engleski

Accumulation of uranium (U) and its phytotoxicity symptoms in Pisum sativum L.

Environmental contamination caused by uranium (U) and other radionuclides is a serious concern worldwide, especially due to anthropogenic activities. Ultimate accumulation of released U in aquatic systems and soils represent an escalating problem for all living organisms including humans. The toxic effects of U in living organisms depend on uranyl ion speciation and their solubility. Hydroponically grown pea plants (Pisum sativum L.) were treated with 25 and 50 µM of uranium for five days. After the treatment for 5 days, we studied the impact of U on photosynthetic pigments (chlorophyll/carotenoid contents) and some antioxidants such as superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR) and the cysteine (CYS) and non-protein thiol (NP-SH), as well as lipid peroxidation (LPO) as oxidative-damage markers. Disturbances in nutrient status induced by U are another feature previously noted in other plants. It has been also observed that ion transporters could be the target of ROS hence, U uptake was also studied by analyzing the content in roots and leaves of Pisum sativum plants. In tested plants photosynthetic pigments significantly altered depending on the concentration of U uptake in comparison to control, the decrease in net photosynthesis as a consequence of reduced absorption of essential mineral nutrients is an indirect reason for plant chlorosis. SOD isozymes (Mn- SOD and Cu, Zn-SOD) were higher in control shoots in comparison to treatment. CAT and GR activity was lower in roots and shoots in compare to control at higher concentration but it was interesting to note that both CYS and NP-SH (insignificant) was higher in root as well as in shoots in higher concentration U treated plants. The decline in CAT activity might be due to the inhibition of the enzyme by post-transcriptional alterations or down- regulation of gene expression. The increase in the level of thiols and CYS may be due to stimulation of enzymes of sulfate reduction pathway such as APS reductase and Serine acetyltransferase. The enhancement in NP-SH concentration possibly also reflects a defence reaction to enhanced production of ROS. Increment in LPO indicates the prevalence of oxidative stress and perhaps this may be one of the possible mechanisms by which toxicity due to U could be manifested in the plant tissues. However, the level of LPO was lower in roots as compared to that of shoots. This was attributed to low U load in shoots that probably resulted in low oxidative stress and membrane damage. U accumulation is also higher in roots rather in shoots after 5 days of treatment. Our observation suggests that U severely disturbed the nutritional status of the experimental plant, a situation that could induce alterations in cell metabolism and thereby stunt growth. It has been hypothesized that the metal detoxification mechanism was more pronounced at the site of its uptake, which is restricting the mobility of metals to shoot from the root. The detail of this work is going to be discussed in the meeting.

Uranium ; phytotoxicity ; antioxidants ; photosynthetic pigments

nije evidentirano