VIEW ARTICLE

Physiology and Biochemistry

Endogenous Salicylic Acid Levels Correlate with Accumulation of Pathogenesis-Related Proteins and Virus Resistance in Tobacco. N. Yalpani, AgBiotech Center, Cook College, Rutgers University, P.O. Box 231, New Brunswick, NJ 08903-0231; V. Shulaev, and I. Raskin. AgBiotech Center, Cook College, Rutgers University, P.O. Box 231, New Brunswick, NJ 08903-0231. Phytopathology 83:702-708. Accepted for publication 17 February 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-702.

Salicylic acid (SA) is hypothesized to be an endogenous regulator of local and systemic disease resistance and an inducer of pathogenesis-related (PR) proteins among plants. High levels of PR proteins have been observed in an uninoculated amphidiploid hybrid of Nicotiana glutinosa × N. debneyi, which is highly resistant to tobacco mosaic virus (TMV). Fluorescence, UV, and mass spectral analysis established that the levels of SA in healthy N. glutinosa × N. debneyi leaves were 30 times greater than in N. tabacum ‘Xanthi-nc’ tobacco, which does not constitutively express PR proteins and is less resistant to TMV. Upon TMV-inoculation, SA levels increased at least 70-fold in leaves of Xanthi-nc but rose only slightly in the hybrid. Phloem exudates of N. glutinosa × N. debneyi contained at least 500 times more SA than those of Xanthi-nc. SA treatment caused the appearance of PR-1 protein in Xanthi-nc but did not affect constitutively high levels of PR-1 protein in N. glutinosa × N. debneyi. In contrast to Xanthi-nc tobacco, TMV-inoculated N. glutinosa × N. debneyi kept at 32 C accumulated more than 0.5 μg SA/g fresh weight, maintained high levels of PR proteins, and developed a hypersensitive response to TMV. PR proteins have previously been shown to accumulate in the lower leaves of healthy, flowering Xanthi-nc tobacco, which exhibited increased resistance to TMV. These developmentally induced increases in resistance and PR-1 proteins positively correlated with tissue levels of SA. These results affirm the regulatory role of SA in disease resistance and PR protein production.