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Toxic effects of different cadmium (Cd) concentrations on root tip cells of barley (Hordeum vulgare L.) for 1, 4, 12, 24, 48 and 72 h were investigated in order to better understand the mechanisms both in metal toxicity and tolerance. The results indicated that the roots were the main sites of cadmium uptakes. Cadmium ions initially entered elongation zone cells and were accumulated in this area. Then, the cadmium extends up to mature zone and down to meristem zone gradually. The degree of the cell damage in the root tips was associated with the amounts of cadmium absorption and accumulation. After cadmium ions entered meristem zone, cadmium disturbed the mechanisms controlling the organization of microtubule (MT) cytoskeleton and tubulin assembly/disassembly processes. The formation of abnormal MT arrays was formed, including discontinuous wavy MTs and short MT fragments at the cell periphery. The toxic effects resulted in a decrease of mitotic index and inducement of abnormal mitosis, inducing aberrant chromosomes, such as C-mitosis, anaphase bridges and chromosome stickiness. Therefore, MT cytoskeleton can be thought to be one of target sites of cadmium toxicity in root tip cells of plants. The direct cellular evidence of cadmium toxic effects on root tips of barley obtained here is valuable in evaluation of mechanisms both in metal toxicity and tolerance.

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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 μM), 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.