Journal Article

Deactivation of Photosynthetic Activities is Triggered by Loss of a Small Amount of Water in a Desiccation-Tolerant Cyanobacterium, <i>Nostoc commune</i>

Manabu Hirai, Ruriko Yamakawa, Junko Nishio, Takaharu Yamaji, Yasuhiro Kashino, Hiroyuki Koike and Kazuhiko Satoh

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 45, issue 7, pages 872-878
Published in print July 2004 | ISSN: 0032-0781
Published online July 2004 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pch094
Deactivation of Photosynthetic Activities is Triggered by Loss of a Small Amount of Water in a Desiccation-Tolerant Cyanobacterium, Nostoc commune

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Changes in photosynthetic activities under hypertonic conditions were studied in a terrestrial, highly desiccation-tolerant cyanobacterium, Nostoc commune, and in some desiccation-sensitive cyanobacteria. The amounts of water sustained in the colony matrix outside the N. commune cells and the cellular solute concentration were estimated by measuring the water potential, and the solute concentration was supposed to correspond to around 0.22 M sorbitol. Incubation of the colonies in 0.8 M sorbitol solution inhibited the energy transfer from the phycobilisome (PBS) anchor to PSII core complexes. At higher sorbitol concentrations, light energy absorbed by PSI, PSII, and PBS was dissipated to heat. PSI and cyclic electron flow around PSI was also deactivated by hypertonic treatment. Fv/Fm and (Fm′–F)/Fm′ values started to decrease at 0.6 and 0.3 M sorbitol and reached zero at 1.0 and 0.8 M, respectively. Decreases in these two fluorescence parameters corresponded to the decreases in PSII fluorescence (F695) and photosynthetic CO2 fixation, respectively. The intensity of delayed light emission started to decrease at 1.0 M sorbitol and became negligible at 4.0 M. Comparing these changes in N. commune with those in desiccation-sensitive species, we found that N. commune cells actively deactivates photosynthetic systems on sensing water loss.

Keywords: Keywords: Desiccation tolerance — Hypertonic treatment — Nostoc commune — Photosystem I — Photosystem II — Terrestrial cyanobacterium.; Abbreviations: 2,6-DCBQ, 2,6-dichloro-p-benzoquinone; DLE, millisecond delayed light emission; Fo and Fm, minimum and maximum levels of Chl fluorescence in the dark-adapted samples, respectively; Fm′ and F, maximum and steady state levels of Chl fluorescence in samples illuminated with actinic light, respectively; Fv, a variable part of Chl fluorescence (Fv = Fm – Fo); LCM, a core-membrane linker peptide; P700, a reaction center Chl dimer of PSI; PBS, phycobilisome.

Journal Article.  4248 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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