Photosynthesis and Respiration under Low Temperature Stress in Two Dunaliella Strains

The photosynthetic and respiratory behaviors of two Dunaliella salina strains (IR-1 and Gh-U) were investigated at two temperature treatments and two assay temperatures. Net photosynthetic rate (P ), photonN saturated net photosynthetic rate (P ), irradiance required to Saturate Photosynthetic (SI), respiration and Nmax pigment changes in D. salina strains, containing different chlorophyll (Chl) contents, shifted from 28 to 13°C for 24 h were compared with controls kept at 28°C, at two assay temperatures (28 and 13°C). Cold stress produced a decrease in total Chl content of IR-1 (higher Chl strain) whereas, Gh-U (lower Chl strain) did not exhibit significant changes under low temperature condition in total Chl. Carotenoid showed a larger decrease in IR-1 compared to that in Gh-U under treatment conditions. P , P , SI and respiration rate were higher in IR-1 N Nmax than those in Gh-U, which had a higher carotenoid/total chlorophyll ratio than IR-1, at all conditions. Transferring the cells to low temperature affected P , P , SI and respiration decreasingly in both strains with N Nmax a larger decrease in P and SI in IR-1, when measuring the photosynthesis and respiration carried out at 13°C. Nmax Both strains exhibited an increase in P and respiration when chilled samples assayed at 28°C. N