Converts stearoyl-ACP to oleoyl-ACP by introduction of a cis double bond between carbons Delta(9) and Delta(10) of the acyl chain. 2 H(+) + O2 + octadecanoyl-[ACP] + 2 reduced [2Fe-2S]-[ferredoxin] = (9Z)-octadecenoyl-[ACP] + 2 H2O + 2 oxidized [2Fe-2S]-[ferredoxin] Binds 2 Fe(2+) ions per subunit. Lipid metabolism; fatty acid metabolism. Homodimer. Developing seeds. Induced by 25 days after anthesis (dAA), peaking at 45 dAA but decreasing considerably thereafter. Belongs to the fatty acid desaturase type 2 family.