THE IMPROVED ALLIUM VICIA ROOT-TIP MICRONUCLEUS ASSAY FOR CLASTOGENICITY OF ENVIRONMENTAL-POLLUTANTS

The meristematic mitotic cells of plant roots are appropriate and effi cient cytogenetic materials for the detection of clastogenicity of env ironmental pollutants, especially for in situ monitoring of water cont aminants. Among several cytological endpoints in these fast dividing c ells, such as chromosome/chromatid aberrations, sister-chromatid excha nges and micronuclei, the most effective and simplest indicator of cyt ological damage is micronucleus formation. Although the Allium cepa an d Vicia faba root meristem micronucleus assays (Allium/Vicia root MCN) have been used in clastogenicity studies about 12 times by various au thors in the last 25 years, there is no report on the comparison of th e efficiency of these two plant systems and in different cell populati ons (meristem and F-1) of the root tip as well as under adequate recov ery duration. In order to maximize the efficiency of these bioassays, the current study was designed to compare the Allium and the Vicia roo t MCN assays on the basis of chromosome length, peak sensitivity of th e mitotic cells, and the regions of the root tip where the MCN are for med. The total length of the 2n complement of Allium chromosomes is 14 .4 mu m and the total length of the 2n complement of Vicia is 9.32 mu m. The peak sensitivity determined by serial fixation at 12-h interval s after 100 R of X-irradiation is 44 h. The slope of the X-ray dose-re sponse curve of Allium roots derived from the meristematic regions was lower than that derived from cells in the F-1 region. Higher efficien cy was also demonstrated when the MCN frequencies were scored from the F-1 cells in both Allium and Vicia treated with formaldehyde (FA), mi tomycin C (MMC), and maleic hydrazide (MH). The results indicated that scoring of MCN frequencies from the F-1 cell region of the root tip w as more efficient than scoring from the meristematic region. The X-ray linear regression dose-response curves were established in both Alliu m and Vicia cell systems and the coefficients of correlations, slope v alues were used to verify the reliability and efficiency of these two plant cell systems. Based on the dose-response slope value of 0.894 fo r Allium and 0.643 for Vicia, the Allium root MCN was a more efficient test system. The greater sensitivity of the Allium roots is probably due to the greater total length of the diploid complement and the high er number of metacentric chromosomes. The Allium/Vicia root MCN test s ystem was applied to determine the clastogenicity of saccharin (SC) an d wastewater from Rio Queretaro and the Arena canal in the city of Que retaro, Mexico. The minimum effective dose (MED) is 10 R for X-rays, 5 0 mM for FA, 2.2 mM for MMC, 0.01 mM for MH, and 40 ppm for SC.