Abstract
Effect of AL-toxin produced by Alternaria alternata tomato pathotype on viability of cultured cells derived from susceptible and resistant cultivars of tomato was examined. When calli of each cultivar were incubated on solid medium containing the toxin, cell browning occurred only on calli of susceptible cultivar within 3 days after the treatment. For quantitatively estimating the viability of toxin-treated cells, a colorimetric assay utilizing a tetrazolium salt, 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT), was employed. The number of living cells was proportional to the amount of formazan formed by reduction of MTT in active mitochondria, indicating that MTT-colorimetric assay should be useful for the quantitative determination of cell damage induced by the toxin. Formazan production in suspensioncultured cells of susceptible cultivar was inhibited by the toxin at about the same concentration as the minimum concentration for necrosis induction on leaves. In contrast, resistant cells were not affected significantly by the toxin even at higher concentrations. The MTT assay appeared to have some advantages over conventional techniques for evaluating the effect of toxin on cultured cells. Additionally, these results indicate that the host-selective toxicity of AL-toxin is expressed to the cultured cells as well as the plant tissues.
