Arabidopsis thaliana root non-selective cation channels mediate calcium uptake and are involved in growth.
Calcium is a critical structural and regulatory nutrient in plants. However, mechanisms of its uptake by root cells are poorly understood. We have found that Ca2+ influx in Arabidopsis root epidermal protoplasts is mediated by voltage-independent rapidly activating Ca2+-permeable non-selective cation channels (NSCCs). NSCCs showed the following permeability (P) sequence: PCa (1.00) = PBa (0.93) > PZn (0.51), PCa/PNa = 0.19, PCa/PK = 0.14. They were inhibited by quinine, Gd3+, La3+ and the His modifier diethylpyrocarbonate, but not by the Ca2+ or K+ channel antagonists, verapamil and tetraethylammonium (TEA+). Single channel conductance measured in 20 mm external Ca2+ was 5.9 pS. Calcium-permeable NSCCs co-existed with hyperpolarisation-activated Ca2+ channels (HACCs), which activated 40-60 min after forming the whole-cell configuration. HACCs activated at voltages <-130 to -150 mV, showed slow activation kinetics and were regulated by cytosolic Ca2+ ([Ca2+]cyt). Using aequorin-expressing plants, a linear relationship between membrane potential (Vm) and resting [Ca2+]cyt was observed, indicating the involvement of NSCCs. Intact root 45Ca2+ influx was reduced by Gd3+ (NSCC blocker) but was verapamil and TEA+ insensitive. In the root elongation zone, both root net Ca2+ influx (measured by Ca2+-selective vibrating microelectrode) and NSCC activity were increased compared to the mature epidermis, suggesting the involvement of NSCC in growth. A Ca2+ acquisition system based on NSCC and HACC co-existence is proposed. In mature epidermal cells, NSCC-mediated Ca2+ influx dominates whereas in specialised root cells (root hairs and elongation zone cells) where elevated [Ca2+]cyt activates HACCs, HACC-mediated Ca2+ influx predominates.
Demidchik
Vadim
V
Department of Plant Sciences, University of Cambridge, Downing Street, UK. vd211@cam.ac.uk
Bowen
Helen C
HC
Maathuis
Frans J M
FJ
Shabala
Sergey N
SN
Tester
Mark A
MA
White
Philip J
PJ
Davies
Julia M
JM
D017920:Antiporters / Q000378:metabolism*; D017360:Arabidopsis / Q000166:cytology / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism*; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000187:drug effects; D005682:Gadolinium / Q000494:pharmacology; D015640:Ion Channel Gating; D017136:Ion Transport / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D019441:Plant Epidermis / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D018517:Plant Roots / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D011523:Protoplasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D014700:Verapamil / Q000494:pharmacology
D017920:Antiporters; D005682:Gadolinium; D014700:Verapamil; D011188:Potassium; D002118:Calcium