Oxidase activities during the hypersensitive reaction of Nicotiana xanthi to tobacco mosaic virus.

When plant cells die as a result of virus infection, the activity of oxidases, particularly polyphenoloxidases and peroxidases, is altered (Martin, 1958; Farkas, Kiraly & Solymosy, 1960; Farkas et al. 1964). The in vitro activity of these two enzyme groups in extracts of infected leaves kept at 20° shows changes that are correlated with the time of appearance and number of local lesions. With most virus/host combinations, the oxidase concentration is merely increased (Van Kammen & Brouwer, 1964; Novacky & Hampton, 1968; Cabanne, Scalla & Martin, 1968), with some there is a change in the relative amount of different isozymes (Bates & Chant, 1970), and with others there is possibly the appearance of new peroxidases (Farkas & Stahmann, 1966) or of a new phenolase (John & Weintraub, 1967). Different workers have interpreted these facts to explain the formation of necrosis and virus localization in different ways (Farkas et al. 1960; Parish, Zaitlin & Siegel, 1965; Suseno & Hampton, 1966).