Involved in the production of sphingolipid metabolites. Active on sphingosine, phytosphingosine (PHS, 4-hydroxysphinganine), D-erythro-dihydrosphingosine, D-erythro-sphingosine and trans-4, trans-8-sphingadienine, an LCB found exclusively in plants, but not on N-acetyl-dihydrosphingosine (C2-dihydroceramide) and D-threo-dihydrosphingosine. A number of isoforms are produced. According to EST sequences. Expressed in roots, stems, leaves and at higher levels in flowers. Not induced by low-humidity stress or by abscisic acid treatment.