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
2003
Sane, P.V. | Ivanov, A.G. | Hurry, V. | Huner, N.P.A. | Oquist, G.
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 S2Q(-)A recombination was shifted to higher temperatures, whereas the characteristic temperature of the S2Q(-)B recombination was shifted to lower temperatures in cold-acclimated plants. These shifts in recombination temperatures indicate higher activation energy for the S2Q(-)A redox pair and lower activation energy for the S2Q(-)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 PSIIelectron 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.
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