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Abstract Detail

Biotic and abiotic stress

Dahal, Keshav [1], Martyn, Greg [2], Vanlerberghe, Greg [1].

Improved photosynthetic performance during severe drought in Nicotiana tabacum overexpressing a non-energy conserving respiratory electron sink.

Metabolic interactions occur between photosynthesis and respiration. Mitochondrial respiration in the light (RL) can impact the turnover of the adenylate and pyridine nucleotide pools, thus perhaps contributing to the ability of the chloroplast to maintain energy homeostasis. Drought is a condition that may strongly disrupt chloroplast energy homeostasis since stomatal closure limits CO2 availability, hence curtailing Calvin cycle activity. While chloroplasts have several potential means to manage excess reducing power, these mechanisms may become restricted by rates of ATP turnover. Interestingly, the plant mitochondrial electron transport chain includes an alternative oxidase (AOX) that uncouples the consumption of reducing power from ATP synthesis. We have shown previously that AOX1a transcript and protein increases as drought severity increases and that during moderate drought, AOX knockdown lines have lower respiration rates (particularly RL) and a reduced photosynthetic capacity compared to wild-type. In the current work, physiological and biochemical analyses were used to compare respiration and photosynthesis of Nicotiana tabacum wild-type plants with that of transgenic lines overexpressing AOX, under both well-watered and drought stress conditions. With increasing drought severity, AOX overexpression acted to increase RL relative to wild-type. CO2 and light response curves indicated that overexpression also improved photosynthetic performance relative to wild-type, as drought severity increased. This was not due to an effect of AOX amount on leaf water status or on the development of the diffusive limitations that occur during drought. Rather, AOX overexpression dampened photosystem stoichiometry adjustments and losses of key photosynthetic components such as ATP synthase that occurred in the wild-type. The results indicate that AOX amount influences RL, particularly during severe drought, when cytochrome pathway respiration may become increasingly restricted. This in turn impacts chloroplast redox state and influences how the photosynthetic apparatus responds to increasing drought severity. In particular, the development of biochemical limitations to photosynthesis are dampened in plants with increased non-energy conserving RL. Overall, these results highlight the importance of non-chloroplast electron sinks for photosynthesis, and suggest that further increasing the capacity of such sinks may be a useful biotechnological approach to preserve photosynthetic potential during drought. Our studies also support the view that impaired photosynthesis during drought, particularly severe drought, can be due to a combination of both diffusive limitations (CO2 supply) and biochemical limitations. Finally, the results provide an example where AOX respiration is clearly advantageous, it’s “energetically wasteful nature” being outweighed by its contribution to maintaining energy homeostasis in photosynthetic metabolism.

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1 - University of Toronto, Biological Sciences, 1265 Military Trail, Toronto, ON, M1C1A4, Canada
2 - University of Toronto, Cell and Systems Biology, 1265 Military Trail, Toronto, ON, M1C 1A4, Canada

Respiration in the light
Mitochondrial alternative oxidase
Nicotiana tabacum.

Presentation Type: Oral Paper:Papers for Topics
Session: 7
Location: Salon 13/14/The Shaw Conference Centre
Date: Monday, July 27th, 2015
Time: 9:00 AM
Number: 7005
Abstract ID:815
Candidate for Awards:None

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