PhD Exit Seminar – Devrim Coskun (Kronzucker lab)

PhD Exit Seminar

Thursday August 25^th, 11:10 am – Room SW 403, University of Toronto at Scarborough

Devrim Coskun (Kronzucker lab)

“On the Roles of Membrane Channels in Plant Mineral Nutrition and Toxicity“

Abstract

The study of plant mineral nutrition and toxicity has made major strides recently, particularly at the level of molecular genetics. Arguably, however, this has been at the expense of “classical” physiology, which is of concern because critical physiological examinations of cellular and molecular models in planta are needed if extrapolations of these models to “real-world” (field-level) conditions are to be made. This is particularly urgent in the face of increasing environmental degradation and global food demands. To this end, the preset work explores the physiological role of membrane channels in higher-plant nutrition and toxicology, building upon foundational work in nutritional physiology and applying the important new discoveries in the areas of molecular-genetics and electrophysiology. Combining radioisotopic (⁴²K⁺ and ¹³NH₃/¹³NH₄⁺) flux kinetics and compartmentation analyses with techniques in electrophysiology, mutant analysis, gas exchange, fluorescence imaging and tracing, and tissue mineral-content analysis, this work investigates the involvement of inward- and outward-rectifying Shaker-like K⁺ channels (KIR and KOR, respectively), nonselective cation channels (NSCCs), and aquaporins (AQPs), in K⁺ and NH₃/NH₄⁺ transport under conditions of both stress (low K⁺, salinity, and ammonium toxicity) and non-stress, in the intact plant. Efflux analyses showed that KOR channels mediate K⁺ efflux in barley roots only at low external [K⁺] (<1 mM), above which transmembrane efflux ceased altogether, and demonstrated their lack of involvement in Na⁺-induced K⁺ efflux in rice roots, an important salinity-stress response. Influx analyses elucidated the involvement of KIR channels in high- and low-affinity K⁺ uptake in barley and Arabidopsis roots, demonstrating dramatic capacity and plasticity, as well as their relevance to salinity stress. By contrast, no evidence of NSCC activity was found under similar conditions. Lastly, rapid transmembrane cycling of NH₃, likely mediated by AQPs, was demonstrated to underlie ammonium toxicity in barley roots, fundamentally revising the mechanistic model of low-affinity NH₃/NH₄⁺ transport.