| Summary: | Progress Code: completed Statement: Taken from the 2005-2006 Progress Report: This objective will be met by addressing the following questions: 1) How does light and temperature stress interact in relation with the photosynthesis of sea-ice algae? - Do all species partition photon energy in a similar way between photochemical quenching (qP) and non-photochemical quenching (qN) when exposed to light and temperature stress? 2) Does low temperature exacerbate light stress in sea-ice algae? - Do changes in temperature of these cryophilic cells cause the photosystems to alter their efficiency and therefore become photoinhibited? - Does the composition and organisation of PSII apparatus change with cold acclimation? 3) How do sea-ice algae use energy dissipation pathways to protect themselves? - Do sea-ice algae use non-photochemical quenching as a permanent energy dissipation mechanism, as opposed to a dynamic photoprotective mechanism? - Does light and/or temperature stress correlate with particular components of non-photochemical quenching processes (qE/qT/qI)? - Does state-transition quenching increase at lower temperatures? 4) Do sea ice algae use alternate protective mechanisms, apart from qN? - How important is PSI cyclic electron transport (Mehler) and photorespiration in low temperature stress? Approach: Experiment 1: Partitioning of quenching under light/temperature manipulations Photosynthesis of sea-ice algae is strongly influenced by light and temperature (Rochet et al 1985; Palmisano et al 1987). At low temperatures the photosynthetic apparatus (enzyme systems) functions slowly, so light can easily damage the photosystems due to the formation of free radicals. All plants attempt to achieve photostasis, where incoming photon energy is carefully balanced between maximising photosynthesis, without allowing excess energy to cause damage to the photosystems. As such, energy absorbed from irradiance can be used in photosynthesis (photochemical quenching, qP) or protectively dissipated as excess heat ...
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