2 (2E,6E)-farnesyl diphosphate + H(+) + NADPH = 2 diphosphate + NADP(+) + squalene 2 (2E,6E)-farnesyl diphosphate + H(+) + NADH = 2 diphosphate + NAD(+) + squalene Terpene metabolism; lanosterol biosynthesis; lanosterol from farnesyl diphosphate: step 1/3. Expressed in all tissues analyzed (seedlings, cotyledons, inflorescences, siliques, leaves, stems and roots). Highly expressed in roots and pollen. First observed in very early stages of seedling development. Particularly expressed in the vascular tissues and the petioles. Belongs to the phytoene/squalene synthase family.