Effects of cadmium on nucleolus in root tips of Hordeum vulgare

Background: Hordeum vulgare is an economically important crop that is consumed in large quantities in the world. In a previous investigation, we found that cadmium (Cd) could induce some nucleolar materials containing the argyrophilic proteins scattered in the nuclei and located in the cytoplasm in the root tip cells of H. vulgare. However, what kinds of nucleolar proteins are affected has not been reported. In order to further confirm the cytological effects of Cd on nucleolus and nucleolar proteins, alterations in the cellular localization and expression of two major nucleolar proteins: fibrillarin and nucleolin in the root tips of H. vulgare were studied in the present investigation. Methods: Cytological effects of Cd on nucleolus were observed by silver-staining method and two nucleolarproteins: nucleolin and fibrillarin were observed and analyzed by means of indirect immunofluorescent microscopy and western blotting. Results: Results from the present investigation demonstrated that under Cd stress (cadmium chloride at 50 and 100 mu M), Cd could disturb the nucleolar cycle with the extrusion of silver-stained materials containing argyrophilic proteins from the nucleolus into the cytoplasm. Nucleolar material containing nucleolin and fibrillarin and their movement into the cytoplasm following Cd stress was detected with indirect immunofluorescence techniques. Western blotting revealed higher expression of these two major nucleoproteins in Cd-treated roots, which was consistent with the results obtained by indirect immunofluorescence. Conclusion: The findings of the present study confirm that Cd can have toxic effects on nucleolus and affect the expression of nucleolar proteins, nucleolin and fibrillarin. The data obtained here can provide valuable information for monitoring and forecast early effects of exposure to Cd in polluted environments.