Deactivation of photosynthetic activities is triggered by loss of a small amount of water in a desiccation-tolerant cyanobacterium, Nostoc commune.
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.
Department of Life Science, Graduate School of Life Science, University of Hyogo (Formerly: Himeji Institute of Technology), Harima Science Garden City, Hyogo, 678-1297 Japan.
Manabu
M
Hirai
Ruriko
R
Yamakawa
Junko
J
Nishio
Takaharu
T
Yamaji
Yasuhiro
Y
Kashino
Hiroyuki
H
Koike
Kazuhiko
K
Satoh
D002245:Carbon Dioxide / Q000378:metabolism; D000458:Cyanobacteria / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D003681:Dehydration / Q000378:metabolism*; D004579:Electron Transport / Q000187:drug effects / Q000235:genetics; D004734:Energy Metabolism / Q000187:drug effects / Q000502:physiology; D006982:Hypertonic Solutions / Q000494:pharmacology; D008027:Light; D009997:Osmotic Pressure / Q000187:drug effects; D010084:Oxidation-Reduction / Q000187:drug effects; D010788:Photosynthesis / Q000187:drug effects / Q000502:physiology*; D014882:Water-Electrolyte Balance / Q000187:drug effects / Q000502:physiology*
D006982:Hypertonic Solutions; D002245:Carbon Dioxide