Overexpression of a chloroplast-localized Cu/Zn superoxide dismutase (chCu/ZnSOD) obtained from lily significantly affects the growth and shape of potato tubers from an in vitro culture system (Kim et al., 2007). Here, we further characterized the sense and antisense transgenic potatoes grown and pots and the greenhouse to investigate the potential for more practical field applications of such phenotypic manipulations. Under in vitro conditions, antisense transgenic plants showed increased shoot growth, delayed tuberization, and altered tuber shapes. When antisense plants were treated with paclobutrazol, an inhibitor of GA biosynthesis, tuberization efficiency and tuber shape were recovered to a status very similar to that of in vitrogrown wild-type plants. Our results strongly support the idea that potato tuberization and shape is mediated by SOD-catalyzed reactive oxygen species, possibly via the GA biosynthesis pathway.