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

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Abstract
Basal K+ uptake in the root midzone region (cm 2 + 3 + 4) of N and T cytoplasmic versions of each of 4 maize inbreds was equally sensitive to the toxin(s) of H. maydis, race T. Basal K+ uptake in the root apex (0-1 cm) and augmented K+ uptake in the root midzone were more toxin-sensitive in inbreds W64A(T) and Mo17(T) than in inbreds W64A(N) and Mo17(N). This differential response of N and T cytoplasms to toxins was not found for corresponding cytoplasms of inbreds WF9 and B37. Development of the augmented K+ uptake rate in midzone segments of W64A(T) was blocked by a toxin concentration which did not affect augmentation development in W64A(N). Augmentation development was more toxin-sensitive in T than in N cytoplasmic versions of all inbreds tested. Fertility-restoring nuclear loci decreased but did not eliminate the toxin sensitivity of augmentation development as observed in root midzones of inbred A619(T). Chloramphenicol- and/or cycloheximide-sensitive protein synthesis was required for augmentation development, but not for expression of either basal or augmented K+ uptake.