N-acetylcysteine-dependent protection against UV-B damage in two photosynthetic organisms

Cellular thiols, specially glulathione, appear to play a key role in protection against oxidative damage arising from a number of stress conditions. Thus, the role of N-acetylcysteine (NAC) as a protector against oxidative damage associated with ultraviolet B (UV-B) in two photosynthetic organisms was evaluated. Algal cultures (Chlorella vulgaris) and soybean leaves (Glycine max var. Hood) were supplemented with 1 mM NAC before irradiation. The content of total thiols was significantly increased after treatment. After exposure to W-B, the ascorbyl radical-dependent electron paramagnetic resonance (EPR) signal was enhanced by 76 and 46% and lipid radical-dependent EPR signal increased by 83 and 188% in algal cultures and soybean leaves, respectively. Treatment with 1 mM NAC kept ascorbyl and lipid radical content in algae and soybean leave exposed to UV-B at the basal level. Supplementation with 1 mM NAC did not affect the content of lipid-soluble antioxidants (alpha-tocopherol, beta-carotene) in C. vulgaris or in soybean leaves. UV-B irradiation increased catalase activity in the algae by 145% and in soybean leaves by 34%, while total superoxide dismutase (SOD) activity was not affected. In both photosynthetic organisms the increase in catalase activity after UV-B exposure did not occur in the presence of 1 mM NAC. The results suggest that thiols play an important role in triggering cellular control against UV-B-related damage, as NAC pretreatment significantly decreased UV-B-dependent radical generation after irradiation. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.