PURIFICATION AND CHARACTERIZATION OF COR85-OLIGOMERIC COMPLEX FROM COLD-ACCLIMATED SPINACH

Expression of a cold-regulated protein with a molecular mass of 85 kDa (COR85) is closely associated with the development of freezing tolerance during cold-acclimation of spinach [Kazuoka and Oeda (1992) Plant Cell Physiol. 33: 1107]. In the present study, COR85 was purified from the leaves of cold-acclimated spinach by ion-exchange chromatography. COR85 was a member of the Group II LEA protein family and appeared to form a homo-oligomeric complex with a molecular mass of 350 kDa in the cytosol. Anti-COR85 antiserum cross-reacted with both CORs140 and 85 in spinach, and with some heat-stable CORs from wheat and Arabidopsis. COR85 is inducible in the whole plant by drought and salt stress, but not in roots at low temperature. In the non-stressed plants, COR85 accumulates specifically in the cotyledons and roots at the early stages of development after germination and in the leaves that have become etiolated as a result of natural senescence. We also obtained evidence that COR85 is involved in cryoprotection of freezing-sensitive enzymes. In an assay in vitro, among the nine proteins with a variety of hydrophilicities, COR85 was the most effective in protecting lactate dehydrogenase against denaturation by freezing. Putative functions of COR85 in the dehydrating cells during extracellular freezing are discussed.