Impact of temperature on UV-susceptibility of two Ulva (Chlorophyta) species from Antarctic and Subantarctic regions

The interactive effects of UV-B-exposure and increased temperature were investigated in the two green macroalgae Ulva bulbosa from Antarctica and Ulva clathrata from southern Chile in the laboratory. At seawater temperatures of 0 degrees C, UV-induced inhibition of photosynthesis was much larger in U. clathrata than in U. bulbosa, whereas temperatures of 10 degrees C compensated UV-effects in both species. Despite pronounced photoinhibition, damage to D1 protein in photosystem II could not be detected, indicating that photosynthetic reaction centers were unaffected by experimental UV-exposure. In addition, marked differences in the generation of oxidative stress were not detected. Under all treatments, the activity of superoxide dismutase was higher in U. bulbosa than in U. clathrata, indicating a higher degree of cold adaptation in U. bulbosa from Antarctica, resulting in a higher UV-tolerance at 0 degrees C than in U. clathrata from southern Chile.