The influence of viral infection caused by two different potyviruses, Potato virus Y (PVY) and Potato virus A (PVA) on plant metabolism and photosynthetic apparatus of Nicotiana tabacum L. cv. Samsun and cv. Petit Havana SR1 was studied. The main stress was focused on the activities of phosphoenolpyruvate carboxylase (PEPC), NADP-malic enzyme (NADP-ME), and pyruvate phosphate dikinase (PPDK). The analysis of the presence of viral proteins, enzyme activities, and different photosynthetic parameters showed the time dependent progress of viral infection and NADP-ME and PEPC activities. PVY caused significant response, while PVA affected both tobacco cultivars only slightly. Viral infection, namely PVY, affected more negatively photosynthetic apparatus of cv. Petit Havana SR1 than cv. Samsun.

Ellipticine is a potent antineoplastic agent, whose mode of action is considered to be based mainly on DNA intercalation, inhibition of topoisomerase II and cytochrome P450‐mediated formation of covalent DNA adducts. This is the first report on the molecular mechanism of ellipticine oxidation by peroxidases (human myeloperoxidase, human and ovine cyclooxygenases, bovine lactoperoxidase, horseradish peroxidase) to species forming ellipticine‐DNA adducts. Using NMR spectroscopy, the structures of 2 ellipticine metabolites were identified; the major product is the ellipticine dimer, in which the 2 ellipticine skeletons are connected via N⁶ of the pyrrole ring of one ellipticine molecule and C9 in the second one. The minor metabolite is ellipticine N²‐oxide. Using ³²P‐postlabeling and [³H]‐labeled ellipticine, we showed that ellipticine binds covalently to DNA after its activation by peroxidases. The DNA adduct pattern induced by ellipticine consisted of a cluster of up to 4 adducts. The 2 adducts are indistinguishable from the 2 major adducts generated between deoxyguanosine in DNA and either 13‐hydroxy‐ or 12‐hydroxyellipticine or in rats treated with ellipticine, or if ellipticine was activated with human hepatic and renal microsomes. The results presented here are the first characterization of the peroxidase‐mediated oxidative metabolites of ellipticine and we have proposed species, 2 carbenium ions, ellipticine‐13‐ylium and ellipticine‐12‐ylium, as reactive species generating 2 major DNA adducts seen in vivo in rats treated with ellipticine. The study forms the basis to further predict the susceptibility of human cancers to ellipticine.