Abstract Detail

Biotic and abiotic stress

Martyn, Greg [1], Hayes, Fallon [2], Vanlerberghe, Greg [3].

Evaluating the role of mitochondrial alternative oxidase during nitrogen assimilation.

Effective carbon and energy metabolism requires fine-tuned rates of turnover of the adenylate and pyridine nucleotide pools to maintain cellular energy homeostasis. One means to preserve energy homeostasis is through modulating the activity of a mitochondrial electron transport chain component termed alternative oxidase (AOX). AOX provides a means to relax the otherwise tight coupling between NAD(P)H oxidation and ATP synthesis. For example, we have shown that AOX is essential to optimizing photosynthesis during drought, when energy homeostasis in the chloroplast is perturbed by the reduced Calvin cycle activity resulting from limited CO₂ availability. A major player in carbon and energy metabolism is nitrogen (N) assimilation and some previous studies have shown that AOX gene expression is dependent upon N source and/or N availability. To critically evaluate the functional importance of AOX during N assimilation, wild-type (WT) Nicotiana tabacum were compared to transgenic AOX knockdown (RI9, RI29) and overexpression (B7, B8) lines. Plants were grown hydroponically in growth chambers at three different N concentrations (100µm, 1mM, 5mM), and with N being supplied as either Ca(NO₃)₂ or (NH₄)₂SO₄. RT-qPCR analyses showed that expression of Aox1a (the major stress-responsive AOX gene family member) in WT leaf increased with declining N concentration, and was higher during growth on ammonium than nitrate. The shoot:root dry weight ratio of plants declined with decreasing N concentrations and was higher during growth on nitrate than ammonium, but never differed across the five plant lines. Gas exchange and chlorophyll a fluorescence analyses showed that photosynthetic performance did not differ across plant lines under any of the N conditions. All lines also showed similar rates of dark and light respiration across treatments, and similar expression levels of key mitochondrial proteins. Interestingly, Chl a/b ratio tended to decline at higher nitrate concentrations but the opposite was seen during growth on ammonium. Further, during growth on nitrate, the Chl a/b ratio tended to increase as AOX amount increased across the five plant lines. However, during growth on ammonium, the Chl a/b ratio tended to increase as AOX amount declined across lines. Experiments are underway to determine whether the differences in Chl a/b ratio across plant lines and treatments is due to photosystem stoichiometry adjustments, and whether these adjustments underpin the similar photosynthetic performance of the plant lines, despite their differences in AOX amount. Experiments are also underway to intensify the N treatments through more severe N limitation or higher ammonium concentrations.

1 - University of Toronto, Cell and Systems Biology, 1265 Military Trail, Toronto, ON, M1C 1A4, Canada
2 - University of Toronto, Biology, 1265 Military Trail, Toronto, ON, M1C 1A4, Canada
3 - University of Toronto, Cell and Systems Biology, Biology, 1265 Military Trail, Toronto, ON, M1C 1A4, Canada

Keywords:
Nitrogen Assimilation
Alternative Oxidase
Respiration.

Presentation Type: Oral Paper:Papers for Topics
Session: 20
Location: Salon 13/14/The Shaw Conference Centre
Date: Monday, July 27th, 2015
Time: 2:45 PM
Number: 20005
Abstract ID:703
Candidate for Awards:CSPB President's Award for Best Student Presentation