Catalysis of the reaction: a (9Z,12Z)-octadecadienoyl-containing glycerolipid + 2 Fe(II)- + 2 H+ + O2 = a (5Z,9Z,12Z)-octadecatrienoyl-containing glycerolipid + 2 Fe(III)- + 2 H2O. Can also use a substrate with 3 double bonds (a (9Z,12Z,15Z)-octadecatrienoyl-containing glycerolipid) and add a fourth double bond (a (5Z,9Z,12Z,15Z)-octadecatetraenoyl-containing glycerolipid).
alpha-linolenate delta5 desaturase activity