Peroxidases and photosynthetic pigments in susceptible potato infected with potato virus YNTN

The aim of this work was to investigate the activity of soluble, ionically- and covalently-bound peroxidases (EC 1.11.1.7), the protein content, and the photosynthetic pigment metabolism in the potato (Solanum tuberosum L.) cv. Igor, at the time of local lesion development resulting from infection with potato virus YNTN. In comparison to intact plants, mock inoculation with the sap of healthy plants induced changes in peroxidase activity and metabolism of photosynthetic pigments which could, in most cases, be distinguished from the changes induced by virus infection. An inverse correlation was observed between chlorophyll content and the activity of soluble and ionically-bound peroxidases. This activity increased while that of covalently-bound peroxidase decreased, even in green leaves of infected plants which were visibly unchanged, as well as in green leaves with local lesions. Lower chlorophyll content, and higher carotenoid to chlorophyll ratio than those in intact and mock-inoculated controls – signs of senescence – were observed in leaves with local lesions and in yellow leaves of infected plants. Differences in measured parameters in intact, mock-inoculated, and infected plants showed that processes induced by virus infection differ from those induced by mock inoculation, and that viral induced senescence is clearly not the same as natural senescence.