Characterization of augmented potassium uptake in the seedling primary root of inbred maize (Zea mays)

Abstract

As the seedling primary root of maize inbred W64A elongates, basal and augmented K+(86Rb) uptake rates increase in regions increasingly distant from the apex and in regions at a fixed distance from the advancing apex. The pH-dependent process of augmentation requires aeration, begins without a lag period at pH 6, and is linear for 90 to 120 min. The augmentation potential of W64A(N) midzone root segments is minimal at 0.5 mM external K+ concentration and increases toward higher and lower external K+ concentrations. Augmentation is prevented at pH 4 in the Texas cytoplasmic male-sterile (T) version of inbred W64A but not in the male-fertile (N) version.Protein synthesis is required for development of K+(86Rb) uptake augmentation and probably also for maintenance of the augmented rate after development but apparently not for its expression. Inhibition of the maintenance of the augmented rate by low concentrations of chloramphenicol or cycloheximide does not prevent subsequent augmentation in their absence.Augmentation of amino acid uptake is not inhibited by 100 μg/ml chloramphenicol or 10 μg/ml cycloheximide, but augmentation of amino acid incorporation is inhibited by each. Augmentation of amino acid influx is sensitive to the toxin of Helminthosporium maydis, race T, in T roots but not in N roots, whereas augmentation of amino acid incorporation is only slightly more toxin-sensitive in T than in N root segments.