Low temperature enhances photosynthetic down-regulation in French bean (Phaseolus vulgaris L.) plants

Tsonko Tsonev, Violeta Velikova, Katya Georgieva, Paul F. Hyde, Hamlyn Jones

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    The mechanisms of photosynthetic adaptation to different combinations of temperature and irradiance during growth, and especially the consequences of exposure to high light (2000 µmol m¯² s¯¹ PPFD) for 5 min, simulating natural sunflecks, was studied in bean plants (Phaseolus vulgaris L.). A protocol using only short (3 min) dark pre-treatment was introduced to maximize the amount of replication possible in studies of chlorophyll fluorescence. High light at low temperature (10 °C) significantly down-regulated photosynthetic electron transport capacity [as measured by the efficiency of photosystem II (PSII)], with the protective acclimation allowing the simulated sunflecks to be used more effectively for photosynthesis by plants grown in low light. The greater energy dissipation by thermal processes (lower Fv'/Fm' ratio) at low temperature was related to increased xanthophyll de-epoxidation and to the fact that photosynthetic carbon fixation was more limiting at low than at high temperatures. A key objective was to investigate the role of photorespiration in acclimation to irradiance and temperature by comparing the effect of normal (21 kPa) and low (1·5 kPa) O2 concentrations. Low [O2] decreased Fv/Fm and the efficiency of PSII (FPSII), related to greater PSII down-regulation in cold pre-treated plants, but minimized further inhibition by the mild ‘sunfleck’ treatment used. Results support the hypothesis that photorespiration provides a ‘safety-valve’ for excess energy.
    Original languageEnglish
    Pages (from-to)343-352
    Number of pages10
    JournalAnnals of Botany
    Issue number3
    Publication statusPublished - Feb 2003



    • Phaseolus vulgaris L.
    • Bean
    • Low temperature
    • Photosynthesis
    • Down-regulation
    • High light
    • Sunfleck
    • Chlorophyll fluorescence

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