A higher concentration of H2O2 was detected in the sense transgenic potato plant (SS4) with the lily chCu,ZnSOD sequence, whereas higher levels of O2(-) was detected in the antisense transgenic plant (SA1) than the WT plant. The elongation growth in SA1 was significantly inhibited by treatment with diphenyleneiodonium, an inhibitor of O2(-) generation, and promoted in the SS4 on treatment with herbicide methyl viologen, a generator of apoplastic O2(-) . Higher concentrations of GAs were detected during plant growth and the early stage of tuberization in SA1. Complete recovery of the above elongation growth and microtuberization pattern in transgenic plants following treatment of GA(3) or an inhibitor of gibberellin synthesis, paclobutrazol, indicate that these changes were mainly caused by active GA levels. In conclusion, a specific ROS (O2(-) ) acts as a signal transducer via GA biosynthetic pathways for the regulation of plant growth and tuber development of potato.