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



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



Plant journal: for cell and molecular biology 32(5): 799-808



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 mM 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 45Ca(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.

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Accession: 003650949

Download citation: RISBibTeXText

PMID: 12472694

DOI: 10.1046/j.1365-313x.2002.01467.x


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