Accumulation of pathogenesis-related proteins in tobacco leaves irradiatedwith UV-B

Seedlings of Nicotiana tabacum L, (cv, Petit Havana SR1) were grown under u ltraviolet-B (UV-B, 290-320 nm) irradiation, and soluble proteins were extr acted from the leaves, Two-dimensional electrophoresis revealed that a mini mum of 12 polypeptides were induced by UV-B, Polypeptides which were so abu ndant as to be detectable by Coomassie brilliant blue staining were then su bjected to N-terminal amino acid sequence analyses. Two of the polypeptides were identified as a 23 kDa protein of PS II and 6 as a pathogenesis-relat ed protein 5 (PR-5), Immunoblotting demonstrated that other PR proteins, PR -1 and PR-3 were also induced by UV-B. Salicylic acid (SA), which is an imp ortant component of signal transduction that leads to the expression of PR proteins and exhibition of acquired resistance to pathogens, increased in r esponse to exposure to UV-B. In addition, the activity of phenylalanine amm onialyase, which catalyzes the synthesis from phenylalanine of trans-cinnam ic acid, the endogenous precursor of SA, was transiently increased by UV-B irradiation, These results suggest that UV-B activates the signal transduct ion pathway, which is a common step in pathogen infection.