Relative transcript levels of PPO genes in transgenic potato tuber tissues. (A) Transgenic lines of series amiRPPO1. (B) Transgenic lines of series amiRPPO3. (C) Transgenic lines of series amiRPPO23. (D) Transgenic lines of series amiRPPO234A. (E) Transgenic lines of series amiRPPO1234. Each column represents the mean value obtained from qRT-PCR performed in triplicate on each biological sample. The bars indicate standard deviation. Two biological replicates (indicated as a and b) from each transgenic line were selected for the assay. Cyclophilin and ef1α genes were used as normalization references and non-transgenic potatoes (WT) were set as the control.