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Partitioning of respiratory electrons in the dark in leaves of transgenic tobacco with modified levels of alternative oxidase


  • Robert D. Guy,

    Corresponding author
    1. Department of Forest Sciences, University of British Columbia, 2424 Main Mall, Vancouver, BC, Canada V6T 1Z4
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  • Greg C. Vanlerberghe

    1. Department of Life Sciences and Department of Botany, University of Toronto at Scarborough, 1265 Military Trail, Scarborough, ON, Canada M1C 1A4
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  • Edited by P. Gardeström



This study examined tobacco (Nicotiana tabacum cv. Petit Havana SR1) leaf respiration in the dark, utilizing both wild-type plants and transgenic plants with increased or decreased levels of alternative oxidase (AOX) protein. AOX represents a non-energy-conserving branch in mitochondrial electron transport. Inhibitor studies showed that the maximum possible flux of electrons to AOX (AOX capacity) correlated with the level of AOX protein present in the different plant lines. A comparison of the plants using online 18O isotope discrimination was done to determine whether AOX protein level would impact the actual steady-state partitioning of electrons to AOX (AOX engagement). Under a range of pretreatment and measurement conditions, there was little if any effect of AOX protein level on the degree of engagement. This suggests that the metabolic conditions inherent to a particular growth condition and/or the biochemical regulatory properties of AOX itself are the critical factors that control partitioning. Interestingly, we found that measurement temperature and water status are parameters that may have some influence over AOX engagement.