Two parthenogenetic populations of Chara canescens differ in their capacity to acclimate to irradiance and salinity.

The parthenogens of Chara canescens (Charophyceae) occupy broader geographical and ecological ranges than their sexual counterparts. Two possible hypotheses explain the ubiquity of parthenogens: the occurrence of one or several parthenogens with wide niches, or of many parthenogens that are restricted to narrow ecological niches. For the purposes of this study, C. canescens individuals from two neighbouring populations of the Baltic Sea (Bodstedter Bodden = BB; Salzhaff = SH), which differed significantly in water transparency and salinity, were investigated for significant differences in physiological capacity. Individuals of both habitats acclimated quickly to daily changes in irradiances in the field, but the photosynthetic efficiency of PS II showed a significant decrease with increasing daily irradiance in the habitat BB, which has lower levels of salinity and water transparency. In addition to the field study, individuals were reared under different levels of environmental factors in the laboratory: four irradiances (70-600 µmol m(-2) s(-1)) and five salinity levels (0-24 psu). The individuals of both habitats grew almost equally well at intermediate salinity levels. Growth under the artificial light supply was highest at levels corresponding to the in situ conditions for each population. Total chlorophyll was highest at intermediate salinities (BB), or hardly changed with salinity (SH). The physiological capacity for individuals from SH clearly depends upon changing growth irradiance, whereas the capacity for individuals from BB was relatively independent of salinity and irradiance. These findings indicate that both parthenogenetic C. canescens populations are locally adapted to light. However, to test adaptive potential of the parthenogens, more than two populations should be tested in future.

Stress responses and metal tolerance of Chlamydomonas acidophila in metal-enriched lake water and artificial medium.

Chlamydomonas acidophila faces high heavy-metal concentrations in acidic mining lakes, where it is a dominant phytoplankton species. To investigate the importance of metals to C. acidophila in these lakes, we examined the response of growth, photosynthesis, cell structure, heat-shock protein (Hsp) accumulation, and metal adsorption after incubation in metal-rich lake water and artificial growth medium enriched with metals (Fe, Zn). Incubation in both metal-rich lake water and medium caused large decreases in photosystem II function (though no differences among lakes), but no decrease in growth rate (except for medium + Fe). Concentrations of small Hsps were higher in algae incubated in metal-rich lake-water than in metal-enriched medium, whereas Hsp60 and Hsp70A were either less or equally expressed. Cellular Zn and Fe contents were lower, and metals adsorbed to the cell surface were higher, in lake-water-incubated algae than in medium-grown cells. The results indicate that high Zn or Fe levels are likely not the main or only contributor to the low primary production in mining lakes, and multiple adaptations of C. acidophila (e.g., high Hsp levels, decreased metal accumulation) increase its tolerance to metals and permit survival under such adverse environmental conditions. Supposedly, the main stress factor present in the lake water is an interaction between low P and high Fe concentrations.

Temperature- and pH-dependent accumulation of heat-shock proteins in the acidophilic green alga Chlamydomonas acidophila.

Chlamydomonas acidophila, a unicellular green alga, is a dominant phytoplankton species in acidic water bodies, facing severe environmental conditions such as low pH and high heavy metal concentrations. We examined the pH-, and temperature-dependent accumulation of heat-shock proteins in this alga to determine whether heat-shock proteins play a role in adaptation to their environment. Our results show increased heat-shock proteins accumulation at suboptimal pHs, which were not connected with any change in intracellular pH. In comparison to the mesophilic Chlamydomonas reinhardtii, the acidophilic species exhibited significantly higher accumulations of heat-shock proteins under control conditions, indicating an environmental adaptation of increased basal levels of heat-shock proteins. The results suggest that heat-shock proteins might play a role in the adaptation of C. acidophila, and possibly other acidophilic algae, to their extreme environment.