Submitted to: Toxicological Sciences
Publication Type: Abstract Only
Publication Acceptance Date: 11/1/2005
Publication Date: 3/1/2006
Citation: Williams, L.D., Glenn, A.E., Bacon, C.W., Smith, M.A., Riley, R.T. 2006. Evidence for increased sphingoid base 1-phosphate lyase activity in corn seedlings after prolonged exposure to fumonisin [abstract]. Toxicological Sciences 90(1):408. Interpretive Summary: Abstract - no summary.
Technical Abstract: The fungus Fusarium verticillioides infects corn and produces mycotoxins known as fumonisins, with fumonisin B1 (FB1) being the most prevalent. FB1 inhibits the enzyme ceramide synthase, which causes an increase in free sphinganine (Sa) and phytosphingosine (Pso) as well as their 1-phosphate metabolites in plants. Our previous studies have indicated that FB1 can accumulate in soils, can move through soils intact and can be bound to soils. To determine the role of fumonisins in F. verticillioides corn seedling disease and on sphingolipid biosynthesis, corn seeds were inoculated with pathogenic or non-pathogenic strains of F. verticillioides. Only the seedlings grown from seed inoculated with the pathogenic strain showed signs of pathology. After harvest, the roots were analyzed for Sa, Pso, Sa-1-P, Pso-1-P and fumonisin; and the soils were also analyzed for fumonisin. Only seedlings inoculated with the pathogenic strain of F. verticillioides had detectable fumonisins in the roots and elevated levels of Sa, Pso, Sa-1-P and Pso-1-P in the roots. In subsequent studies, un-inoculated corn seed were watered with FB1. The seedlings were harvested 8 or 21 days after planting. There was a dose dependent elevation in Sa, Pso, Sa-1-P and Pso-1-P in the roots at both time points. The accumulation of sphingoid base 1-phosphates in roots suggests that the activity of serine palmitoyl transferase and sphingoid base kinase exceed the ability of sphingoid base 1-phosphate lyase to degrade the sphingoid base 1 phosphates. However, on day 21 both Sa-1-P and Pso-1-P were both reduced by approximately 50% to 75% at every dose level compared to their levels on day 8, while Sa and Pso were not. The reduction in accumulated sphingoid base 1-phosphates on day 21 could indicate that the sphingoid base 1-phosphate lyases are induced after prolonged exposure and that this results in more efficient degradation of the products of the sphingoid base.