The pathogenesis-related proteins of tobacco - their induction by viruses in intact plants and their induction by chemicals in detached leaves

Many of the proteins in extracts of uninfected leaves of Xanthi-nc. tobacco that can be resolved by electrophoresis, are removed or diminished by digestion 'with proteolytic enzymes. At least 10 of the proteins of tobacco mosaic virus-infected leaves, including the 4 recognized pathogenesis-related (PR) proteins are comparatively resistant to digestion. By using this resistance, the two major PR proteins of infected leaves can be semi-quantitatively assayeds and the course of their synthesis followed. They appear in un-inoculated leaves of infected plants about 4 days after their appearance in inoculated leaves, and their accumulation, differs from that of trypsin inhibitors, which virus inoculation also induces.

Detached leaves of uninfected plants, like intact plants, produce PR proteins when treated with acetyl salicylic acid, and with mannitol. They also produce PR proteins when treated with low-molecular weight compounds extracted from both healthy and infected tobacco leaves. These extracts are toxic to leaves, and this synthesis is likely to be a response to stress rather than to a specific “wound-hormone”. The proportions in which the proteins are synthesized however, differ from that in which they are produced by manmtol-mduced stress.