Arabidopsis root peroxisomes are involved in cadmium responses

Plant peroxisomes are organelles which are known to be involved in the response of plants to different environmental stresses. Despite their simple structure, they are highly versatile in morphology and abundance, and they are the site of an active ROS/RNS metabolism as well as of the biosynthesis of hormones, such as jasmonates and auxins [1]. In plant cells, peroxisome biogenesis and activity are dependent upon an array of PEROXIN (PEX) proteins importing from the cytosol peroxisomal matrix proteins carrying specific C- or N-terminal aminoacidic sequences, the Peroxisomal Targeting Signal type 1 (PTS1) or type 2 (PTS2), respectively [2]. Cadmium (Cd) is a ubiquitous contaminant whose excess in the soil affects plant development and productivity. The roots easily absorb and accumulate Cd from the soil, resulting in stunting plant growth and cellular differentiation alterations [3]. Thus, to encounter sub-lethal Cd toxicity, plant must rely on an early perception and an effective response of the root system to the pollutant, a process in which peroxisomes should play a key role [4]. To better understand the role of this important organelle in the root response to Cd toxicity, seedlings of Arabidopsis thaliana wild-type and pex7-1 mutant, with reduced PTS2 protein import [2], were grown in the presence of 30 or 60 μM Cd2+ and their primary root analysed by epifluorescence microscopy for hydrogen peroxide (H2O2) and nitric oxide (NO) contents. In addition, a morphological analysis of the root system as well as a preliminary analysis of root jasmonates and auxins contents were carried out after pollutant exposure. Finally, through a fluorescent probe labelling peroxisomes and an At35S:CFP-PTS1 transgenic line [5], was investigated how Cd affects peroxisome distribution, both in protoplasts and in entire roots.. Our findings show that size and distribution of peroxisomes are affected by Cd, but not in pex7-1, leading to disrupted NO and H2O2 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.