CONSEQUENCES OF PHOTOOXIDATION IN TRANSGENIC TOBACCO WITH CO-SUPPRESSION OF COPROPORPHYRINOGEN OXIDASE

Introduction of additional copies of genes encoding coproporphyrinogen oxidase (CPO) caused in some transgenic lines necrotic leaf lesions. As a result of mutual silencing of transgenes and endogenous genes CPO activities were reduced and photosensitive coproporphyrin(ogen) accum ulated. Photo-oxidation of these porphyrins generated reactive oxygen species which induced the protection mechanism against oxidative stres s. Activities of ascorbate peroxidase, glutathione reductase and super oxide dismutase were increased in these transgenic lines. We conclude that these plants accumulating porphyrin are appropriate for studies o n the induction mechanisms of the antioxidative defense system.