The aim of this work was to study the short-term effects of salt stress on the antioxidant system and ascorbate peroxidase (APX) expression in two salt sensitive sweet potato cultivars Tainung 57 (TN57) and Tainung 66 (TN66), and one salt-tolerant cultivar Hsusu 18 (HS18). Plants were grown in plastic pots in a greenhouse for 30 d followed by NaCl treatments (0, 150, 300, and 450 mM) for 0, 24 and 48 h in a growth chamber. Young, fully expanded leaves of each treatment and period of time were clipped for enzyme activity measurements. In addition, different tissues (leaves, stems, and roots) were also harvested to analyze the tissue-specific APX gene expression using semiquantitative reverse-transcription polymerase chain reaction (RT-PCR). Three degenerated primers of APX isoforms from cytosol, peroxisomes and chloroplasts were used to amplify the APX complementary DNA of these cultivars. Our results show higher increase in APX activity at 24 and 48 h of salinity (450 mM of NaCl) in salt-stress tolerant genotype than in saltsensitive ones. The expression of APX isoforms in response to salinity was tissue specific and also dependent on stress duration.Additional key words: antioxidant enzyme, APX isoforms, Ipomoea batatas, RT-PCR.

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