Variations in sodium uptake along primary roots of corn seedlings.

Entry of Na(+) into segments of the apical 8-centimeter portion of corn (Zea mays) roots was investigated and analyzed for each centimeter segment separately. Influence of temperature in the 0 C to 30 C range was well described by the Arrhenius equation [U = A exp (-Ea/RT)]. Values of A and Ea differed for each segment, tending to lessen with increasing distance from root apex. Time course of Na(+) entry was followed up to 70 minutes. Time relations of the process fit well the expression U = m [1 - exp (-nt)]. Calculated maximal uptake capacity (m) diminished with increasing distance from the apex. The data presented indicate that sodium uptake mechanisms vary qualitatively and quantitatively along corn roots. Thus, the use of entire roots for characterization of uptake mechanisms should be reassessed.