Influence of Helminthosporium maydis, Race T, Toxin on Potassium Uptake in Maize Roots.

The effect of a toxin extract of Helminthosporium maydis, race T on K(+) ((86)Rb) 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.