LONGITUDINAL GRADIENTS OF ION TRANSPORT IN CORN ROOTS

Excised roots of corn, 8 cm long, were mounted for collection of xylem exudate, submerged in aerated, labeled salt solutions, and left while steady-state exudation developed. After 19 hr, additional portions of the roots were removed and all apical ends which had been severed were sealed with wax. Collection of exudate samples began 1 hr later and continued for 8 hr. The results showed that removal of only 1 cm from the apex of the root reduced the output of rubidium to the exudate by as much as 74%. They also showed that the longitudinal changes in ion contribution to the exudate were not linear, but were closely correlated with the longitudinal gradient of Rb content in the root.