Radial Transport of Ions in Roots

Measurements were made of the relative amounts of (86)Rb, (36)Cl, and (32)P accumulated in the cortex and stele of intact roots of corn (Zea mays), either detached or attached to their shoots. Both 4- and 7-day-old roots accumulated as much or more (86)Rb in the stele as in the cortex. In experiments with (36)Cl, cortex and stele accumulated the same amount, except for 4-day-old and 7-day-old attached roots, in which the cortex contained more (36)Cl than the stele after 23 hr. An additional study of (32)P uptake showed greater accumulation in the cortex than the stele for a short period of time, but as much in the stele as in the cortex after 8 to 24 hr. Transport of (86)Rb, (36)Cl, and (32)P into the xylem exudate increased with increasing accumulation of these ions in stele and cortex of the root. These experiments show no consistent difference between cortex and stele of intact corn roots with respect to their ability to accumulate several kinds of ions.