Protective Effect of Homologues of Host‐Specific AF‐Toxin I Produced by Alternaria alternata Strawberry Pathotype on Strawberry Cells

Abstract The protective effect of homologues of host‐specific AF‐toxin I from Alternaria alternata strawberry pathotype on susceptible strawberry cells was quantitatively examined by using the cultured cells. Among three AF‐toxin molecules, AF‐toxin II did not exhibit toxicity to strawberry cells, although AF‐toxin I and III were highly toxic to the cells. AF‐toxin II protected strawberry cells from AF‐toxin I action. The protection was remarkable when the cultured cells were exposed to excess amounts of AF‐toxin II both prior to and simultaneously with AF‐toxin I addition. The simultaneous treatment, however, was most effective at preventing AF‐toxin I action: it gave complete protection at a 50 : 1 (toxin II : toxin I) ratio on a molar basis. The epoxy‐decatrienoic acid moiety of the AF‐toxins also prevented the cell death caused by AF‐toxin I, but was less effective than AF‐toxin II. Protection was apparent when the cultured cells were exposed to AF‐toxin II for 3 h, rinsed to remove free AF‐toxin II and then exposed to AF‐toxin I. These results suggest that the toxoids of AF‐toxin I, such as AF‐toxin II and the decatrienoic acid, act as competitive inhibitors of AF‐toxin I.