Induced Systemic Resistance to Blue Mold: Early Induction and Accumulation ofβ-1,3-Glucanases, Chitinases, and Other Pathogenesis-Related Proteins (b-Proteins) in Immunized Tobacco

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Abstract
Tobacco plants (burley Ky 14) were immunized against blue mold by stem injections with sporangiospores of the blue mold pathogen, Peronospora tabacina. Enzyme activity assays and western blot analyses indicated that .beta.-1,3-glucanases increased in immunized but not in control plants up to 21 days after stem injection. .beta.-1,3-Glucanases continued to increase in the immunized plants 2 and 6 days after challenge, but in controls comparable levels were detected only 6 days after challenge, when the disease was already extensive. Electrophoretic analyses indicated increases in amounts of several b-proteins in immunized plants prior to challenge. Some b-proteins increased further 2 and 6 days after challenge. Increases in b-proteins were detected in controls only 6 days after challenge. A basal level of chitinases was always detected, but increases in chitinases above this level in immunized plants followed a profile similar to that of .beta.-1,3-glucanases and other b-proteins. It is likely that .beta.-1,3-glucanases, chitinases, and other b-proteins are coordinately regulated in tobacco. The increases in these proteins coincided with the onset of immunization in plants injected with P. tabacina, and the levels were maintained during the period after challenge, when the development of P. tabacina was restricted.

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