Peroxynitrite formation and function in plants

Peroxynitrite (ONOO−) is a reactive nitrogen species formed when nitric oxide (NO) reacts with the superoxide anion (O2−). It was first identified as a mediator of cell death in animals but was later shown to act as a positive regulator of cell signaling, mainly through the posttranslational modification of proteins by tyrosine nitration. In plants, peroxynitrite is not involved in NO-mediated cell death and its physiological function is poorly understood. However, it is emerging as a potential signaling molecule during the induction of defense responses against pathogens and this could be mediated by the selective nitration of tyrosine residues in a small number of proteins. In this review we discuss the general role of tyrosine nitration in plants and evaluate recent evidence suggesting that peroxynitrite is an effector of NO-mediated signaling following pathogen infection.

► Peroxynitrite is formed during the plant hypersensitive disease resistance response.
► Peroxynitrite is not a mediator of the hypersensitive cell death.
► Tyrosine protein nitration is central in peroxynitrite signaling functions.