Polyamines cause plasma membrane depolarization, activate Ca-, and modulate H-ATPase pump activity in pea roots

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 Ca and H transport and membrane potential in pea roots. Externally applied spermine or putrescine (1mM) equally activated eosin yellow (EY)-sensitive Ca 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 Ca pump imports 2 H per each exported Ca. Suppression of the Ca pump by EY diminished putrescine-induced net H efflux instead of increasing it. Thus, activities of Ca and H pumps were coupled, likely due to the H-pump inhibition by intracellular Ca. 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 Gd, was insensitive to anion channels' blocker niflumate, and was dependent on external Ca. Further analysis showed that uptake of polyamines but not polyamine-induced cationic (KCaH) fluxes were a main cause of membrane depolarization. Polyamine increase is a common component of plant stress responses. Activation of Ca efflux by polyamines and contrasting effects of polyamines on net H fluxes and membrane potential can contribute to Ca signalling and modulate a variety of transport processes across the plasma membrane under stress.