BIOCHEMICAL-CHANGES IN CELL-WALLS AND CELLULAR-RESPONSES OF TOBACCO-LEAVES RELATED TO SYSTEMIC RESISTANCE TO BLUE MOLD (PERONOSPORA-TABACINA) INDUCED BY TOBACCO MOSAIC-VIRUS

Inoculation of lower leaves of tobacco cultivar Ky 14, which carries the N gene for resistance to tobacco mosaic virus, with tobacco mosaic virus induced systemic resistance to Peronospora tabacina and a systemic accumulation of cell wall hydroxyproline. Hydroxyproline increased significantly 12 days after induction with tobacco mosaic virus, and more so after challenge with P. tabacina. During this period, hydroxyproline levels in the control plants remained unchanged. Four salt-soluble cell wall proteins were systemically induced. These proteins were not beta-1,3-glucanases, chitinases, or hydroxyproline-rich glycoproteins. Light microscopy showed that blue mold development in the induced plants was severely restricted 2 days after challenge; some fungal hyphae were disorganized near the center of infection sites, and adjacent host cells were plasmolyzed and a few collapsed 3 days after challenge. All infection sites in the induced plants were associated with necrotic cells 5-6 days after challenge. Electron microscopy revealed that damage to fungal hyphae, plasmolysis and shrinking of infected cells, and more electron-opaque host cell walls and wall appositions were characteristics of induced resistance.