Effect of the Specific Toxin in Helminthosporium victoriae on Host Cell Membranes

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Abstract
H. victoriae toxin, which affects only hosts of the toxin-producing fungus, causes loss of electrolytes from roots, leaves, and coleoptiles of treated plants. Root hair cells lost the ability to plasmolyze after 20 min. exposure to toxin in solution; comparable resistant cells retained plasmolytic ability during 3 hr. exposure. Toxin stopped uptake of exogenous amino acids and Pi by susceptible but not by resistant tissue. Incorporation of 32p into organic-P and 14C-amino acids into protein was blocked in susceptible but not in resistant tissue. Apparent free space increased in susceptible but not in resistant roots. The increase was evident within 30 min. and reached 80% free space after 2 hr. exposure to toxin. When cell wall-free protoplasts were exposed to 0.16 [mu]g toxin/ml, protoplasmic streaming stopped and all plasma membranes of susceptible protoplasts broke within 1 hr. Resistant protoplasts were not affected significantly. Data support the hypothesis of a primary lesion of toxin in the plasma membrane. Effects on synthesis could result from lack of transport of exogenous solutes to sites of synthesis. It is possible that all other observed effects of toxin are secondary to membrane damage.