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Hyperpolarization-activated calcium channels at the tip of Arabidopsis root hairs

Abstract : The root hair elongative growth phase ("tip growth"), like that of other tip-growing systems such as pollen tubes, algal rhizoids, and fungal hyphae, is associated with an apex-high cytosolic free calcium ([Ca(2+)](c)) gradient generated by a local Ca(2+) influx at the tip. This gradient has been shown to be a fundamental regulator of tip growth. Here, we have performed patch-clamp experiments at root hair apices of Arabidopsis thaliana (after localized cell wall laser ablation) to characterize the plasma membrane Ca(2+) channels implicated in the tip Ca(2+) influx. We have identified a hyperpolarization-activated Ca(2+) conductance. This conductance is selective for Ca(2+) over K(+) and Cl(-) (P(Ca)/P(K) = 15; P(Ca)/P(Cl) = 25) and is fully blocked by < 100-microM trivalent cations (La(3+), Al(3+), Gd(3+)). The selectivity sequence among divalent cations (determined by comparisons of the channel unitary conductance) is Ba(2+) > Ca(2+) (22 pS in 10 mM) approximately Mg(2+) > Mn(2+). This conductance was operative at typical growing hair apical resting membrane potentials. Moreover, it was seen to be down-regulated in growing hair subapical regions, as well as at the tip of mature hairs (known not to exhibit Ca(2+) influx). We therefore propose that this inward-rectifying Ca(2+) conductance is inherently involved in the apical Ca(2+) influx of growing hairs. The observed enhancement of the conductance by increased [Ca(2+)](c) may form part of a positive feedback system for continued apical Ca(2+) influx during tip growth.
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Contributor : Chantal Baracco <>
Submitted on : Wednesday, November 18, 2020 - 4:44:08 PM
Last modification on : Wednesday, November 18, 2020 - 4:44:09 PM

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Anne-Aliénor Véry, Julia M. Davies. Hyperpolarization-activated calcium channels at the tip of Arabidopsis root hairs. Proceedings of the National Academy of Sciences of the United States of America , National Academy of Sciences, 2000, 97 (17), pp.9801-9806. ⟨10.1073/pnas.160250397⟩. ⟨hal-03012714⟩



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