Radial salt transport in corn roots.

Primary roots of solution-grown, 5-day-old or 6-day-old seedlings of corn (Zea mays L.) 10 to 14 cm in length were used to study radial salt transport. Measurements were made of the volume of root pressure exudation, salt concentration of the exudate, and rate of salt movement into the xylem exudate. The (32)P uptake, O(2) consumption, and dehydrogenase activity of the root cortex and stele also were studied.These roots produced copious root pressure exudate containing 4 to 10 times the concentration of (32)P in the external solution. Freshly separated stele from 5-day-old roots accumulated (32)P as rapidly as the cortex from which it was separated and the stele of intact roots also accumulated (32)P. Separated stele has a higher oxygen uptake than cortex. It also shows strong dehydrogenase activity with the tetrazolium test. The high oxygen consumption, (32)P uptake and strong dehydrogenase activity indicate that the cells of the stele probably play a direct role in salt transport.These data raise doubts concerning theories of radial salt transport into the xylem based on the assumption that the stele is unable to accumulate salt vigorously.