Effect of abscisic acid on membrane potential and transport of glucose and glycine in Lemna gibba G1

The membrane potential of Lemna gibba G1 was measured with a microelectrode; glucose and glycine uptake were measured with ¹⁴C-labeled substances. The membrane potential was increased by 85 mV on the average, after the plants had been pretreated with 10 M abscisic acid (ABA) for more than 30 min. This effect is not linked to the endogenous level of soluble sugars. The concentration of these soluble sugars was increased to more than 200% by pretreatment of the plants with ABA, however, the respiration of the plants was not affected. ABA stimulated uptake of glucose and glycine. Glucose- and glycine-dependent depolarization and repolarization of the membrane was altered: depolarization was less and repolarization was slower; during uptake of glycine, the first typical phase of repolarization was suppressed. The data suggest that ABA interferes with the primary steps of substrate uptake.Abbreviations ABA abscisic acid - FW fresh weight - IAA indole acetic acid - pd membrane potential difference - 1× perfusing solution (see methods) - H⁺ electrochemical proton gradient - pd solute-induced maximum depolarization of the membrane