Fatty acid desaturase involved in the first desaturation step leading to the formation of hexadeca 7,10,13-trienoic acid (16:3(7Z,10Z,13Z)), the major functional components of thylakoid membranes (PubMed:15579662, PubMed:16666902, PubMed:15240892). Required for chloroplast biogenesis at low temperature (PubMed:16668849). Also indirectly involved in the production of the oxylipin dinor-oxo-phyto-dienoic acid implicated in wound signaling (PubMed:15579662). a 1-acyl-2-hexadecanoyl-glycerolipid + 2 H(+) + O2 + 2 reduced [2Fe-2S]-[ferredoxin] = a 1-acyl-2-[(7Z)-hexadecenoyl]-glycerolipid + 2 H2O + 2 oxidized [2Fe-2S]-[ferredoxin] Lipid metabolism; oxylipin biosynthesis. Lipid metabolism; polyunsaturated fatty acid biosynthesis. Highly expressed in young leaves. Low expression in roots. The histidine box domains are involved in binding the catalytic metal ions. Substrate specificity shifts from delta-7 to delta-9 desaturation when the protein is retargeted to the cytoplasm. Belongs to the fatty acid desaturase type 1 family.