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We evaluated the effect of global warming on Araucaria angustifolia (Bert.) O. Kuntze, a critically endangered native tree of Southern Brazil, by studying the effects of short-term high temperature treatment on cell viability, respiration and DNA repair of embryogenic cells. Compared with control cells grown at 25 degrees C, cell viability was reduced by 40% after incubation at 30 and 37 degrees C for 24 and 6 h, respectively, while 2 h at 40 and 42 degrees C killed 95% of the cells. Cell respiration was unaffected at 30-37 degrees C, but dramatically reduced after 2 h at 42 degrees C. The in vitro activity of enzymes of the base excision repair (BER) pathway was determined. Apurinic/apyrimidine endonuclease, measured in extracts from cells incubated for 2 h at 42 degrees C, was completely inactivated while lower temperatures had no effect. The activities of three enzymes of the mitochondrial BER pathway were measured after 30-min preincubation of isolated mitochondria at 25-40 degrees C and one of them, uracil glycosylase, was completely inhibited at 40 degrees C. We conclude that cell viability, respiration and DNA repair have different temperature sensitivities between 25 and 37 degrees C, and that they are all very sensitive to 40 or 42 degrees C. Thus, A. angustifolia will likely be vulnerable to the short-term high temperature events associated with global warming.