The Auxin-Nitric Oxide Highway: A Right Direction in Determining the Plant Root System

Abstract

Nitric oxide (NO) appeared as a novel signal molecule in plants at the end of the twentieth century. Since then, new discoveries on the participation ofNO in the regulation of plant biology have not stopped. One of the most yet intriguing aspects that are under strong investigation is the extension and scope of the NO involvement in the control of cell redox balance and hormone-regulated processes. In this chapter, we addressed both issues connecting root growth with the NO-mediated posttranslational modification S-nitrosylation on the auxin receptor transport inhibitor response 1 (TIR1) and on the antioxidant enzyme ascorbate peroxidase 1 (APX1). Auxin is probably the best studied plant hormone influencing root growth and development. Even if the components of the signaling cascade leading to the induction of auxin-responsive genes have been elucidated, here we describe the last findings explaining the molecular mechanisms underlying the requirement of NO to get a full response to auxin stimulus. 1