Powering the plasma membrane Ca2+-ROS self-amplifying loop

Reactive oxygen species (ROS) and intracellular Ca2+ signaling interact with and amplify each other: the major ROS-producing plasma membrane enzyme NADPH-oxidase (NOX) is activated by cytosolic Ca2+, and in turn ROS activate Ca2+ influx across the plasma membrane. For the latter, NOX-produced superoxide anions need to be converted to hydroxyl radicals. Makavitskaya et al. (2018) have now demonstrated that salt stress promotes ascorbate efflux, which, via reduction of the apoplastic copper and iron ions, assists in the generation of hydroxyl radicals, thus inducing a rise in intracellular Ca2+ in the roots.