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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Increased Air Temperature during Simulated Autumn Conditions Impairs Photosynthetic Electron Transport between Photosystem II and Photosystem I^1,[OA]

Department of Biology and the BIOTRON, University of Western Ontario, London, Ontario, Canada N6A 5B7 (F.B., N.P.A.H., I.E.); Institute of Chemistry and Dynamics of the Geosphere ICG-II, Phytosphere, Research Center Jülich, 52425 Juelich, Germany (F.B.); and Department of Forest Ecology, Forest Research Institute Baden-Wuerttemberg, 79100 Freiburg, Germany (I.E.)

Changes in temperature and daylength trigger physiological and seasonal developmental processes that enable evergreen trees of the boreal forest to withstand severe winter conditions. Climate change is expected to increase the autumn air temperature in the northern latitudes, while the natural decreasing photoperiod remains unaffected. As shown previously, an increase in autumn air temperature inhibits CO₂ assimilation, with a concomitant increased capacity for zeaxanthin-independent dissipation of energy exceeding the photochemical capacity in Pinus banksiana. In this study, we tested our previous model of antenna quenching and tested a limitation in intersystem electron transport in plants exposed to elevated autumn air temperatures. Using a factorial design, we dissected the effects of temperature and photoperiod on the function as well as the stoichiometry of the major components of the photosynthetic electron transport chain in P. banksiana. Natural summer conditions (16-h photoperiod/22°C) and late autumn conditions (8-h photoperiod/7°C) were compared with a treatment of autumn photoperiod with increased air temperature (SD/HT: 8-h photoperiod/22°C) and a treatment with summer photoperiod and autumn temperature (16-h photoperiod/7°C). Exposure to SD/HT resulted in an inhibition of the effective quantum yield associated with a decreased photosystem II/photosystem I stoichiometry coupled with decreased levels of Rubisco. Our data indicate that a greater capacity to keep the primary electron donor of photosystem I (P700) oxidized in plants exposed to SD/HT compared with the summer control may be attributed to a reduced rate of electron transport from the cytochrome b₆f complex to photosystem I. Photoprotection under increased autumn air temperature conditions appears to be consistent with zeaxanthin-independent antenna quenching through light-harvesting complex II aggregation and a decreased efficiency in energy transfer from the antenna to the photosystem II core. We suggest that models that predict the effect of climate change on the productivity of boreal forests must take into account the interactive effects of photoperiod and elevated temperatures.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Ingo Ensminger (ingo.ensminger{at}ctp.uni-freiburg.de).

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www.plantphysiol.org/cgi/doi/10.1104/pp.108.117598

^* Corresponding author; e-mail ingo.ensminger{at}ctp.uni-freiburg.de.

Received February 9, 2008; accepted March 18, 2008; published March 28, 2008.

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On the Inside

Peter V. Minorsky
Plant Physiol. 2008 147: 1-2. [Full Text]