Short-and long-term effects of cadmium on transmembrane electric potential (E m) in maize roots

Abstract

In this study, the effects of Cd on root growth, respiration, and transmembrane electric potential (Em) of the outer cortical cells in maize roots treated with various Cd concentrations (from 1 µM to 1 mM) for several hours to one week were studied. The Em values of root cells ranged between −120 and −140 mV and after addition of Cd they were depolarized immediately. The depolarization was concentration-dependent reaching the value of diffusion potential (ED) when the Cd concentration exceeded 100 µM. The values of ED ranged between −65 to −68 mV (−66 ± 1.42 mV). The maximum depolarization of Em was registered approx. 2.5 h after addition of Cd to the perfusion solution and in some cases, partial (Cd > 100 µM) or complete repolarization (Cd < 100 µM) was observed within 8-10 h of Cd treatment. In the time-dependent experiments (0 to 168 h) shortly after the maximum repolarization of Em a continuous concentrationdependent decrease of Em followed at all Cd concentrations. Depolarization of Em was accompanied by both increased electrolyte leakage and inhibition of respiration, especially in the range of 50 µM to 1 mM Cd, with the exception of root cells treated with 1 and 10 µM Cd for 24 and 48 h. Time course analysis of Cd impact on root respiration revealed that at higher Cd concentrations (> 50 µM) the respiration gradually declined (∼ 6 h) and then remained at this lowest level for up to 24 h. All the Cd concentrations used in this experiment induced significant inhibition of root elongation and concentrations higher than 100 µM stopped the root growth within the first day of Cd treatment. Our results suggest that Cd does not cause irreversible changes in the electrogenic plasma membrane H + ATPase because fusicoccin, an H + ATPase activator diminished the depolarizing effect of Cd on the Em. The depolarization of Em in the outer cortical cells of maize roots was the result of a cumulative effect of Cd on ATP supply, plasmalemma permeability, and activity of H + ATPase.

Effect of cadmium and lead on the membrane potential and photoelectric reaction of Nitellopsis obtusa cells

“…The effect of Cd and Pb on the E m of Nitellopsis obtusa cells observed here Table 1. may be caused by both the decrease of the PM H + -ATPase activity and the changes in plasma membrane permeability, especially for Ca 2+ and K + ions (Morse and Spanswick 1984;Małkowski et al 2005;Karcz and Kurtyka 2007). This suggestion is supported by our previous study (Małkowski et al 2005), in which we showed that the Cd ions at high concentration (1.0 mM) decreased the content of Ca 2+ in root cells of Zea mays L., and also by other authors who showed that Cd, but not Pb, induced a depolarization of the membrane potential (Llamas et al 2000;Pavlovkin et al 2006;Karcz and Kurtyka 2007) which resulted from decreased PM H + -ATPase activity Gonsalvez 1987, 1989;Burzyński and Buczek 1994;Fodor et al 1995;Astolfi et al 2003).…”

Impact of nickel on grapevine (Vitis vinifera L.) root plasma membrane, ROS generation, and cell viability

“…Alterations of the PM-H-ATPase activity can be assessed by studying changes in the E M . According to our results, the effect of Ni on E M of grapevine adventitious root epidermal cells differed from that reported for the other divalent cation, cadmium (Llamas et al 2000, Pavlovkin et al 2006, Fiala et al 2015 and mercury (Repka et al 2013). In shortterm experiments, Ni induced rapid and concentration-dependent transient depolarization of the PM in the grapevine roots indicating its entry into the cells.…”

The effect of cadmium-nickel interactions on superoxide production, cell viability and membrane potential (EM) in roots of two maize cultivars

“…One of these studies described that after adding of 100 µM Cd the mean E M value measured in DF zone in the interval of 10-20 h did not differ from that obtained in control cells in rice and barley roots [30]. On the contrary, an other study demonstrated that Cd elicited depolarization in maize cortical cells in the MZ [9,27].…”

“…Thus, alterations of the membrane permeability (increasing efflux rates) or of E M , and hence a decrease of ion influx rates, may explain the metal effects on lowered nutrient uptake. There are several reports on the effect of Cd and Ni on these parameters, but they have been studied separately and in different plants [2,22,23,27,30]. These metals, in short term experiments, depolarized cell membranes and it has been suggested that this effect could be involved in metal toxicity.…”

“…Measurements of E M were performed on single outer cortical cells of the 25 mm long apical primary root segments using standard microelectrode techniques [27]. After rinsing the roots with 0.5 mmol/L CaSO 4 , the roots were mounted in a 4 mL volume Acta Biologica Hungarica 66, 2015 plexiglass chamber and were constantly perfused (5 mL min −1 ) with bathing solution containing 0.1 mmol/L KCl, 0.1 mmol/L CaCl 2 adjusted to pH 5.5 using 0.1 mmol/L HCl and 0.01 mmol/L or 0.1 mmol/L CdCl 2 , NiCl 2 or the same concentrations together (Cd + Ni measurements).…”