Cell turgor: A critical factor for the proliferation of cyanobacteria at unfavorable salinity |
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Authors: | Nectarios P Ladas George C Papageorgiou |
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Institution: | (1) Institute of Biology, National Center for Scientific Research Demokritos, Athens, Greece, 153 10;(2) Institute of Biology, National Center for Scientific Research Demokritos, Athens, Greece, 153 10 |
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Abstract: | We employed chlorophyll a fluorometry in order to measure the evolution of turgor threshold (intracellular osmolality) during the adaptation of two
genetic transformants of the freshwater cyanobacterium Synechococcus sp. PCC7942 to unfavorable external salinity: PAMCOD cells which oxidize imported choline and accumulate approx. 0.06–0.08
M glycine betaine; and PAM cells which do not oxidize choline Deshnium et al. (1995a) Plant Mol Biol 29: 897–909]. Turgor
thresholds increased linearly (a) with the NaCl concentration in the culture, and (b) with the molar sucrose/chlorophyll a ratio in the cell. PAMCOD cells could proliferate in culture medium containing 0.4 M NaCl (external osmolality, 0.815 Osm
kg−1), after a lag period, during which intracellular sucrose rose to 10 mol (mol Chl a)−1, or more, and turgor threshold (cytoplasmic osmolality) exceeded 1 Osm kg−1. At comparative conditions, PAM cells accumulated approx. half as much sucrose, and attained approx. half as high turgor
thresholds as the PAMCOD cells, but they did not proliferate. These results indicate that glycine betaine improved the salinity
tolerance of the PAMCOD cells synergistically, by means of two effects that implicate sucrose, the main organic osmolyte of
Synechocccus: enhancement of sucrose biosynthesis, and/or alleviation of sucrose toxicity.
This revised version was published online in June 2006 with corrections to the Cover Date. |
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Keywords: | adaptation to salinity cyanobacteria glycine betaine intracellular osmolality osmotic chlorophyll fluorescence quenching sucrose Synechococcus sp PCC7942 |
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