Tissue Specificity of Tobacco Peroxidase Isozymes and Their Induction by Wounding and Tobacco Mosaic Virus Infection

Peroxidases (EC 1.11.1.7) have been implicated in the responses of plants to physical stress and to pathogens, as well as in a variety of cellular processes including cell wall biosynthesis. Tissue samples from leaf, root, pith, and callus of Nicotiana tabacum were assayed for specific peroxidase isozymes by analytical isoelectric focusing. Each tissue type was found to exhibit a unique isozyme fingerprint. Root tissue expressed all of the detectable peroxidase isozymes in the tobacco plant, whereas each of the other tissues examined expressed a different subset of these isozymes. In an effort to determine which peroxidase isozymes from Nicotiana tabacum are involved in cell wall biosynthesis or other normal cellular functions and which respond to stress, plants were subjected to either wounding or infection with tobacco mosaic virus. Wounding the plant triggered the expression of several cationic isozymes in the leaf and both cationic and anionic isozymes in pith tissue. Maximum enzyme activity was detected at 72 hours after wounding, and cycloheximide treatment prevented this induction. Infection of tobacco with tobacco mosaic virus induced two moderately anionic isozymes in the leaves in which virus was applied and also systemically induced in leaves which were not inoculated with virus.