• Evergreen conifers in boreal forests can survive extremely cold (freezing) temperatures
    during long dark winter and fully recover during summer. A phenomenon called “sustained
    quenching” putatively provides photoprotection and enables their survival, but its precise
    molecular and physiological mechanisms are not understood. To unveil them, here we have
    analyzed seasonal adjustment of the photosynthetic machinery of Scots pine (Pinus sylvestris)
    trees by monitoring multi-year changes in weather, chlorophyll fluorescence, chloroplast
    ultrastructure, and changes in pigment-protein composition. Analysis of Photosystem II and
    Photosystem I performance parameters indicate that highly dynamic structural and functional
    seasonal rearrangements of the photosynthetic apparatus occur. Although several mechanisms
    might contribute to ‘sustained quenching’ of winter/early spring pine needles, timeresolved
    fluorescence analysis shows that extreme down-regulation of photosystem II
    activity along with direct energy transfer from photosystem II to photosystem I play a major
    role. This mechanism is enabled by extensive thylakoid destacking allowing for the mixing of
    PSII with PSI complexes. These two linked phenomena play crucial roles in winter acclimation
    and protection.

  • Umeå Plant Science Centre, Department of Plant Physiology, Umeå University, Umeå, Sweden



    Copyright: © The Author(s) 2020, corrected publication 2021

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