College of Life Science and Technology, Shanxi University, Taiyuan 030006, China
Acta Ecologica Sinica,2007,27(6):2318～2324.Abstract： Sulfur dioxide (SO₂) is a common air pollutant, which could inhibit plant growth, influence photosynthesis, and injure micro molecular in plant cells. For this reason, the chromosomal aberrations induced by hydrates of SO₂——sodium bisulfite and sodium sulfite mixture (3∶1, mmol•L^-1/ mmol•L^-1) were investigated in Vicia faba (broad bean) root tips.
Dry broad bean seeds were soaked for 24 h in distilled water at 23℃ and allowed to germinate between two layers of moist cotton. When the newly emerged roots were of 1.00-2.00 cm in length, they were used in the test. The negative control was incubated in distilled water. Bisulfite groups were exposed to bisulfite-sulfite solutions for 12 and 24 h respectively, in the range of 0.20^-15.00 mmol/l. For chromosomal aberration assay, the roots were incubated in 0.05% colchicine for 5 h, then fixed in 1∶3 (V/V) aceto-ethanol solutions. They were digested in the solution of 2.5% cellulase and pectinase, and harvested as cell suspensions. The cell suspensions were dropped on slides to make chromosomal samples. After staining with Giemsa solution, aberrations of chromosomal structure and number were examined through microscopy. For anaphase aberration assay, Vicia roots were soaked in the fixative directly after treatment. When slides prepared for microscopic examination, the roots were hydrolyzed in 1 mmol/l HCl and stained with Schiff reagent, and then mitotic zone from well-stained root tip were immersed on a clean slide and squashed under a cover glass.
Present results showed that sulfur dioxide hydrates caused aberrations of chromosomal structure and number. Frequencies of chromosomal structure aberrations, both chromatid-type aberrations and chromosome-type aberrations, increased significantly as well as aneuploid after seedlings exposed to sulfur hydrates over a range of 0.20 to 15.0 mmol/L. Deletions, fragments and other complex aberrations, such as rings (chromatid and chromosome), dicentics and translocation, were found on metaphase slides after Vicia roots exposed to the hydrates, while abnormal chromosome behavior including lagging, bridge and fragment appeared during division. These results indicated that SO₂ hydrates induced chromosomal breakage and inappropriate chromosome fuse in V. faba root tip cells, which destabilize the orderly transmission of genetic information to the next generation of cells, and lead to the destroy of genetic stability and genome instability. Results of the present study suggest that SO₂ is one of the mutagenic and clastogenic agents in the environments.