ANTIFREEZE PROTEINS IN WINTER RYE ARE SIMILAR TO PATHOGENESIS-RELATEDPROTEINS

The ability to control extracellular ice formation during freezing is critical to the survival of freezing-tolerant plants. Antifreeze prote ins, which are proteins that have the ability to retard ice crystal gr owth, were recently identified as the most abundant apoplastic protein s in cold-acclimated winter rye (Secale cereale L.) leaves. In the exp eriments reported here, amino-terminal sequence comparisons, immuno-cr oss-reactions, and enzyme activity assays all indicated that these ant ifreeze proteins are similar to members of three classes of pathogenes is-related proteins, namely, endochitinases, endo-beta-1,3-glucanases, and thaumatin-like proteins. Apoplastic endochitinases and endo-beta- 1,3-glucanases that were induced by pathogens in freezing-sensitive to bacco did not exhibit antifreeze activity. Our findings suggest that s ubtle structural differences may have evolved in the pathogenesis-rela ted proteins that accumulate at cold temperatures in winter rye to con fer upon these proteins the ability to bind to ice.