Polyamines Interact with Hydroxyl Radicals in Activating Ca2+ and K+ Transport across the Root Epidermal Plasma Membranes

Reactive oxygen species (ROS) are integral components of the plant adaptive responses to environment. Importantly, ROS affect the intracellular Ca 2+ dynamics by activating a range of nonselective Ca 2+ -permeable channels in plasma membrane (PM). Using patch-clamp and non-invasive ion-selective MIFE techniques, we have characterized ionic currents and net K + and Ca 2+ fluxes induced by hydroxyl radicals (OH • ) in pea ( Pisum sativum ) roots. OH • , but not H 2 O 2 , activated a rapid Ca 2+ efflux, and a more slowly developing net Ca 2+ influx concurrent with a net K + efflux. In isolated protoplasts OH • evoked a non-selective current, with a time course and a steady-state magnitude similar to those for a K + efflux in intact roots. This current displayed a low ionic selectivity, and was permeable to Ca 2+ . Active OH • -induced Ca 2+ efflux in roots was suppressed by the PM Ca 2+ -pump inhibitors eosine yellow and erythrosine B. Cation channel blockers gadolinium, nifedipine, and verapamil, and anionic channel blockers 5-nitro-2(3-phenylpropylamino)-benzoate and niflumate inhibited OH • -induced ionic currents in root protoplasts, and K + efflux and Ca 2+ influx in roots. Contrary to expectations, polyamines (PAs) did not inhibit the OH • -induced cation fluxes. The net OH • -induced Ca 2+ efflux was largely prolonged in the presence of spermine, and all PAs tested (spermine, spermidine or putrescine) accelerated and augmented the OH • -induced net K + efflux from roots. The latter effect was also observed in patch-clamp experiments on root protoplasts. We conclude that PAs interact with ROS to alter intracellular Ca 2+ homeostasis by modulating both Ca 2+ influx and efflux transport systems at the root cell PM.