Catalysis of the reaction: a 1-acyl-2-hexadecanoyl-glycerolipid + 2 H+ + O2 + 2 reduced - = a 1-acyl-2--glycerolipid + 2 H2O + 2 oxidized -.
1-18:2-2-16:0-monogalactosyldiacylglycerol desaturase activity (SN2-16:1 forming)