| Summary: | 碩士 === 中國文化大學 === 生物科技研究所 === 96 === ‘Tainug 57 (TN57)’, ‘Tainug 66 (TN66)’, ‘Hsuhsu 18 (HS18)’ were selected for studying antioxidase activities in response to salt stress. Four concentrations of NaCl (0, 150, 300 and 450 mM) were imposed at 0, 24, and 48 h followed by measuring leaf water potential and enzyme activity analysis. The objective of this work was to clone the APX gene. After screening and comparing APX gene sequences at the NCBI database, a degenerate primer sets designed for different type of the APX isoforms were used. The primers amplified the APX cDNA of sweet potato using semi-quantitative RT-PCR method to test the different gene expression of different types of APX isoforms in different tissues of sweet potatoes.
The results show that different antioxidae of genotype was associated with salt stress response. HS18 had significant higher water potential and APX activity at both 24 and 48 h under NaCl treatments compared to control (0 h and 0 mM NaCl treatment). Increased APX activity is involved in hydrogen peroxide-detoxification and provides plants with increased salt stress tolerance. Different tissues from sweet potatoes displayed wide variations in their expression profiles. The highest level of cytosolic APX transcripts was detected in root, stem and leaf at 24 h of NaCl treatment. The completion of APX cDNA was performed using RACE technique. The open reading frame of cDNA clone was 986, 1013, 990 and 1048 base pair long encoding peroxisomal APX1, peroxisomal APX2, stromal APX and thylakoid-bound APX, respectively. A phylogenetic analysis of the deduced amino acid sequence of APX by Neighbor-Joining method indicates that sweet potao APX cDNA is closely related to tomato.
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