Biological pathways are complex bio-machinery which is dependent on several interactions and a clear answer to what you are suggesting can not be made. It is more a trial and analysis process. Nevertheless, the Catharanthus TIA pathway suggests that, peroxidase type 1, facilitates the conversion of Catharanthine to intermediate and eventually to Vinblastine/Vincristine. Hence, the first opinion would be supression of PRX1 in this pathway could result in the reduction of intermediate conversion to Vinblastine/Vincristine.