Abstract

The Rhodophyta Gracilaria chilensis is a structuring species of the estuarine and fjord systems in southern Chile and commercially exploited from natural and farmed populations. Due to its capacity to tolerate extreme variations in the environmental conditions this species is an excellent model organism to examine stress tolerance mechanisms in changing environments. The present study examined the combined effect of temperature and UV radiation on the reproductive phases the G. chilensis (carposporophyte, tetrasporophyte and vegetative) at the lower and upper intertidal of the Valdivia River estuary. Concentration of phenolic compounds and their antioxidant capacity as well as the inhibition of primary photochemical reactions, measured as fluorescence of PSII, were determined. Kinetics of maximal quantum yield (Fv/Fm) between 5 and 50 ºC indicated a rapid decrease of photosynthesis from 35 ºC upwards in the three reproductive phases. Exposures for 1, 6, 24 y 48 h to PAR and PAR + UV at 5, 25 and 35°C affected photosynthesis in the three reproductive phases, especially at elevated temperature of 35°C where maximum cumulative decreases of Fv/Fm were close to 93 and 98 % in tetrasporophytes and carposporophytes. An important finding was the high content of phenols, which increased with increasing UV doses only at 10 ºC, especially in carposporophytic and vegetative thalli. Similarly, the antioxidant activity increased in algae exposed to UV radiation at this temperature. In contrast, low (5°C) and elevated (35ºC) temperatures resulted in inhibition of antioxidant activity. Overall the study revealed that the different life history phases of G. chilensis shown similar stress tolerance mechanisms, which appeared to be triggered strongly by temperature and less by UV radiation