Peroxisomes are organelles that have an essentially oxidative type of metabolism. In plant peroxisomes the presence of proteases and a set of antioxidative enzymes have been demonstrated. In addition, the presence of nitric oxide synthase suggests that they are a cellular source of NO and adds new cellular functions to peroxisomes related to oxygen and nitrogen reactive species as they have the capacity to generate and release into the cytosol important signal molecules. The study of the regulation of these molecules that could mediate the inter-organellar communication is an important emerging area in plant research, which can supply more information on peroxisomal contribution throughout plant development and in plant response to different stress condition. Recent evidences indicate that in animal tissues NO regulates diverse biologic processes by directly modifying proteins. NO and RNS can oxidize, nitrate or nitrosylate proteins. S-nitrosylation refers to the binding of a NO group to a cysteine residue and it could play a central role in NO-mediated signalling. Accumulating data suggest that many proteins are S-nitrosylated by NO indicating that S-nitrosylation may be a ubiquitous post-translational modification regulating protein function. It has been shown that S-nitrosylation plays a comparable role to phosphorylation in animal cell biology and signal transduction. However, very little is known about the dimension of the physiological function of S-nitrosylation in plants. The aim of the proposed project is to assess the occurrence of S-nitrosylation in plant peroxisomes, with the identification and functional characterization of the NO-target proteins. Additionally, we propose the study of the changes in the pattern of S-nitrosylated proteins during different stress conditions that will help us to understand the functional consequences and the relevance of S-nitrosylation and the role of peroxisomes in physiological and pathophysiological conditions.