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Physiology and Biochemistry

Effects of Helminthosporium maydis T-toxin on the Uptake of Uranyl Salts in Corn Roots. Harry Wheeler, Department of Plant Pathology, University of Kentucky, Lexington KY 40506; Vernon D. Ammon, Department of Plant Pathology, University of Kentucky, Lexington KY 40506, Present address junior author: Department of Plant Pathology and Weed Science, Mississippi State University, Mississippi State, MS 39762. Phytopathology 67:325-330. Accepted for publication 31 August 1976. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-325.

Bioassays of Helminthosporium maydis T-toxin based on root growth inhibition, electrolyte loss, and inhibition of transpiration were compared. With four corn inbred lines, those carrying Texas male sterile (Tms) cytoplasm could be separated readily from those with normal (N) cytoplasm by each of these bioassays. The root growth test, however, was more sensitive by at least one order of magnitude than the other two. More than 50 chemical and physical agents were screened but, other than HmT-toxin, none had clear-cut selective effects on Tms inbred lines. As a post-treatment, HmT-toxin at a concentration which inhibited root growth by 90% did not remove uranyl crystals bound to cell walls or release uranyl sequestered in vacuoles of corn root cells. Pretreatment with HmT-toxin did not interfere with binding of uranyl to cell walls but did prevent uranyl uptake into vacuoles and this effect was selective for Tms roots. Inhibition of uptake of uranyl into vacuoles was detectable in Tms roots exposed to HmT-toxin for 30 min and the process was completely blocked in thos pretreated with toxin for 1 hr. In contrast, exposures of 2 hr to the same concentration of HmT-toxin were required to induce significant increases in electrolyte loss. These results support previous suggestions that HmT-toxin alters cell permeability through effects on a specific component of the transport system rather than by general disruption of membranes.

Additional keywords: southern corn leaf blight, pathotoxin, ultrastructure.