Ammonium stress in Arabidopsis: signaling, genetic loci, and physiological targets

• We review genetic loci, signaling pathways, and physiological targets of NH4+ stress in the model system Arabidopsis thaliana.
• Differing NH4+ stress responses between belowground and aboveground sources are dissected.
• New experimental approaches to the study of NH4+ toxicity are outlined.
• An integrated view of behavior and signaling in response to NH4+ stress is proposed.

Ammonium (NH4+) toxicity is a significant ecological and agricultural issue, and an important phenomenon in cell biology. As a result of increasing soil nitrogen input and atmospheric deposition, plants have to deal with unprecedented NH4+ stress from sources below and above ground. In this review, we describe recent advances in elucidating the signaling pathways and identifying the main physiological targets and genetic loci involved in the effects of NH4+ stress in the roots and shoots of Arabidopsis thaliana. We outline new experimental approaches that are being used to study NH4+ toxicity in Arabidopsis and propose an integrated view of behavior and signaling in response to NH4+ stress in the Arabidopsis system.