Involved in delta-9 desaturation of fatty acids (Probable) (PubMed:17156034, PubMed:15240892). Involved in the production of very-long-chain fatty acids (VLCFAs) (PubMed:23175755). May desaturate chloroplastic monogalactosyl diacylglycerol (MGDG) and alter chloroplast membrane fluidity, which is required to prime a cold acclimation response (PubMed:27062193). Lipid metabolism; polyunsaturated fatty acid biosynthesis. Strongly expressed in inflorescence meristems, leaves, and flowers, and weakly in roots and seedpods. Down-regulated by cold. The histidine box domains may contain the active site and/or be involved in metal ion binding. No visible phenotype under normal growth conditions, but mutant plants display enhanced freezing tolerance upon cold acclimation. Substrate specificity shifts from delta-9 to delta-7 desaturation when the protein is retargeted to the chloroplast. Belongs to the fatty acid desaturase type 1 family.