Research article - Peer-reviewed, 2019
Improved in vivo measurement of alternative oxidase respiration in field-collected pine rootsHenriksson, Nils; Marshall, John; Lundholm, Jonas; Boily, Asa; Boily, Jean-Francois; Nasholm, Torgny
AbstractCellular respiration via the alternative oxidase pathway (AOP) leads to a considerable loss in efficiency. Compared to the cytochrome pathway (COP), AOP produces 0-50% as much ATP per carbon (C) respired. Relative partitioning between the pathways can be measured in vivo based on their differing isotopic discriminations against O-18 in O-2. Starting from published methods, we have refined and tested a new protocol to improve measurement precision and efficiency. The refinements detect an effect of tissue water content (P < 0.0001), which we have removed, and yield precise discrimination endpoints in the presence of pathway-specific respiratory inhibitors [CN- and salicylhydroxamic acid (SHAM)], which improves estimates of AOP/COP partitioning. Fresh roots of Pinus sylvestris were sealed in vials with a CO2 trap. The air was replaced to ensure identical starting conditions. Headspace air was repeatedly sampled and isotopically analyzed using isotope-ratio mass spectrometry. The method allows high-precision measurement of the discrimination against O-18 in O-2 because of repeated measurements of the same incubation vial. COP and AOP respiration discriminated against O-18 by 15.1 +/- 0.3 parts per thousand and 23.8 +/- 0.4 parts per thousand, respectively. AOP contributed to root respiration by 23 +/- 0.2% of the total in an unfertilized stand. In a second, nitrogen-fertilized, stand AOP contribution was only 14 +/- 0.2% of the total. These results suggest the improved method can be used to assess the relative importance of COP and AOP activities in ecosystems, potentially yielding information on the role of each pathway for the carbon use efficiency of organisms.
Published inPhysiologia Plantarum
2019, volume: 167, number: 1, pages: 34-47
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