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°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 Ϫ recombination was shifted to higher temperatures, whereas the characteristic temperature of the S 2 Q B Ϫ 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 Ϫ redox pair and lower activation energy for the S 2 Q B Ϫ redox pair. This results in an increase in the free-energy gap between P680 ϩ Q A Ϫ and P680 ϩ Pheo Ϫ 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 ϩ Q A Ϫ 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.It has been shown previously in winter cereals (Ö quist and Huner, 1993) and Arabidopsis (Strand et al., 1997(Strand et al., , 1999) that cold acclimation results in an increased capacity for photosynthesis at suboptimal temperatures. This recovery in photosynthetic capacity is closely associated with the posttranslational activation and the selective increase in the expression of enzymes involved in Suc synthesis, with changes in expression and activity of Calvin cycle enzymes (Strand et al., 1997(Strand et al., , 1999(Strand et al., , 2003 Hurry et al., 2000; Stitt and Hurry, 2002), and with changes in the lipid composition and the content of unsaturated fatty acids of chloroplast membranes (Raison et al., 1982; Hugly and Somerville, 1992; Moon et al., 1995; Routaboul et al., 2000). These changes in photosynthetic capacity and in chloroplast membrane composition protect the photosynthetic apparatus against photoinhibition at low temperatures by allowing increased turnover of the photosynthetic electron transport chain (Hurry et al., 1993(Hurry et al., , 1995 Huner et al., 1998).However, results obtained with Scots pine (Pinus sylvestris) indicate that cold acclimation can increase the level of photosystem II (PSII) resistance to excessive light directly without any increase in photosynthetic capacity (Krivosheeva et al., 1996). The acquisition of increased tolerance to photoinhibition in cold-acclimated plants has also been ascribed to growth and development under high...

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The Redox Potential of the Plastoquinone Pool of the Cyanobacterium Synechocystis Species Strain PCC 6803 Is under Strict Homeostatic Control

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Minor Antenna Proteins CP24 and CP26 Affect the Interactions between Photosystem II Subunits and the Electron Transport Rate in Grana Membranes of Arabidopsis

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