PRITCHARD, Justin/R; BOETTCHER, Anne; MAJOR, Kelly; University of California Los Angeles and University of South Alabama; University of South Alabama; University of South Alabama: effects of salinity on physiological and molecular responses in extremophilic green algae
Members of the green algal genus, Dunaliella, exhibit broad environmental tolerance. To investigate the effects of salinity on physiological and molecular responses in Dunaliella tertiolecta and Dunaliella salina , we compared algae grown in native salinities (32 and 50 psu, respectively) to those acclimated to either 25 or 100 psu. The two species responded differently to changes in salinity. Cultures of both species exhibited rapid increases in cell density under moderate conditions. However, cultures of D. tertiolecta grown at 32 psu exhibited higher cell densities than any other cultures, regardless of salinity. Salinity had no effect on net light-saturated photosynthesis (Pmax; 500 mmol photons m-2 s-1) in D. tertiolecta. When acclimated to 25 psu, D. salina cells exhibited rates of net photosynthesis that were significantly lower than those grown at 50 psu. Differences in growth and photosynthetic rates were paralleled by differences in expression of heat shock protein 70 (HSP 70). D. tertiolecta expressed two isoforms of HSP 70, one with a nominal molecular size of 77 kDa and one of 79 kDa. High salinity led to significant induction of both isoforms in this alga. D. salina expressed three isoforms of HSP 70 (69, 77 and 79 kDa). A significant induction of the 69 kDa isoform occurred in response to high salinity, while significant induction of the 77 and 79 kDa isoforms occurred in response to low salinity. Differences in responses between species may reflect trade-offs in energetic costs associated with mechanisms of salt tolerance.
