SURVIVAL TO EARLY TOXIC COPPER EXCESS: BIOCHEMICAL AND ANATOMICAL CHANGES DURING GERMINATION OF INDIAN MUSTARD

Abstract

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. To date, many experiments were carried out to evaluate how Cu toxicity influences 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. Our study aimed to investigate potential oxidative stress and antioxidative defence mechanisms besides 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 assessed 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 a 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.