PEROXIDASE-ACTIVITY AND ISOPEROXIDASE PATTERN IN TOBACCO-LEAVES INFECTED WITH TOBACCO NECROSIS VIRUS AND OTHER VIRUSES INDUCING NECROTIC AND NON-NECROTIC ALTERATIONS

The level of peroxidase activity was greatly enhanced in tobacco leave s infected by tobacco necrosis virus (TNV) and other viruses which ind uce necrotic symptoms (TMV, ToMV and PVYN). The intensity was related to the age of the leaves infected: absent or negligible in mature leav es and very pronounced in young growing infected leaves. On the contra ry, changes in peroxidase activity were negligible when the infection was provoked by viruses which do not produce necrotic reactions (TMV a nd PVYO). Analysis of the peroxidase isoenzyme pattern in tobacco leav es infected by TNV and other necrosis-inducing viruses revealed in all cases, a slight increase in anionic (pI 3.5-3.7) and a considerable i ncrease in moderately anionic isoenzymes, particularly the pI 4.6 isoe nzyme which in TNV and PVYN-infected leaves reached levels up to 21 an d 72 times the healthy control values. A considerable increase in the cationic (pI 9.3-8.8) isoenzymes and the appearance of one moderately cationic isoenzyme (pI 8.2) was also detected. In leaf extracts from v irus-infected tobacco leaves with nonnecrotic response, no, or negligi ble alterations on the isoenzyme pattern were detected. However, infec tion by a fungal parasite (Erisyphe cichoracearum), which established a fully compatible, non-necrotic, interaction with tobacco leaves, lik e the necrosis-inducing viruses, changed the isoperoxidase pattern. Th e data suggest the necrotic alterations and associated changes in the peroxidase activity and isoperoxidase pattern in virus-infected leaves are not clearly related.