PhD Proposal Exam – Ahmed Hamam (Kronzucker lab)

PhD Proposal Exam

Thursday March 10, 12:10 pm – Room MW 229, University of Toronto at Scarborough

Ahmed Hamam (Kronzucker lab)

“A Critical Re-examination of Sodium Transport and Its Role in Salinity Stress in Plants“

Abstract

Soil salinity is a major threat to agriculture, affecting more than 6% of the world’s total land area. NaCl is the most soluble and widespread salt on earth, and at high cytosolic concentrations, is considered metabolically toxic. For decades, researchers have been investigating the pathways of Na⁺ transport and its distribution in plants, especially at the point of contact, the root surface, but the underlying mechanisms and pathways remain poorly resolved. According to the current proposed model, Na⁺ enters the roots passively down its electrochemical gradient at very high rates, and then actively pumped out of the cytosol at nearly the same rate. This model of rapid Na⁺ cycling has been called into question, as the energy requirement to mediate such high fluxes is unfeasible, and evidence from electrophysiological and radiotracer measurements are conflicting. The aim of this project is to critically re-examine the credibility of this model, by systematically comparing radiotracer and electrophysiological recordings in the model systems barley (Hordeum vulgare), rice (Oryza sativa), and Arabidopsis thaliana. Based on my progress to date, it would appear that most of the reported Na⁺ fluxes are a gross overestimation of symplastic flow, and more likely to be predominately apoplastic in nature.