Exhibits cryoprotective activity toward stromal substrates (e.g. LDH and rubisco) in chloroplasts and in protoplasts and confers freezing tolerance to plants in a CBF-dependent manner (PubMed:1567390, PubMed:11038526, PubMed:9826741, PubMed:17384167, PubMed:18540080, PubMed:19563440). Protectant against various stresses (e.g. cold, drought and heat stress) by preventing protein aggregation (e.g. LDH) and attenuating enzyme inactivation (PubMed:18540080). Influences the intrinsic curvature of the inner membrane of the chloroplast envelope, and modulates the freeze-induced lamellar-to-hexagonal II phase transitions that occur in regions where the plasma membrane is brought into close apposition with the chloroplast envelope during freeze-induced osmotic contraction (PubMed:9826741). Mediates a shift in the melting curves of phospholipids-containing membranes to lower temperatures (PubMed:20510170). Involved in the regulation of leaf senescence by abscisic acid (ABA) in a VNI2-dependent manner (PubMed:21673078). Forms homooligomers which interact with potential stromal substrates in the stroma of chloroplasts (PubMed:17384167). Interacts with the galactose headgroup of the chloroplast lipid monogalactosyldiacylglycerol (MGDG) (PubMed:20510170). Additional isoforms seem to exist. Accumulates in leaves during cold acclimation (at protein level) (PubMed:16668917, PubMed:17384167). Strongly induced by cold in association with a gradual irreversible decrease of H3K27me3 in the promoter region (PubMed:8193295, PubMed:9668134, PubMed:11706173, PubMed:11779861, PubMed:12148528, PubMed:14745450, PubMed:15144380, PubMed:16258011, PubMed:19470100, PubMed:19500304, PubMed:19563440). Expressed transiently after moderate decrease in temperature (cooling) through the CBF signaling cascade, thus leading to an enhanced subsequent freezing resistance (PubMed:19563440). Accumulates in response to high light, drought, high salt, polyethylene glycol (PEG) and abscisic acid (ABA) (PubMed:8193295, PubMed:9668134, PubMed:11779861, PubMed:12148528, PubMed:12785063, PubMed:21673078, PubMed:21832142). Cold-mediated induction is light-dependent and light-stimulated, and requires functional chloroplasts (PubMed:12148528, PubMed:17384167, PubMed:21471455). Follow a circadian-regulated expression with a progressive accumulation during the light phase and a drop during the dark phase (PubMed:21471455). Remaining soluble upon boiling in aqueous solution. Oligomers can stay soluble with small structural change after boiling and freeze-thaw treatments (PubMed:16668917, PubMed:17384167). Predominantly unstructured in solution and mainly alpha-helical after drying (PubMed:20510170). Belongs to the COR15 protein family.