ANTIFREEZE PROTEIN ACCUMULATION IN FREEZING-TOLERANT CEREALS

Freezing-tolerant plants withstand extracellular ice formation at subz ero temperatures. Previous studies have shown that winter rye (Secale cereale L.) accumulates proteins in the leaf apoplast during cold accl imation that have antifreeze properties and are similar to pathogenesi s-related proteins. To determine whether the accumulation of these ant ifreeze proteins is common among herbaceous plants, we assayed antifre eze activity and total protein content in leaf apoplastic extracts fro m a number of species grown at low temperature, including both monocot yledons (winter and spring lye, winter and spring wheat, winter barley , spring oats, maize) and dicotyledons (spinach, winter and spring oil seed rape [canola], kale, tobacco). Apoplastic polypeptides were also separated by SDS-PAGE and immunoblotted to determine whether plants ge nerally respond to low temperature by accumulating pathogenesis-relate d proteins. Our results showed that significant levels of antifreeze a ctivity were present only in the apoplast of freezing-tolerant monocot yledons after cold acclimation at 5/2 degrees C. Moreover, only a clos ely related group of plants, rye, wheat and barley, accumulated antifr eeze proteins similar to pathogenesis-related proteins during cold acc limation. The results indicate that the accumulation of antifreeze pro teins is a specific response that may be important in the freezing tol erance of some plants, rather than a general response of all plants to low temperature stress.