In this study we examined the role of antioxidant metabolism in in vitro shoot multiplication. We generated transgenic plum plantlets overexpressing the cytsod and cytapx genes in cytosol under the control of the constitutive promoter CaMV35S. Three transgenic lines with up-regulated sod at transcriptional levels that showed silenced cytapx expression displayed an elevated in vitro multiplication rate. By contrast, a transgenic line harboring several copies of cytapx and with elevated APX enzymatic activity did not show any improvement in plant vigor, measured as the number of axillary shoots and shoot length. All of the lines with elevated micropropagation ability exhibited intensive H2O2 accumulation, monitored by 3,3'-diaminobenzidine (DAB) staining as well as by colorimetric analysis, providing direct in vitro evidence of the role of H2O2 and antioxidant genes in in vitro shoot multiplication.
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