title: Low temperature enhances photosynthetic down-regulation in French bean (Phaseolus vulgaris L.) plants.
abstract: The mechanisms of photosynthetic adaptation to different combinations of temperature and irradiance during growth, and especially the consequences of exposure to high light (2000 micro mol 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 degrees 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 F(v)'/F(m)' 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) O(2) concentrations. Low [O(2)] decreased F(v)/F(m) and the efficiency of PSII (Phi(PSII)), 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.
authors.affiliation: Acad. M. Popov Institute of Plant Physiology, Bulgarian Academy of Sciences, Acad. G. Bonchev Street, Bl. 21, 1113 Sofia, Bulgaria.
authors.forename: Tsonko
authors.initials: T
authors.lastname: Tsonev
authors.forename: Violeta
authors.initials: V
authors.lastname: Velikova
authors.forename: Katya
authors.initials: K
authors.lastname: Georgieva
authors.forename: Paul F
authors.initials: PF
authors.lastname: Hyde
authors.forename: Hamlyn G
authors.initials: HG
authors.lastname: Jones
mesh_terms: D000222:Adaptation, Physiological / Q000528:radiation effects; D002734:Chlorophyll / Q000378:metabolism; D003080:Cold Temperature; D005453:Fluorescence; D027805:Phaseolus / Q000378:metabolism* / Q000528:radiation effects; D010788:Photosynthesis / Q000528:radiation effects; D010860:Pigments, Biological / Q000032:analysis; D013472:Sunlight; D013997:Time Factors
chemical_list: D010860:Pigments, Biological; D002734:Chlorophyll