Arabidopsis thaliana root non‐selective cation channels mediate calcium uptake and are involved in growth

Abstract

SummaryCalcium is a critical structural and regulatory nutrient in plants. However, mechanisms of its uptake by root cells are poorly understood. We have found that Ca 2þ influx in Arabidopsis root epidermal protoplasts is mediated by voltage-independent rapidly activating Ca 2þ -permeable non-selective cation channels (NSCCs). NSCCs showed the following permeability (P) sequence: P Ca (1.00) ¼ P Ba (0.93) > P Zn (0.51), P Ca / P Na ¼ 0.19, P Ca /P K ¼ 0.14. They were inhibited by quinine, Gd 3þ , La 3þ and the His modifier diethylpyrocarbonate, but not by the Ca 2þ or K þ channel antagonists, verapamil and tetraethylammonium (TEA þ ). Single channel conductance measured in 20 mM external Ca 2þ was 5.9 pS. Calcium-permeable NSCCs co-existed with hyperpolarisation-activated Ca 2þ channels (HACCs), which activated 40-60 min after forming the whole-cell configuration. HACCs activated at voltages <À130 to À150 mV, showed slow activation kinetics and were regulated by cytosolic Ca 2þ ([Ca 2þ ] cyt ). Using aequorin-expressing plants, a linear relationship between membrane potential (V m ) and resting [Ca 2þ ] cyt was observed, indicating the involvement of NSCCs. Intact root 45 Ca 2þ influx was reduced by Gd 3þ (NSCC blocker) but was verapamil and TEA þ insensitive. In the root elongation zone, both root net Ca 2þ influx (measured by Ca 2þ -selective vibrating microelectrode) and NSCC activity were increased compared to the mature epidermis, suggesting the involvement of NSCC in growth. A Ca 2þ acquisition system based on NSCC and HACC co-existence is proposed. In mature epidermal cells, NSCC-mediated Ca 2þ influx dominates whereas in specialised root cells (root hairs and elongation zone cells) where elevated [Ca 2þ ] cyt activates HACCs, HACC-mediated Ca 2þ influx predominates.

Fluorescence Resonance Energy Transfer-Sensitized Emission of Yellow Cameleon 3.60 Reveals Root Zone-Specific Calcium Signatures in Arabidopsis in Response to Aluminum and Other Trivalent Cations

“…However, the significance of the Al 3+ -induced biphasic [Ca 2+ ] cyt response is unclear. From our results, it seems likely that the first Al 3+ -induced [Ca 2+ ] cyt peak is linked to Ca 2+ influx across the plasma membrane through Ca 2+ -permeable channels (Demidchik et al, 2002;Miedema et al, 2008) and that the second peak is triggered by the release of Ca 2+ from internal stores (e.g. vacuole, endoplasmic reticulum, mitochondria, or plastids; Trewavas and Malhó, 1998;Sanders et al, 2002;Nomura et al, 2008).…”

“…However, one possibility is that cells from each root developmental region differ in their efficiency in removing Ca 2+ because of differences in the expression of Ca 2+ -ATPases in the plasma membrane and/or endoplasmic reticulum and Ca 2+ /H + exchangers in the plasma membrane and tonoplast (Sze et al, 2000;Sanders et al, 2002). Another possibility is that cells in the different root regions express certain receptor proteins that perceive the applied chemical signal, which in turn activate a specific type of Ca 2+ channel (Kiegle et al, 2000a currents in plants (Kiegle et al, 2000a;Demidchik et al, 2002;Qu et al, 2007) Fig. S3B) might be indicative of responses of nongrowing cells like those observed in the mature zone or differential effects on specific cell types (Figs.…”

“…6C) To further characterize the nature of the biphasic [Ca 2+ ] cyt response to Al 3+ , we pretreated the roots with reagents that block Ca 2+ channels or chelate Ca 2+ from the external medium. We first utilized verapamil, which is known to block plasma membrane voltagedependent Ca 2+ channels (Demidchik et al, 2002). Roots pretreated with the solvent control solution for 20 min and then with Al 3+ displayed the typical Al 3+ -induced biphasic [Ca 2+ ] cyt response (Fig.…”

“…[Ca 2+ ] cyt fluctuations occur because cells have a Ca 2+ signaling "toolkit" (Berridge et al, 2000) composed of on/off switches and a multitude of Ca 2+ -binding proteins. The on switches depend on membrane-localized Ca 2+ channels that control the entry of Ca 2+ into the cytosol Tester, 1995, 1997;Thion et al, 1998;Kiegle et al, 2000a;White et al, 2000;Demidchik et al, 2002;Miedema et al, 2008). On the other hand, the off switches consist of a family of Ca 2+ -ATPases and Ca 2+ /H + exchangers in the plasma membrane or endomembrane that remove Ca 2+ from the cytosol, bringing the [Ca 2+ ] cyt down to the initial resting level (Lee et al, 2007;Li et al, 2008).…”

Receptor-Like Activity Evoked by Extracellular ADP in Arabidopsis Root Epidermal Plasma Membrane

“…Experiments were performed within the first 20 to 30 min of recording so that extracellular ADP-activated currents could be distinguished from the time-dependent development of the constitutive hyperpolarization-activated Ca 2+ -permeable conductance. The latter becomes the dominant Ca 2+ conductance in this cell type after approximately 1 h (Demidchik et al, 2002).…”