Thiol peptide level and proteomic changes in response to cadmium toxicity in Oryza sativa L. root.

In the present study, rice seedlings were exposed to a range of Cd concentrations (0.1 mu M, 1 mu M, 10 mu M, 100 mu M and 1 mM) for 15 days and a combination of different molecular approaches were used to evidence Cd effects and to assess the plants' ability to counteract metal toxicity. At a macroscopical level, only the highest Cd concentration (I mM) caused a complete plant growth inhibition, whereas the lowest concentrations seemed to stimulate growth. At genome level, the amplified fragment length polymorphism (AFLP) technique was applied to detect DNA sequence changes in root cells, showing that all the Cd concentrations induced significant DNA polymorphisms in a dose-dependent manner. Data also evidenced the absence of preferential mutation sites. Plant responses were analysed by measuring the levels of gluthatione (GSH) and phytochelatins (PCs), the thiol-peptides involved in heavy metal tolerance mechanisms. Results showed a progressive increase of GSH up to 10 mu M of Cd treatment, whereas a significant induction only of PC3 was detected in roots of plants exposed to 100 mu M of Cd. As suggested by the proteome analysis of root tissues, this last concentration strongly induced the expression of regulatory proteins and some metabolic enzymes. Furthermore, the treatment with 10 mu M of Cd induced changes in metabolic enzymes, but it mainly activated defence mechanisms by the induction of transporters and proteins involved in the degradation of oxidatively modified proteins