RESPONSES OF THE ASCORBATE-GLUTATHIONE CYCLE TO NECROTIC VIRUS-INFECTIONS IN TOBACCO

Malondialdehyde (MDA) levels, and activities of ascorbate peroxidase ( AP), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) were determined in Nicotiana tabacum L. cv. Xanthi-nc infected by tob acco mosaic virus (TMV) and in Nicotiana benthamiana L. infected with tobacco necrosis virus. TMV infections led to considerably increased M DA levels in N. tabacum leaf tissues incubated under light, but less n oticeably in darkness. In virus infected leaves AP activities increase d substantially, while DHAR activities decreased in both plant-virus i nteractions. In TMV infected N. tabacum leaves elevated GR activities were also observed. It is supposed that antioxidative reactions influe nce necrotization and thereby symptom expression in virus infected tob acco plants.