THE ROLE OF ROOT PERIPHERAL-TISSUES IN UPTAKE AND RADIAL TRANSPORT OFPOTASSIUM AND PHOSPHATE BY MAIZE ROOTS

To characterize the specific role of root periphery in uptake and radi al transport of ions, method of osmotic rupture of root epidermal cell s was used to exclude them from these processes. Osmotic rupture of ep idermal cells caused inhibition of uptake of both ions, magnitude of w hich was dependent on the concentration of ions in uptake medium. At l ow external concentrations of ions (up to 1 mu mol.l(-1)) osmotic rupt ure of epidermal cells inhibited uptake of phosphate and potassium up to 95% and 70%, respectively. At higher concentrations inhibition of p hosphate uptake decreased and attained 84% at 50 mu mol.l(-1) and 36% at 5 mmol.l(-1). The inhibition of potassium uptake was fully abolishe d at 5 mmol.l(-1) concentration when the potassium uptake was practica lly the same by both intact and osmotically treated roots. The selecti ve killing of epidermal cells by osmotic shock affected the pattern of phosphate uptake along the root axis. The typical uptake maximum in t he basal root zones of intact primary root was abolished and the uptak e of phosphate remained uniform in all segments along the root axis. I n comparison to potassium radial transport of phosphate was very slow in intact roots and did not exceed 10% of the total uptake during 60 m in. Under the same conditions radial transport of potassium was 2 time s higher. Osmotic rupture of epidermal cells substantially reduced rad ial transport of both ions, Maximal inhibition of phosphate transport occurred at short uptake period.