻ uptake. Understanding the effects of the interaction of root PAs and mycorrhizal fungi on mycorrhizal colonization and N uptake will contribute to our knowledge of the ecological and physiological impacts of PAs in the rhizosphere