Increased allergen production in turnip (Brassica rapa) by treatments activating defense mechanisms

Background: Practical applications to enhance the productivity of agricultu re by using plants with improved resistance to pathogens are expected to in crease in the near future. Defense proteins play an important role in patho gen resistance, and some defense-related proteins are significant cross-rea cting allergens. For example, cross-allergies are common among patients all ergic to natural rubber latex (NRL), which contains many defense-related pr oteins. Objective: Using a model plant (ie, turnip), we studied whether allergen co ntents increase after treatments activating defense mechanisms of the plant s. Methods: Whole or wounded turnips treated with salicylic acid, ethephon, or water mere incubated for 2, 4, or 8 days, Allergen content was investigate d by IgE immunoblotting with sera from patients allergic to NRL, An induced protein that bound IgE most intensively was purified and Further character ized by mass analysis, amino acid sequencing, IgE-ELISA, and skin prick tes ts. Results: In immunoblotting, clear IgE-binding bands were discernible only i n samples from chemically treated plants. IgE was bound most intensively to a protein with an apparent molecular weight of 25 kd in SDS-PAGE and with a determined molecular weight of 18.7 kd, Sequenced peptides of the 18.7-kd protein showed over 70% homology to prohevein, a major allergen of NRL, an d to many other prohevein-like defense proteins. In ELISA, sera from 30 of 34 (88%) adults and 21 of 26 (81%) children previously shown to have IgE ag ainst prohevein bound to the purified protein. In skin prick testing with t he protein, 4 of 6 patients allergic to NRL had positive reactions, Conclusion: These results demonstrate that activating defense mechanisms of plants may considerably increase their allergen content.