Effects of the Host-Selective Toxins ofAlternaria alternataf. sp.lycopersicion Suspension-Cultured Tomato Cells

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Abstract
Tomato cell cultures were used to investigate the metabolic effects of the host-selective toxins produced by Alternaria alternata f. sp. lycopersici, a pathogen of tomato. Toxin concentrations of approximately 1 .mu.M were sufficient to strongly inhibit cell expansion [Lycopersicon esculentum, L. peruvianum], accumulation of dry matter, and cell division in suspension cultures. Growth-inhibitory concentrations of toxin did not inhibit respiration, uptake of [3H] leucine or its incorporation into protein, or uptake of [3-14C] pyruvate or its incorporation into lipids. The toxins also did not induce potassium ion leakage. The toxins did inhibit uptake of [3H]uridine and [3H]thymidine but apparently did not inhibit net synthesis of RNA or DNA; the inhibition of uridine and thymidine uptake probably was not the cause of growth inhibition. The toxins apparently did not induce pyrimidine shortage, because toxin sensitivity was unaffected by supplementing cultures with pyrimidines or aspartate. Our results in cultured cells do not support the theory that these toxins inhibit aspartate carbamoyltransferase, an enzyme involved in pyrimidine biosynthesis.