Prevents cell division in root meristems and promotes salicylic acid (SA) production and hypersensitive response (HR) (PubMed:26276842). Catalyzes the biosynthesis of ceramide sphingolipids with C(16) fatty acids, structural membrane lipids involved in membrane trafficking (e.g. early endosomes) and cell polarity (e.g. polar auxin transport related proteins); accepts only C16:0 fatty acids, but with a wide range of d18 sphingoid bases, such as sphinganine (d18:0) and palmitoyl-CoA (PubMed:21883234, PubMed:26635357, PubMed:21666002, PubMed:26276842). Mediates resistance to sphinganine-analog mycotoxins (SAMs, e.g. fumonisin B(1)) by restoring the sphingolipid biosynthesis (PubMed:26276842). Could salvage the transport of GPI-anchored proteins from the endoplasmic reticulum to the Golgi apparatus in ceramides-depleted cells after SAM exposure (By similarity). Contributes to hypoxic conditions tolerance (e.g. submergences), especially in the dark, by promoting the formation of very-long-chain (VLC) ceramide species (22:1, 24:1 and 26:1) and of VLC unsaturated ceramides, which are modulating CTR1-mediated ethylene signaling leading to endoplasmic reticulum (ER)-to-nucleus translocation of EIN2 and EIN3 (PubMed:25822663). a sphingoid base + hexadecanoyl-CoA = an N-hexadecanoyl-sphingoid base + CoA + H(+) hexadecanoyl-CoA + sphinganine = CoA + H(+) + N-hexadecanoylsphinganine hexadecanoyl-CoA + sphing-4-enine = CoA + H(+) + N-hexadecanoylsphing-4-enine hexadecanoyl-CoA + sphinga-(4E,8E)-dienine = CoA + H(+) + N-hexadecanoylsphinga-(4E,8E)-dienine hexadecanoyl-CoA + sphinga-(4E,8Z)-dienine = CoA + H(+) + N-hexadecanoylsphinga-(4E,8Z)-dienine Inhibited by the mycotoxin fumonisin B(1), a sphingosine analog mycotoxins produced by pathogenic fungi (PubMed:26276842, PubMed:26635357). Activated by divalent cation such as magnesium Mg(2+), zinc Zn(2+), manganese Mn(2+) and calcium Ca(2+) (PubMed:26635357). Sphingolipid metabolism. Expressed ubiquitously with highest levels in pollen. Elevated levels of free trihydroxy sphingoid bases as well as ceramide and glucosylceramide species with C(20) to C(28) fatty acid, but reduced levels of species with C(16) fatty acids (PubMed:21883234, PubMed:25822663). Better resistance to submergence under light conditions, but increased sensitivity to dark submergence associated with declined levels of unsaturated very-long-chain (VLC) ceramide species (22:1, 24:1 and 26:1) (PubMed:25822663). Increased susceptibility to AAL-toxin triggering programmed cell death (PCD) (PubMed:18725200, PubMed:23617414).