title: Changes in the redox potential of primary and secondary electron-accepting quinones in photosystem II confer increased resistance to photoinhibition in low-temperature-acclimated Arabidopsis.
abstract: Exposure of control (non-hardened) Arabidopsis leaves for 2 h at high irradiance at 5 degrees C resulted in a 55% decrease in photosystem II (PSII) photochemical efficiency as indicated by F(v)/F(m). In contrast, cold-acclimated leaves exposed to the same conditions showed only a 22% decrease in F(v)/F(m). Thermoluminescence was used to assess the possible role(s) of PSII recombination events in this differential resistance to photoinhibition. Thermoluminescence measurements of PSII revealed that S(2)Q(A)(-) recombination was shifted to higher temperatures, whereas the characteristic temperature of the S(2)Q(B)(-) recombination was shifted to lower temperatures in cold-acclimated plants. These shifts in recombination temperatures indicate higher activation energy for the S(2)Q(A)(-) redox pair and lower activation energy for the S(2)Q(B)(-) redox pair. This results in an increase in the free-energy gap between P680(+)Q(A)(-) and P680(+)Pheo(-) and a narrowing of the free energy gap between primary and secondary electron-accepting quinones in PSII electron acceptors. We propose that these effects result in an increased population of reduced primary electron-accepting quinone in PSII, facilitating non-radiative P680(+)Q(A)(-) radical pair recombination. Enhanced reaction center quenching was confirmed using in vivo chlorophyll fluorescence-quenching analysis. The enhanced dissipation of excess light energy within the reaction center of PSII, in part, accounts for the observed increase in resistance to high-light stress in cold-acclimated Arabidopsis plants.
authors.affiliation: Umeå Plant Science Centre, Department of Plant Physiology, Umeå University, Umeå S-901 87, Sweden.
authors.forename: Prafullachandra Vishnu
authors.initials: PV
authors.lastname: Sane
authors.forename: Alexander G
authors.initials: AG
authors.lastname: Ivanov
authors.forename: Vaughan
authors.initials: V
authors.lastname: Hurry
authors.forename: Norman P A
authors.initials: NP
authors.lastname: Huner
authors.forename: Gunnar
authors.initials: G
authors.lastname: Oquist
mesh_terms: D000064:Acclimatization; D017360:Arabidopsis / Q000378:metabolism*; D003080:Cold Temperature; D004579:Electron Transport; D005453:Fluorescence; D007700:Kinetics; D008027:Light; D045342:Light-Harvesting Protein Complexes; D008564:Membrane Potentials; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D045332:Photosystem II Protein Complex; D018515:Plant Leaves / Q000378:metabolism; D011809:Quinones / Q000378:metabolism*
chemical_list: D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D011809:Quinones