Sesquiterpene synthase involved in the biosynthesis of delta-guaiene (53.7%) and alpha-guaiene (44.6%), two structures composed of five- and seven-membered rings. Produces also 1.7% of alpha-humulene. (2E,6E)-farnesyl diphosphate = delta-guaiene + diphosphate (2E,6E)-farnesyl diphosphate = alpha-guaiene + diphosphate Binds 3 Mg(2+) ions per subunit. kcat is 9.72 x 10(-5) sec(-1) for farnesyl diphosphate. Secondary metabolite biosynthesis; terpenoid biosynthesis. Up-regulated by methyl jasmonate. The Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motif is important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the terpene synthase family.