Physcia semipinnata was exposed to UV-A (352 nm) and visible light (210, 800 and 2000 mW/cm(2)) for 30 min, 1, 2, 24, and 48 h to seek the alterations in the PSII photosynthetic quantum yield, in response to radiation. Chlorophyll a fluorescence did not influence exposure to light, 210, 800 and 2000 mW/cm(2). Significant alterations of the photosynthetic quantum yield ratio occurred in response to increase in UV-A exposure time. The photosynthetic quantum yield ratio decreased in P. semipinnata following exposure to UV-A for 24 and 48 h. The thalli of P. semipinnata treated with 1 mM polyamine were not influenced during the exposure to UV-A for 24 and 48 h. It was also found that exogenously spd added samples had higher chla content than spin and put added samples. In this study, we showed that lipid peroxidation levels between UV-A-treated samples and exogenously polyamine treated samples that were previously exposed to UV-A for 24 and 48 h were significantly decreased. This result is the first record to indicate that external polyamines might have some protective role on photosystem 11 and membrane against UV-A stress. (c) 2007 Elsevier B.V. All rights reserved.