Potato virus YNTN causes necrotic lesions in leaves of susceptible plants and plants reacting to infection with a hypersensitive response. In this study, we used different histological techniques to analyse the lesions at the tissue and cell level, measured their size, localised the occurrence of programmed cell death and the accumulation of phenolic acids and flavonoids in leaves of genetically different potato plants (Solanum tuberosum L.) cv. Rywal and NahG-Rywal. Lesion diameter measurements on leaf cross-sections showed that NahG-Rywal plants develop significantly larger lesions than cv. Rywal plants. Additional measurements of the lesion area on fresh leaf preparations showed a slight difference between the two genotypes, but this was not statistically significant. Using TUNEL reaction we detected fragmented DNA in the nuclei of necrotic cells and in the vicinity of the lesion in leaves of NahG-Rywal plants, which could be the result of programmed cell death. The presence of phenolic compounds, such as ferulic acid, in the lesion area was detected by autofluorescence changes in alkaline medium. The presence of flavonoids was confirmed in the cells around the lesions in fresh preparations of infected leaves, whereas their staining on fixed tissue was unsuccessful.
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