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 t he N gene for resistance to tobacco mosaic virus, with tobacco mosaic virus induced systemic resistance to Peronospora tabacina and a system ic accumulation of cell wall hydroxyproline. Hydroxyproline increased significantly 12 days after induction with tobacco mosaic virus, and m ore so after challenge with P. tabacina. During this period, hydroxypr oline levels in the control plants remained unchanged. Four salt-solub le cell wall proteins were systemically induced. These proteins were n ot beta-1,3-glucanases, chitinases, or hydroxyproline-rich glycoprotei ns. Light microscopy showed that blue mold development in the induced plants was severely restricted 2 days after challenge; some fungal hyp hae were disorganized near the center of infection sites, and adjacent host cells were plasmolyzed and a few collapsed 3 days after challeng e. All infection sites in the induced plants were associated with necr otic 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 ch aracteristics of induced resistance.