Biochemical and Serological Studies of Pathogenesis-related Proteins of Nicotiana Species

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Abstract
Summary Pathogenesis-related proteins (PR proteins), found in leaves of different Nicotiana spp. infected with tobacco mosaic virus (TMV) or treated with potassium salicylate, were compared biochemically and also serologically using an antibody to PR1a purified from TMV-infected leaves of Nicotiana tabacum cv. Samsun NN. The antibody preparation reacted with PR proteins, PR1a, PR1b and PR1c, from four cultivars of N. tabacum and with a PR protein, b1″, from TMV-infected leaves of Nicotiana glutinosa, but not with a PR protein, PR2, from cv. Samsun NN. The isoelectric points in 9 m-urea of PR1a and PR1b from N. tabacum cv. Samsun NN were pH 4.3 and 4.8, respectively. Partial proteolysis of PR1a and PR1b with Pronase E yielded peptides which, although similar in size to those from PR1b, differed from them serologically. When Staphylococcus aureus V8 protease was used, the peptides released from each protein differed both in size and serological reaction. The patterns of peptides released from b1″ of N. glutinosa by V8 protease and Pronase E were different from those of peptides from PR1a and PR1b from N. tabacum. The antibody preparation reacted strongly with one of four peptides released by Pronase E and with two of the three peptides released by V8 protease. These results indicate that PR1a, PR1b and PR1c from N. tabacum and b1″ from N. glutinosa contain some similar antigenic determinants and have similar structures, and confirm that PR1a and PR1b are very similar but not identical in their primary structures.