Localization, conjugation, and function of salicylic acid in tobacco during the hypersensitive reaction to tobacco mosaic virus.
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-beta-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 degrees 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.
Enyedi
A J
AJ
Center for Agricultural Molecular Biology, Rutgers, State University of New Jersey, Cook College, New Brunswick 08903-0231.
Yalpani
N
N
Silverman
P
P
Raskin
I
I
D005960:Glucosides / Q000032:analysis; D006868:Hydrolysis; D010940:Plant Proteins / Q000378:metabolism; D010947:Plants, Toxic; D012459:Salicylates / Q000378:metabolism*; D020156:Salicylic Acid; D014026:Nicotiana / Q000382:microbiology / Q000502:physiology*; D014027:Tobacco Mosaic Virus / Q000502:physiology*; D001617:beta-Glucosidase / Q000378:metabolism
D005960:Glucosides; D010940:Plant Proteins; D012459:Salicylates; C053376:pathogenesis-related proteins, plant; D001617:beta-Glucosidase; D020156:Salicylic Acid