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doi: 10.1242/10.1242/jcs.00201

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Free oxygen radicals regulate plasma membrane Ca²⁺- and K⁺-permeable channels in plant root cells

¹ Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK
² School of Agricultural Sciences, University of Tasmania, Hobart, Tasmania 7001, Australia

View larger version (29K): [in a new window]   Fig. 1. Hydroxyl-radical-induced whole cell outward K+ (Kout) and inward Ca2+ (Cain) currents in protoplasts from Arabidopsis root mature epidermis. (A) Whole cell control currents. (B) Whole cell currents from the same protoplast after 15 minutes exposure to 1 mM Cu2+/ascorbate (Cu/a). (c) Mean (±s.e.m.) current-voltage curves.

View larger version (26K): [in a new window]   Fig. 2. Observations on the OH•-induced Kout and Cain in protoplasts from Arabidopsis root mature epidermis. (A) Mean (±s.e.m.) time-courses of OH•-induced Kout and Cain measured at +80 and -160 mV, respectively; 1 mM Cu/a added at 0 minutes. (B) The effect of omitting K+ from the pipette solution (-K) or reducing bathing solution Ca2+ to 0.2 mM (-Ca) on currents measured 15 minutes after addition of 1 mM Cu/a (representative current-voltage curves). (C) Pharmacology of OH•-induced Kout and Cain (20 mM TEA+, 50 µM La3+, 50 µM Gd3+, 20 µM verapamil, 20 mM Ca2+, 20 mM Ba2+).

View larger version (30K): [in a new window]   Fig. 3. Hydroxyl radical effects on Arabidopsis root pericycle protoplasts. (A) Whole cell currents before exposure (control). (B) Whole cell currents after 30 minutes exposure to 1 mM Cu2+/ascorbate (Cu/a). (C) Mean (±s.e.m.) current-voltage curves.

View larger version (29K): [in a new window]   Fig. 4. Hydroxyl radical effects on Arabidopsis root elongation zone epidermal protoplasts. (A) Whole cell currents before exposure (control). (B) Whole cell currents after 15 minutes exposure to 1 mM Cu2+/ascorbate (Cu/a). (C) Mean (±s.e.m.) current-voltage curves.

View larger version (17K): [in a new window]   Fig. 5. Hydroxyl radical effects on Arabidopsis root fluxes. (A) Mean (±s.e.m.) time course of K+ release from Columbia roots. (B) Root cell OH•-induced [Ca2+]cyt increase measured using cytosol-targeted aequorin. Data were obtained with 1 and 10 mM ambient Ca2+; 1 mM Cu/a was added as indicated by the arrow. (C) Effect of 30 minutes exposure to test compounds on OH•-induced [Ca2+]cyt increase. Concentrations in mM.

View larger version (19K): [in a new window]   Fig. 6. Hydroxyl radical effects on epidermal root fluxes of different species. (A) Representative traces of OH•-induced net K+ efflux measured by MIFETM from mature epidermal cells of different species. Initial flux values are shown as dotted lines. The 1 mM Cu/a was added as indicated by arrows. (B) Hydroxyl radical-induced net Ca2+ influx measured by MIFETM simultaneously with K+ efflux. Control Ca2+ fluxes before Cu/a addition were negligible (up to 100 times smaller) in comparison with OH•-induced influxes. Mean values (±s.e.m.) are maximal Ca2+ influx between 2 to 40 minutes exposure to 1 mM Cu/a.