Specificity of induced systemic resistance as elicited by ethephon and tobacco mosaic virus in tobacco

Abstract

Inoculation of 3–4 leaves of tobacco cv Ky 14 with tobacco virus (TMV) induced systemic resistance to blue mold and TMV but pricking in the presence of ethephon induced systemic resistance to TMV only. Twelve acid-soluble proteins either increased or were detected only in TMV-inoculated leaves by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) as compared to mock-inoculated controls. Most of the proteins were induced locally and systemically by TMV and ethephon, but accumulated levels of some differed. Ten major acidic pathogenesis-related (PR) proteins were systemically induced by TMV. After treatment with ethephon, three of these proteins, PR-2, N and O, were not systemically induced. Ethephon treatment did induce PR-la, b and c, although induction was weak in comparison to that which occured in response to TMV. Two other proteins, EI 1 and EI 2, were induced following treatment with ethephon, but these proteins were not found in TMV-infected leaves. Chitinase and peroxidase activites were systemically and equally enhanced by TMV and ethephon. Seven acidic proteins exhibiting chitinase activities were detected as lytic zones on glycol chitin-containing overlay gels. One chitinase corresponding to PR-P was enhanced locally and systemically after inoculation with TMV or treatment with ethephon. Activities of two highly anionic peroxidases were systemically increased after TMV inoculation and treatment with ethephon, whereas activities of two moderately anionic peroxidases were markedly increased in TMV-inoculated leaves only. Inoculation with TMV induced systemically two major bands with β-1,3-glucanase activity corresponding to PR-N and PR-O and one minor band of an unknown β-1,3-glucanase. PR-2 had low β-1,3-glucanase activity. Ethephon did not significantly increase systemic β-1,3-glucanase activity. Induced resistance against blue mold and TMV are different and the responses induced by ethephon are insufficient for resistance to blue mold. One difference observed is that TMV induces β-1,3-glucanase activity, whereas ethephon does not. Clearly, chitinase and β-1,3-glucanase activity are not consistently coordinately regulated in tobacco.