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Technique for Using Isolated Corn Root Cap Cells in a Simple, Quantitative Assay for the Pathotoxin Produced by Helminthosporium maydis Race T. Martha C. Hawes, Department of Plant Pathology, University of Florida, Gainesville 32611; Phytopathology 73:1184-1187. Accepted for publication 1 April 1983. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-1184.

Root cap cells from corn with Texas male sterile (Tms) cytoplasm were much more sensitive to HMT-toxin, the pathotoxin produced by Helminthosporium maydis race T. than cells from corn with normal (N) cytoplasm. Root cap cells were isolated by gentle agitation of the root in water, and the isolated cells were used to assay HMT-toxin. Each root cap yielded 3- 4 x 10³ cells, which were judged to be 98- 100% viable by staining with fluorescein diacetate. Toxin-induced cell death was highly temperature-dependent. At 35 C, 5 ng HMT-toxin per milliliter began to kill Tms cells within 6- 8 hr and 50 ng/ml or more caused nearly 100% cell death within 10- 12 hr. At least 50 μg/ml was required to kill N-cytoplasm corn root cap cells. The rate of cell death was influenced by cell concentration, but not by plasmolysis. Isolated root cap cells provided a simple, sensitive, quantitative assay for HMT-toxin. The assay was used to compare the lethal effects of HMT-toxin with cell death of oats caused by victorin, the pathotoxin produced by H. victoriae.