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.
- Phaseolus vulgaris L.
- Low temperature
- High light
- Chlorophyll fluorescence
Tsonev, T., Velikova, V., Georgieva, K., Hyde, P. F., & Jones, H. (2003). Low temperature enhances photosynthetic down-regulation in French bean (Phaseolus vulgaris L.) plants. Annals of Botany, 91(3), 343-352. https://doi.org/10.1093/aob/mcg020