FUMONISIN-INDUCED AND AAL-TOXIN-INDUCED DISRUPTION OF SPHINGOLIPID METABOLISM WITH ACCUMULATION OF FREE SPHINGOID BASES

Fumonisins (FB) and AAL-toxin are sphingoid-like compounds produced by several species of fungi associated with plant diseases. In animal ce lls, both fumonisins produced by Fusarium moniliforme and AAL-toxin pr oduced by Alternaria alternate f. sp. lycopersici inhibit ceramide syn thesis, an early biochemical event in the animal diseases associated w ith consumption of F. moniliforme-contaminated corn. In duckweed (Lemn a pausicostata Heglem. 6746), tomato plants (Lycopersicon esculentum M ill), and tobacco callus (Nicotiana tabacum cv Wisconsin), pure FB1 or AAL-toxin caused a marked elevation of phytosphingosine and sphingani ne, sphingoid bases normally present in low concentrations. The relati ve increases were quite different in the three plant systems. Nonethel ess, disruption of sphingolipid metabolism was clearly a common featur e in plants exposed to FB1 or AAL-toxin. Resistant varieties of tomato (Asc/Asc) were much less sensitive to toxin-induced increases in free sphinganine. Because free sphingoid bases are precursors to plant ''c eramides,'' their accumulation suggests that the primary biochemical l esion is inhibition of de novo ceramide synthesis and reacylation of f ree sphingoid bases. Thus, in plants the disease symptoms associated w ith A. alternate and F. moniliforme infection may be due to disruption of sphingolipid metabolism.