It is well-known that essential heavy metals like copper (Cu), mainly at higher concentrations usually cause overproduction of reactive oxygen species (ROS) resulting in oxidative stress in plants. Till date many experiments were carried out to evaluate how Cu toxicity influences in adult plants but only a few reports are available about the effects during germination. Since this is a very sensitive period and the effects of heavy metal stress are more serious. The aims of our study were to investigate potential oxidative stress and antioxidative defense mechanisms beside potential morphological and/or anatomical alterations in germinating seeds of Indian mustard (Brassica juncea L.) exposed to excess Cu. The following parameters were evaluated to describe oxidative stress: FRAP (ferric reducing ability of plasma), lipid peroxidation (LP), reduced glutathione content (GSH), total protein content and the activity of glutathione-S-transferase (GST), superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPOX) and glutathione reductase (GR). We also made an assessement of histochemically LP and the loss of plasma membrane integrity in the root tips, the production of callose and the lignification of cell walls. Our results showed that Cu treatments were followed by notable GSH-depletion. We could detect LP histochemically in the root tips. The application of Cu increased the activity of SOD in time and dose-dependent manner. The activity of CAT and GPOX increased after 48-96h Cu excess. Morphological symptoms of metal toxicity occurred such as stunted, hooked-formed and brownish root tips. Production of callose and lignification of cell walls could be visualized, too.
Key words: copper stress, Brassica juncea L., germination, oxidative stress, callose, lignin.
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