Plant and Cell Physiology Advance Access originally published online on September 30, 2007
Plant and Cell Physiology 2007 48(11):1548-1557; doi:10.1093/pcp/pcm124
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Responses to Desiccation Stress in Bryophytes and an Important Role of Dithiothreitol-Insensitive Non-Photochemical Quenching Against Photoinhibition in Dehydrated States
Department of Life Science, School of Life Science, University of Hyogo, Harima Science Garden City, Hyogo, 678-1297 Japan
*Corresponding author: E-mail, rl05u006{at}stkt.u-hyogo.ac.jp; Fax, +81-791-58-0185.
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Abstract |
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The effects of air drying and hypertonic treatments in the dark on seven bryophytes, which had grown under different water environments, were studied. All the desiccation-tolerant species tested lost most of their PSII photochemical activity when photosynthetic electron transport was inhibited by air drying, while, in all the sensitive species, the PSII photochemical activity remained at a high level even when photosynthesis was totally inhibited. The PSI reaction center remained active under drying conditions in both sensitive and tolerant species, but the activity became non-detectable in the light only in tolerant species due to deactivation of the cyclic electron flow around PSI and of the back reaction in PSI. Light-induced non-photochemical quenching (NPQ) was found to be induced not only by the xanthophyll cycle but also by a 
pH-induced, dithiothreitol-insensitive mechanism in both the desiccation-tolerant and -intolerant bryophytes. Both mechanisms are thought to have an important role in protecting desiccation-tolerant species from photoinhibition under drying conditions. Fluorescence emission spectra at 77K showed that dehydration-induced quenching of PSII fluorescence was observed only in tolerant species and was due to neither state 1–state 2 transition nor detachment of light-harvesting chlorophyll protein complexes from PSII core complexes.The presence of dehydration-induced quenching of PSI fluorescence was also suggested.
Keywords: Bryophyte - Desiccation tolerance - Hypertonic treatment - Non-photochemical quenching - PSII - Xanthophyll cycle
Abbreviations: CCCP, carbonyl cyanide m-chlorophenylhydrazone; DTT, dithiothreitol; Fo and Fm, minimum and maximum level of Chl fluorescence in the dark-adapted samples, respectively; Fm' and F, maximum and steady-state level of Chl fluorescence in samples illuminated with actinic light, respectively; Fv, variable part of Chl fluorescence (Fv = Fm – Fo); NPQ, non-photochemical quenching; P700, a reaction center Chl dimer of PSI; QA, a primary quinone electron acceptor of PSII.
(Received July 8, 2007; Accepted September 23, 2007)
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