MSc Exit Seminar – Gregory Martyn (Vanlerberghe lab)

MSc Exit Seminar

Thursday February 4^th, 10:10 am – Room SW403, University of Toronto at Scarborough

Gregory Martyn (Vanlerberghe lab)

“The Impact of Alternative Oxidase on Nitrogen Stress in Nicotiana tabacum“

Abstract

Nitrogen applied in limiting quantities (low nitrate) or as an unfavourable source (ammonium) disrupts the fine-tuned rates of turnover of the adenylate and pyridine nucleotide pools in plants leading to stress. The alternative oxidase (AOX) is an abiotic stress response protein that relaxes the tight coupling between NAD(P)H oxidation and ATP synthesis, thus restoring cellular energy homeostasis. To investigate whether AOX has an impact on these “nitrogen stress” scenarios, wild-type Nicotiana tabacum were compared to AOX knockdown and overexpression lines grown in either nitrate or ammonium at 100µm, 1mM, 5mM concentrations as well as under 16 day nitrogen deprivation and 10mM ammonium. Using gas exchange and chlorophyll a fluorescence in addition to qRT-PCR and western blotting we demonstrate that AOX was imposing photosystem stoichiometry adjustments in plants grown at 100 µM nitrate. Under severe nitrogen deprivation, mitochondrial respiration in the dark (R_D) and light (R_L) were consistent with improved photosynthetic capacity and AOX overexpression. All plants grown under 10mM ammonium displayed symptoms of ammonium toxicity. AOX expression under ammonium toxicity was significantly positively correlated with photosynthetic capacity in later parts of the day. These results demonstrate that AOX is an important component of the nitrogen stress response in plants and could even be beneficial under extreme nitrogen stress conditions.