Biochemical and serological characterization of b-proteins fromNicotiana species

Proteins associated with the hypersensitive response (b-proteins) were purified from variousNicotiana species and compared biochemically and serologically. The method developed to purify proteins b1, b2 and b3 ofN. tabacum cv. Xanthi-nc was used to purify b-proteins present inN. sylvestris (b0, b1 and b3) andN. tomentosiformis (b2), the parental species ofN. tabacum, and b1″ from bothN. glutinosa andN. debneyi. Ultracentrifugation and amino acid analysis of some of these proteins has shown that they are very similar and that they are all monomers in their native form (mol wt = 15 700 for b0, b1, b2 and b3; mol wt = 13 800 for b1″).Based on their reactions to an antiserum produced against protein b1 ofN. tabacum cv. Xanthi-nc, 3 serological groups can be recognized which are independent of the source species (I) b0 and b1, (II) b1″ and b2, (III) b3. Thus, proteins in the same serological group but from different species are more closely related than the b-proteins in different serological groups but present in the same species. The implication of this site on the possible phylogeny of b-proteins is discussed.Serological tests confirmed the b-protein present as a constitutive component in the virus resistant interspecific hybrids ofN. glutinosa ×N. debneyi as protein b1″.