Root peroxisomes responses in Arabidopsis plants exposed to cadmium toxicity

Peroxisomes are single membrane bound organelles found in the cytoplasm of eucaryotic cells. Although their small size and simple structure, they play key roles in plant growth, development, and stress response, also showing a high versatility in morphology and abundance. In addition, peroxisomes are the site of an active ROS/RNS metabolism and signalling as well as of the biosynthesis of hormones, such as jasmonates and auxins [1]. In plant cells, peroxisome’s function is dependent upon different PEROXIN (PEX) receptors that recognize peroxisomal matrix proteins carrying specific C- or N-terminal aminoacidic sequences, the Peroxisomal Targeting Signal type 1 (PTS1) or type 2 (PTS2), respectively and traffic them form the cytosol into the peroxisomal matrix [2]. Cadmium (Cd) is a global and non-essential metal whose excessive levels in soils reduce crop yield and inhibit root development and plant growth [3]. Thus, to encounter sub-lethal Cd toxicity, plant must rely on an early and effective response of the root system to the stressor, a process in which peroxisomes should play a key role [4]. To deepen the knowledge about the role of this important organelle during the plant root responses to Cd stress, seedlings of Arabidopsis thaliana pex7-1 mutant, characterized by a low PTS2 protein import [2], were grown in the presence of 30 or 60 μM Cd2+ and their primary roots compared to the wild-type after epifluorescence and light microscopy analyses for hydrogen peroxide (H2O2), nitric oxide (NO) and superoxide anion (O2¯) contents. In addition, a morphological analysis of the root system as well as a preliminary analysis of root jasmonates and auxins contents were performed after Cd-exposure. Finally, through a fluorescent probe labelling peroxisomes and an At35S:CFP-PTS1 transgenic line [5], the peroxisome distribution in response to the pollutant, both in protoplasts and in entire roots, was investigated. Our findings show that peroxisomes size and number in the plant roots are affected by Cd, but not in pex7-1, leading to changes in ROS/RNS levels in the primary root of wild-type seedlings only. Moreover, the levels of jasmonates and auxins were altered in pex7-1 root system in response to the pollutant compared to wild-type, ultimately resulting into changes in root morphogenesis in the mutant.