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Articles

Cell Wall and Protoplast Isoperoxidases in Tobacco Plants in Relation to Mechanical Injury and Infection with Tobacco Mosaic Virus

Paul Urban²

¹ Department of Biological Sciences, Union College, Schenectady, New York 12308, ² Electron Microscopy Laboratory, Veterans Administration Hospital, Albany, New York 12208

Leaves and pith of Turkish, Wisconsin 38, and Samsun NN tobacco (Nicotiana tabacum) varieties, which differ in their sensitivity to tobacco mosaic virus, showed the same qualitative isoperoxidase patterns and a similar distribution of distinctive isoperoxidases between the cell protoplast and wall-free, ionically, and covalently bound fractions. No changes in the qualitative isoenzyme spectrum were found in relation to age, mechanical injury, or leaf infection with tobacco mosaic virus. The distinctive isoperoxidases which reacted to infection were the same as those responsive to mechanical injury, confirming that the enzyme reaction to infection results from a nonspecific response to injury. The increase in peroxidase activity in response to infection or mechanical injury, or both, was greater in young tissue than in the older ones. The great increase in Samsun NN leaves and no increase in those of the two other varieties in response to infection may be due to differences in the degree to which the pathogen affected processes controlling the nonspecific peroxidase reaction to injury. Peroxidase development in the infected Samsun NN leaves was due to isoenzymes which form the wall-bound fraction in very young tissues, and to those which increase in activity with aging in the protoplast and wall-free fractions. In mechanically injured tissue, only the first group of isoenzymes increased in activity. In Samsun NN plants, the increased peroxidase activity in upper intact leaves above the infected ones was only due to isoenzymes whose activity increases with both normal and virus-accelerated senescence. Peroxidase reaction to challenge inoculation in these leaves was the same whether the lower ones were intact, infected and/or mechanically injured. Thus, the induced systemic resistance to tobacco mosaic virus may be due to other than peroxidase factors.

In infected tissues, peroxidase was detected in the endoplasmic reticulum, Golgi apparatus, vacuole, cell wall, and intercellular spaces. The Golgi vesicles were often localized near the tonoplast and plasmalemma, fusing with membranes and secreting their contents. The possible "rejuvenating" effects of injury on synthesis and transport of distinctive isoperoxidases are discussed.