The effects of elevated glutathione levels on defence responses to powdery mildew (Euoidium longipes) were investigated in a salicylic acid‐deficient tobacco (Nicotiana tabacum cv. Xanthi NahG) and wild‐type cv. Xanthi plants, where salicylic acid (SA) contents are normal. Aqueous solutions of reduced glutathione (GSH) and its synthetic precursor R‐2‐oxothiazolidine‐4‐carboxylic acid (OTC) were injected into leaves of tobacco plants 3 h before powdery mildew inoculation. SA‐deficient NahG tobacco was hyper‐susceptible to E. longipes, as judged by significantly more severe powdery mildew symptoms and enhanced pathogen accumulation. Strikingly, elevation of GSH levels in SA‐deficient NahG tobacco restored susceptibility to E. longipes to the extent seen in wild‐type plants (i.e. enhanced basal resistance). However, expression of the SA‐mediated pathogenesis‐related gene (NtPR‐1a) did not increase significantly in GSH or OTC‐pretreated and powdery mildew‐inoculated NahG tobacco, suggesting that the induction of this PR gene may not be directly involved in the defence responses induced by GSH. Our results demonstrate that artificial elevation of glutathione content can significantly reduce susceptibility to powdery mildew in SA‐deficient tobacco.

SummarySurface-enhanced Raman spectra (SERS) of p-dimethylaminobenzylidenerhodanine have been recorded on silica gel 60 F254 and Si60 F254 Raman TLC plates. Spectra were enhanced by use of a silver sol prepared according to the modified Lee-Meisel procedure. The standard deviations of the intensities and the band ratios for the seven most intense peaks were calculated for 30 parallel measurements. Although the Raman plate gives more reproducible results, several experimental difficulties are encountered in the development of chromatograms. SERS detection ofascorbigen and 1 '-methylascorbigen was performed after chromatography on silica gel 60 F254 TLC and HPTLC plates and on Si60 F254 Raman TLC plates. Traditional development was used for the silica gel 60 F254 TLC plates and Si60 F254 Raman plates, and the personal OPLC technique for the silica gel 60 F254 HPTLC plates. It was found that the SERS spectrum gave information about the indole ring only. Because bonding of the analyte to the stationary phase results in a change in molecular conformation-in contrast with the behaviour of rhodanine-the type of the plate used and the development procedure employed can significantly influence the quality of the SERS spectrum.