Polyamines cause plasma membrane depolarization, activate Ca2+-, and modulate H+-ATPase pump activity in pea roots
Pottosin, I and Velarde-Buendia, AM and Bose, J and Fuglsang, AT and Shabala, S, Polyamines cause plasma membrane depolarization, activate Ca2+-, and modulate H+-ATPase pump activity in pea roots, Journal of Experimental Botany, 65, (9) pp. 2463-2472. ISSN 0022-0957 (2014) [Refereed Article]
Polyamines regulate a variety of cation and K+ channels, but their potential effects on cation-transporting ATPases are underexplored. In this work, noninvasive microelectrode ion flux estimation and conventional microelectrode techniques were applied to study the effects of polyamines on Ca2+ and H+ transport and membrane potential in pea roots. Externally applied spermine or putrescine (1mM) equally activated eosin yellow (EY)-sensitive Ca2+ pumping across the root epidermis and caused net H+ influx or efflux. Proton influx induced by spermine was suppressed by EY, supporting the mechanism in which Ca2+ pump imports 2 H+ per each exported Ca2+. Suppression of the Ca2+ pump by EY diminished putrescine-induced net H+ efflux instead of increasing it. Thus, activities of Ca2+ and H+ pumps were coupled, likely due to the H+-pump inhibition by intracellular Ca2+. Additionally, spermine but not putrescine caused a direct inhibition of H+ pumping in isolated plasma membrane vesicles. Spermine, spermidine, and putrescine (1mM) induced membrane depolarization by 70, 50, and 35 mV, respectively. Spermine-induced depolarization was abolished by cation transport blocker Gd3+, was insensitive to anion channelsí blocker niflumate, and was dependent on external Ca2+. Further analysis showed that uptake of polyamines but not polyamine-induced cationic (K++Ca2++H+) fluxes were a main cause of membrane depolarization. Polyamine increase is a common component of plant stress responses. Activation of Ca2+ efflux by polyamines and contrasting effects of polyamines on net H+ fluxes and membrane potential can contribute to Ca2+ signalling and modulate a variety of transport processes across the plasma membrane under stress.