Babourina, OK and Hawkins, B and Lew, R and Newman, IA and Shabala, SN, K+ transport by Arabidopsis root hairs at low pH, Australian Journal of Plant Physiology, 28, (7) pp. 635-641. ISSN 0310-7841 (2001) [Refereed Article]
Mechanisms underlying changed K+ uptake by plants at low pH need to be deciphered. One possibility is that K+ acquisition is under the strict control of plasma membrane potential (Em), which, in turn, is affected by external pH. To test this hypothesis, we used the microelectrode ion flux measurement (MIFE®) technique to study net K+ and H+ fluxes near Arabidopsis root hairs at different external pH, KCl concentrations and clamped Em. Lowering the solution pH led to strong H+ influx, K+ efflux and significant Em depolarisation. Addition of K+ to the bathing media caused significant net K+ uptake when external pH was over the range 5.5-6.0. At external pH below 5.0, however, correlation between K+ availability and net K+ uptake was negative. To explain this apparent paradox, measurements of net K+ and H+ fluxes from the root hair surface were performed concurrently with Em clamped at different values above and below the resting potential (approx. -180 mV). Our data revealed a strong dependence of net K+ flux on the clamping voltage. Clamping at values more negative than the resting potential caused a significant increase in K+ uptake into the root hair; clamping at less negative values (-20 and 0 mV) caused significant net K+ efflux from the cell. Qualitatively similar results were observed for net H+ flux. Our observations indicate direct control of K+ flux by changing Em, and suggest that Em depolarisation could be the main reason for the observed K+ efflux at low pH.