Heat-Stable COR (<underline>Co</underline>ld-<underline>R</underline>egulated) Proteins Associated with Freezing Tolerance in Spinach

Abstract

While most soluble proteins are coagulated by heating at 100°C for 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 and their mRNAs during cold acclimation of spinach (Spinacia oleracea L.). We analyzed heat-stable proteins and the heat-stable translation products from poly(A)+RNA generated in a wheat germ system. Heat-stable COR proteins with molecular masses of 140 kDa and 85 kDa (CORs 140 and 85), were detected in the leaves of cold-acclimated plants. Increased levels of CORs 140 and 85 correlated with the development of freezing tolerance during cold acclimation. Interestingly, CORs 140 and 85 accumulated specifically in the leaves and stems and not in the roots of the cold-acclimated plants. Consistent with this observation, freezing tolerance was also induced in leaves and stems, but not in roots. These data strongly suggest that CORs 140 and 85 are closely associated with freezing tolerance. Accumulation of COR 85 was also induced by exogenous ABA, drought, and wounding. The possible roles of CORs 140 and 85 in plants acclimating to low temperature is given attention.