Manganese superoxide dismutase(MnSOD)and catalase(CAT)are key enzymes in the antioxidant system and important indicators in the resistance study of plants.In this paper,partial cDNA fragments of MnSOD and CAT genes were cloned,and their expression patterns in response to different temperatures and salicylic acid concentrations were investigated by real-time quantitative PCR technique in macroalga Ulva prolifera(Chlorophyta).The cloned MnSOD cDNA was 318 bp,which encoded 105 amino acid residues.The putative MnSOD amino acid sequence of U.prolifera shared 89% identity with that of U.fasciata.Total 229 bp CAT cDNA was obtained,which showed 99% identity with that of U.fasciata,and 93% identity with that of Haematococcus pluvialis by Blast analysis.The phylogenetic trees suggested that U.prolifera clustered with that of U.fasciata in the tree constructed with MnSOD amino acid sequences;and U.prolifera also clustered with U.fasciata firstly,and then clustered with H.pluvialis and Chlamydomonas reintmrdtii in the tree constructed with CAT amino acid sequences.The expression of MnSOD and CAT genes varied in response to different temperatures,of which high temperature showed the most significant effect on the two genes' expression.The expression of MnSOD and CAT was 2.18-fold and 2.05-fold in 35 ℃ culture condition compared with that at 25 ℃,respectively.The expression of MnSOD and CAT was 1.47-fold and 1.31-fold up-regulated at 5 ℃ compared with that at 25 ℃,respectively.However,the expression levels of the two genes in 15 ℃ and 25 ℃ culture conditions showed no significant difference.Salicylic acid is one of plant hormones,which not only played an important role in the growth and development in plants,but also showed key roles in the biotic and abiotic stress resistance.In this macroalga U.prolifera cultured at 35 ℃,0.1 mmol/L salicylic acid promoted expression of MnSOD and CAT mRNA to 2.08 times and 5.30 times that of the control groups.But the expression levels of MnSOD and CAT mRNAs showed no significant difference from the controls when 0.01 mmol/L salicylic acid was added.In conclusion,the expression levels of MnSOD and CAT mRNAs enhanced in response to high or low temperatures.And the expression enhancement of the two genes was also one way of salicylic acid to alleviate the adverse effect caused by high temperature stress in U.prolifera.