The enzyme, characterized from cyanobacteria, introduces a cis double bond at carbon 6 of linoleoyl groups (18:2) attached to the sn-1 position of glycerolipids. The enzyme is a front-end desaturase, introducing the new double bond between a pre-existing double bond and the carboxyl-end of the fatty acid. It is nonspecific with respect to the polar head group of the glycerolipid.