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Effects of Toxin from Helminthosporium sacchari on Nongreen Tissues and a Reexamination of Toxin Binding. Mark S. Lesney, Research associate, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824; Robert S. Livingston(2), and Robert P. Scheffer(3). (2)(3)Research assistant, and professor, respectively, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. Phytopathology 72:844-849. Accepted for publication 24 November 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-844.

Green leaves, etiolated shoots, and roots from susceptible clones of sugarcane were sensitive to toxin from Helminthosporium sacchari; comparable tissues of resistant clones were not affected. Indications from previous work were that the toxin first affects chloroplasts, and that chloroplasts may be required for other effects. Our results indicate toxic effects on green and nongreen tissues and no requirement for functional chloroplasts. Next, using the established methods, we repeated earlier work on toxin binding. Equilibrium dialysis of 14C-toxin against membrane preparations gave no indication of toxin binding to preparations from either resistant or susceptible tissues. Also, there was no indication of toxin binding to high-molecular-weight materials from membrane preparations of susceptible and resistant clones incubated with 14C-toxin and then fractionated on gel columns. Thus, the mode of toxic action remains an open question. When proper precautions were not taken, quenching of counts and chemiluminescence proved to be problems with preparations of this type. Binding may be involved in toxic action, but a toxin preparation with a more active label than any used to date may be required to prove it.