Calcium- and potassium-permeable plasma membrane transporters are activated by copper in Arabidopsis root tips: linking copper transport with cytosolic hydroxyl radical production

Transition metals such as copper can interact with ascorbate or hydrogen peroxide to form highly reactive hydroxyl radicals (OH^.), with numerous implications to membrane transport activity and cell metabolism. So far, such interaction was described for extracellular (apoplastic) space but not cytosol. Here, a range of advanced electrophysiological and imaging techniques were applied to Arabidopsis thaliana plants differing in their copper-transport activity: Col-0, high-affinity copper transporter COPT1-overexpressing (C1^OE) seedlings, and T-DNA COPT1 insertion mutant (copt1). Low Cu concentrations (10μm) stimulated a dose-dependent Gd³⁺ and verapamil sensitive net Ca²⁺ influx in the root apex but not in mature zone. C1^OE also showed a fivefold higher Cu-induced K⁺ efflux at the root tip level compared with Col-0, and a reduction in basal peroxide accumulation at the root tip after copper exposure. Copper caused membrane disruptions of the root apex in C1^OE seedlings but not in copt1 plants; this damage was prevented by pretreatment with Gd³⁺. Our results suggest that copper transport into cytosol in root apex results in hydroxyl radical generation at the cytosolic side, with a consequent regulation of plasma membrane OH^.-sensitive Ca²⁺ and K⁺ transport systems.