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Influence of Helminthosporium maydis, Race T, Toxin on Potassium Uptake in Maize Roots ^1,2

Department of Agronomy, Purdue University, West Lafayette, Indiana 47907, Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907

The effect of a toxin extract of Helminthosporium maydis, race T on K⁺ (⁸⁶Rb) uptake by excised root segments of normal (N) and Texas cytoplasmic male-sterile (T) versions of corn inbred W64A was investigated. The uptake of K⁺ was inhibited in both N and T roots by the toxin. This was true for both basal (freshly excised) and augmented (pretreated with aeration) K⁺ uptake. Augmented uptake was more toxin-sensitive than basal uptake (irrespective of cytoplasm type), and the augmented uptake in T roots was seven to eight times more toxin-sensitive than in N roots.

Specific zones of roots differed in their basal and augmented K⁺ uptake rates as well as their toxin sensitivities. The root apex of T was more sensitive to toxin than the apex of N roots when basal K⁺ uptake was measured. In mature zones of the root, T was more sensitive than N when augmented rates were measured. During the development of the augmented K⁺ uptake capacity in either N or T roots, the sensitivity to the toxin did not change; uptake in N roots was inhibited by 10 to 25% and uptake in T roots was inhibited by 70 to 80%.

The difference in toxin sensitivity of K⁺ uptake between N and T roots may be due to N possessing a protective mechanism which is deficient in T.

² This paper is dedicated to Dr. Leon Bernstein—a genuine professional and gentleman.