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

Abstract

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-fi-Dglucosyl-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 32C 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.

Differential Activity of Peroxidase Isozymes in Response to Wounding, Gypsy Moth, and Plant Hormones in Northern Red Oak (Quercus rubra L.)

“…Isoform A3.9 activity was enhanced by treatment with SA (P = 0.055), a signal more associated with plant defense responses to microbes (Enyedi et al, 1992;Choi et al, 1994;Conti et al, 1996). It is possible, although unlikely, that our trees were incidentally infected by microbes during that particular treatment despite sterilizing the leaf punch, and that A3.9 is both wound-and microberesponsive.…”

Salicylic Acid Produced by the Rhizobacterium Pseudomonas aeruginosa 7NSK2 Induces Resistance to Leaf Infection by Botrytis cinerea on Bean

“…SA is considered to mediate plant responses to pathogens (5) and is associated with pathogen-induced SAR (4). In most cases, SA application to plants has only a local effect on pathogens, but in tobacco, radish, and Arabidopsis, a systemic resistance to pathogens has been observed after root or soil treatment with SA (7,18,27,35). In hydroponically grown radish plants, a range of SA concentrations from 100 µg to 100 fg root -1 was able to induce ISR to Fusarium wilt, suggesting that there is no dose effect for SA (18).…”

“…Salicylic acid (SA) is another siderophore produced by P. fluorescens WCS374, WCS417r (18), and CHA0 (24) that could be involved in ISR. SA is important in pathogen-induced SAR (4) and can induce a systemic resistance to pathogens after root or soil treatment (7,18,24,35). Up to now, evidence for the involvement of bacterial SA in ISR is still circumstantial (18), because no SAdeficient mutants of ISR-inducing rhizobacteria have been tested on ISR induction.…”

The hypersensitive response and the induction of cell death in plants

“…The recent finding that the lls1 mutant from maize encodes a probable dioxygenase (Gray et al, 1997) raises the possibility that this gene is involved in detoxification of oxidized phenolic compounds such as salicyclic acid (SA). SA can promote cell death (Naton et al, 1996;Shirasu et al, 1997) and considerable levels of SA accumulate during the HR (Eneydi et al, 1992). Therefore Lls1 could act as a suppressor of cell death by scavenging SA or a related phenolic compound.…”