Isolation and characterization of host-selective toxin from Helminthosporium sacchari.

Helminthosporium sacchari infects certain clones of sugar cane and produces a toxin with the same plant selectivity as the fungus itself. The toxin was purified by use of activated charcoal plus thin layer, gel, and ion exchange chromatography. Gas chromatography (GC) of a trimethylsilyl derivative of toxin gave a single peak. Toxin was characterized by GC, mass spectroscopy (MS), and NMR spectroscopy. The spectra of hydrolytic products showed that toxin contains galactose plus a C15H21 moiety which appears to be a sesquiterpene. Spectral data and methylation procedures showed that toxin contains an oligosaccharide composed of beta, 1 leads to 5 galactofuranose units (probably 5 units). Several interconvertible forms of the C15H21 moiety were evident after acid hydrolysis. Toxin was separated from 3 closely related, nontoxic compounds ("noxins"), which contained galactose plus the C15H21 moiety. Comparative data show that the toxin examined in this study is the same as the toxin described by Steiner and Strobel (Steiner, G. W., and Strobel, G. A. (1971) J. Biol. Chem. 246, 4350-4357). The data also show that the previously proposed structure is incorrect.