Potassium Transport in Non-Growing Corn Root Tissue as Affected by IAA and GA3

Experiments were done to determine if the spontaneous recoveryof non-growing segments of corn root (Zea mays L.) from excisioninjury is dependent on auxin. Washing the segments with 5 runindoleacetic acid (IAA) for 2 to 4 hours gave a small but significantincrease in K⁺ (⁸⁶Rb) influx, used here as a parameter reflectingrecovery of electrogenie H⁺-efflux pumping. This promotive effectwas obtained only after an hour of washing, and was sustainedby 100 nm gibberellic acid (GA₃). Any early responses to auxinwere obscured by an adverse reaction of the root cells to externalIAA which resulted in a transitory inhibition of H⁺ pumpingand K⁺ influx. Pretreatment of excised root tips with 10 µM IAA in thegrinding medium protected a plasmalemma-enriched fraction ofthe microsomes during isolation, giving increased uncoupler-sensitiveATPase activity. Non-growing root tissue thus shows three responses to auxin:an adverse reaction at the outer surface of the plasmalemmawhich blocks H⁺ pumping; a protective or restorative effecton the H⁺-ATPase; an increased capacity for K⁺ influx duringthe developmental phase of washing, which is augmented by thepresence of GA₃. (Received March 31, 1986; Accepted September 8, 1986)