Heat-Stable COR (Cold-Regulated) Proteins Associated with Freezing Tolerance in Spinach

While most soluble proteins are coagulated by heating at 100°Cfor 10 minutes, some highly hydrophilic COR (Cold-regulated)proteins remain soluble in aqueous solution (Lin et al. 1990).We report here changes in levels of heat-stable proteins andtheir mRNAs during cold acclimation of spinach (Spinacia oleraceaL.). We analyzed heat-stable proteins and the heat-stable translationproducts from poly(A)⁺RNA generated in a wheat germ system.Heat-stable COR proteins with molecular masses of 140 kDa and85 kDa (CORs 140 and 85), were detected in the leaves of cold-acclimatedplants. Increased levels of CORs 140 and 85 correlated withthe development of freezing tolerance during cold acclimation.Interestingly, CORs 140 and 85 accumulated specifically in theleaves and stems and not in the roots of the cold-acclimatedplants. Consistent with this observation, freezing tolerancewas also induced in leaves and stems, but not in roots. Thesedata strongly suggest that CORs 140 and 85 are closely associatedwith freezing tolerance. Accumulation of COR 85 was also inducedby exogenous ABA, drought, and wounding. The possible rolesof CORs 140 and 85 in plants acclimating to low temperatureis given attention. (Received June 11, 1992; Accepted September 1, 1992)