Journal
JOURNAL OF EXPERIMENTAL BOTANY
Volume 69, Issue 14, Pages 3477-3489Publisher
OXFORD UNIV PRESS
DOI: 10.1093/jxb/ery056
Keywords
Anion channels; Arabidopsis; ascorbate transport; ascorbic acid; ascorbyl radicals; calcium signalling; hydroxyl radicals; plasma membrane; reactive oxygen species; salinity
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Funding
- Russian Science Foundation [15-14-30008]
- Russian Science Foundation [15-14-30008] Funding Source: Russian Science Foundation
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Ascorbate is not often considered as a signalling molecule in plants. This study demonstrates that, in Arabidopsis roots, exogenous L-ascorbic acid triggers a transient increase of the cytosolic free calcium activity ([Ca2+](cyt).) that is central to plant signalling. Exogenous copper and iron stimulate the ascorbate-induced [Ca2+](cyt). elevation, while cation channel blockers, free radical scavengers, low extracellular [Ca2+], transition metal chelators, and removal of the cell wall inhibit this reaction. These data show that apoplastic redox-active transition metals are involved in the ascorbate-induced [Ca2+] cyt. elevation. Exogenous ascorbate also induces a moderate increase in programmed cell death symptoms in intact roots, but it does not activate Ca2+ influx currents in patch-clamped root protoplasts. Intriguingly, the replacement of gluconate with ascorbate in the patch-clamp pipette reveals a large ascorbate efflux current, which shows sensitivity to the anion channel blocker, anthracene-9-carboxylic acid (A9C), indicative of the ascorbate release via anion channels. EPR spectroscopy measurements demonstrate that salinity (NaCl) triggers the accumulation of root apoplastic ascorbyl radicals in an A9C-dependent manner, confirming that l-ascorbate leaks through anion channels under depolarization. This mechanism may underlie ascorbate release, signalling phenomena, apoplastic redox reactions, iron acquisition, and control the ionic and electrical equilibrium (together with K+ efflux via GORK channels).
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