INFLUENCE OF SALINITY AND TEMPERATURE ON GROWTH AND PHOTOSYNTHESIS IN THE EXTREMOPHILIC CHLOROPHYTE,NANNOCHLORIS SP. |
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Abstract: | Major, K. M. & Henley, W. J. Department of Botany, Oklahoma State University, Stillwater, OK 74078-3013 USA Preliminary data suggest Nannochloris sp., isolated from the Great Salt Plains National Wildlife Refuge, is a true extremophile. This alga is able to withstand salinities ranging from 0 to 150 ç and temperatures up to 45°C. To test the hypothesis that acclimation to high salinity confers tolerance to high temperature, experimental cultures were acclimated to salinities of 25 and 100 ç and/or temperatures of 23 and 38°C; irradiance (500 mol photons m-2 s-1) was saturating for both growth and photosynthesis. Cells acclimated to low salt and low temperature exhibited high photosynthetic performance in terms of both light-saturated photosynthesis (Pmax; 45.0 fmol O2 cell-1 h-1) and light-harvesting efficiency (0.103 fmol O2 cell-1 h-1/mol photons m-2 s-1). However, high-salinity cells exhibited values for net Pmax (18.1 fmol O2 cell-1 h-1), (0.107 fmol O2 cell-1 h-1/mol photons m-2 s-1) and growth rates (ca. 0.4 d-1) that were equal to, or higher than, those of low-salinity cells when acclimated to high temperature. Both the amount of light required to achieve net photosynthesis (Ic) and that required to achieve light-saturated photosynthesis (Ik) were lower in high-salinity cells than those exhibited by low-salinity cells grown at high temperature; reductions in Ic and Ik were primarily due to increases in light-harvesting efficiency. We propose that an increase in growth temperature might release Nannochloris sp. from energy constraints associated with osmolyte production and low-temperature effects on enzyme activity. These data are consistent with effects of short-term temperature stress on Chl a fluorescence kinetics in this alga. |
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