Selective Toxins and Analogs Produced by Helminthosporium sacchari

Helminthosporium sacchari toxin and several lower molecular weight, nontoxic analogs were isolated from culture filtrates. Three isomers of the toxin (A, B, and C), each with four galactose units, were separated by high performance liquid chromatography. Isomer C had the highest and isomer A had the lowest toxicity to H. sacchari-susceptible sugarcane; resistant clones were not affected. Each toxin isomer was partially digested with a beta-galactofuranosidase and the resulting analogs (seven from each toxin isomer) were separated by reverse phase high performance liquid chromatography and identified. Each isomer of the analogs with 3 galactose units per mole also was partially digested and the arrangement of galactose units was determined. The compound with one galactose attached to position 2 of the bicyclic sesquiterpene and with 2 galactose units attached to position 13 (analog A(1,2)) was highly toxic to some but not to all clones of H. sacchari-susceptible sugarcane. Toxin analogs protected sensitive tissue against active toxin; protective effects of the analogs differed, but at least a 10-fold excess of analog was required. Analog C(2,1) was more effective at preventing toxin C-induced electrolyte losses than was any other analog. Each of the 3-galactose analog isomers protected better than did any of the 2-galactose compounds. The 1,1 analogs did not protect as well as did the 2,0 or 0,2 analogs. Thus, the sesquiterpene isomer, the number of galactose units, and the galactose arrangement pattern determine the effectiveness of the compound in induction of electrolyte loss and in prevention of toxininduced loss from sugarcane tissues.