1993 Volume 59 Issue 2 Pages 107-113
The changes in the activities of enzymes and proteins that may be involved in localized reactions of cucumber cotyledons to tobacco mosaic virus (TMV) were investigated. The peroxidase (PO) and ribonuclease (RNase) activity of the cotyledons increased with the progress of TMV infection, while no increase was observed in plants systemically infected with cucumber green mottle mosaic virus (CGMMV). A marked increase in PO and RNase activity was also observed in cotyledons in which TMV localization had been weakened by actinomycin D (AMD) treatment. In this case the profiles of peroxidase-acidic isozymes and RNase-acidic isozymes did not change. Little polyphenoloxidase activity was detected in TMV-infected cucumber cotyledons. These enzymes thus do not play an active role in the localization process of TMV. When cucumber cotyledons were infected with tobacco necrotic virus or treated with salicylic acid, two pathogenesis-related proteins (PRps) detectable by electrophoresis were induced in the cotyledons. These two proteins were not detected in the cucumber cotyledons infected with TMV. When the two PRps were induced by salicylic acid treatment of cucumber cotyledons, little change was observed in the amount of TMV and in the diameter of starch-lesions. Therefore the two PRps may not be related to the localization of virus. New induced protein bands (82 kDa and 86 kDa) were detected 24 hr after TMV-inoculation. These proteins disappeared when TMV localization was weakened by AMD treatment or by prior inoculation with zucchini yellow moxaic virus (ZYMV). Thus these proteins seem to be directly related to TMV localization in cucumber cotyledons.
