Depolarization of transmembrane potential of corn and wheat coleoptiles under reduced water potential and after IAA application

Abstract

The influence of IAA and temporarily reduced water potential on the transmembrane potential (PD) of corn and wheat coleoptile sections was investigated. The studies were performed by two different methods: discontinuous PD measurements with microelectrodes in corn coleoptile sections and continuous measurements with microelectrodes in wheat coleoptile sections. Both methods showed a very rapid depolarization of PD within a period of 2 to 5 min. In corn coleoptile sections, a PD oscillation was observed within an average period of 14.5 min after IAA application and of 14.0 min after reduction of water potential. The PD amplitude was about 20 to 25 mV. In wheat coleoptile sections, an oscillation of PD could not be definitely established. After an IAA-induced depolarization period of 4 to 7 min, the initial potential sometimes was restored, while in some other cases, a subsequent hyperpolarization was found although in most cases the depolarization continued. The discussion covers the possibility that a decrease in PD caused by IAA and water stress may induce activation of H+ secretion by a plasmalemma H+ pump.