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Arabidopsis thaliana root non‐selective cation channels mediate calcium uptake and are involved in growth
Author(s) -
Demidchik Vadim,
Bowen Helen C.,
Maathuis Frans J.M.,
Shabala Sergey N.,
Tester Mark A.,
White Philip J.,
Davies Julia M.
Publication year - 2002
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.1365-313x.2002.01467.x
Subject(s) - verapamil , biophysics , calcium , channel blocker , tetraethylammonium , chemistry , aequorin , ionomycin , root hair , uniporter , voltage dependent calcium channel , biochemistry , cytosol , potassium , biology , enzyme , organic chemistry , gene
Summary 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 Ca 2+ influx in Arabidopsis root epidermal protoplasts is mediated by voltage‐independent rapidly activating Ca 2+ ‐permeable non‐selective cation channels (NSCCs). NSCCs showed the following permeability ( P ) sequence: P Ca (1.00) = P Ba (0.93) > P Zn (0.51), P Ca / P Na = 0.19, P Ca / P K = 0.14. They were inhibited by quinine, Gd 3+ , La 3+ and the His modifier diethylpyrocarbonate, but not by the Ca 2+ or K + channel antagonists, verapamil and tetraethylammonium (TEA + ). Single channel conductance measured in 20 m m external Ca 2+ was 5.9 pS. Calcium‐permeable NSCCs co‐existed with hyperpolarisation‐activated Ca 2+ 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 Ca 2+ ([Ca 2+ ] cyt ). Using aequorin‐expressing plants, a linear relationship between membrane potential ( V m ) and resting [Ca 2+ ] cyt was observed, indicating the involvement of NSCCs. Intact root 45 Ca 2+ influx was reduced by Gd 3+ (NSCC blocker) but was verapamil and TEA + insensitive. In the root elongation zone, both root net Ca 2+ influx (measured by Ca 2+ ‐selective vibrating microelectrode) and NSCC activity were increased compared to the mature epidermis, suggesting the involvement of NSCC in growth. A Ca 2+ acquisition system based on NSCC and HACC co‐existence is proposed. In mature epidermal cells, NSCC‐mediated Ca 2+ influx dominates whereas in specialised root cells (root hairs and elongation zone cells) where elevated [Ca 2+ ] cyt activates HACCs, HACC‐mediated Ca 2+ influx predominates.