Localization, conjugation, and function of salicylic acid in tobacco during the hypersensitive reaction to tobacco mosaic virus

Alexander J. Enyedi, Nasser Yalpani, Paul Silverman, Ilya Raskin

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351 Scopus citations


Salicylic acid (SA) is hypothesized to be a natural signal that triggers the systemic induction of pathogenesis-related proteins and disease resistance in tobacco. When Xanthi-nc (NN genotype) tobacco was inoculated with tobacco mosaic virus (TMV) there was an increase in endogenous SA in both inoculated and virus-free leaves. The highest levels of SA were detected in and around necrotic lesions that formed in response to TMV. Chemical and enzymatic hydrolysis of extracts from TMV-inoculated leaves demonstrated the presence of a SA conjugate tentatively identified as O-β-D-glucosyl-SA. The SA conjugate was detected only in leaves that contained necrotic lesions and was not detected in phloem exudates or uninoculated leaves of TMV-inoculated Xanthi-nc tobacco. When exogenous SA was fed to excised tobacco leaves, it was metabolized within 10 hr. However, this reduction in free SA did not prevent the subsequent accumulation of the PR-1 family of pathogenesis-related proteins. The absence of SA accumulation in TMV-inoculated tobacco plants incubated at 32°C was not a result of the glucosylation of SA. The addition of SA to the medium elevated levels of SA in the leaves of virus-free tobacco grown hydroponically. Increasing the endogenous level of SA in leaves to those naturally observed during systemic acquired resistance resulted in increased resistance to TMV, expressed as a reduction in lesion area. These data further support the hypothesis that SA is a likely natural inducer of pathogenesis-related proteins and systemic acquired resistance in TMV-inoculated Xanthi-nc tobacco.

Original languageEnglish (US)
Pages (from-to)2480-2484
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number6
StatePublished - 1992

All Science Journal Classification (ASJC) codes

  • General


  • Glucosyltransferase
  • Pathogenesis-related proteins
  • Signal transduction
  • Systemic acquired resistance

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