Snow-mold-induced apoplastic proteins in winter rye leaves lack antifreezeactivity

During cold acclimation, winter rye (Secale cereale L.) plants secrete anti freeze proteins that are similar to pathogenesis-related (PR) proteins. In this experiment, the secretion of PR proteins was induced at warm temperatu res by infection with pink snow mold (Microdochium nivale), a pathogen of o verwintering cereals. A comparison of cold-induced and pathogen-induced pro teins showed that PR proteins accumulated in the leaf apoplast to a greater level in response to cold. The PR proteins induced by cold and by snow mol d were similar when separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and examined by immunoblotting. Both groups of PR proteins contained glucanase-like, chitinase-like, and thaumatin-like proteins, and both groups exhibited similar levels of glucanase and chitinase activities. However, only the PR proteins induced by cold exhibited antifreeze activit y. Our findings suggest that the cold-induced PR proteins may be isoforms t hat function as antifreeze proteins to modify the growth of ice during free zing while also providing resistance to the growth of low-temperature patho gens in advance of infection. Both functions of the cold-induced PR protein s may improve the survival of overwintering cereals.