620 Journal of Applied Sciences Research, 9(1): 620-626, 2013 ISSN 1819-544X This is a refereed journal and all articles are professionally screened and reviewed ORIGINAL ARTICLES Corresponding Author: Fawzia I. Mohamed, Department of Genetics and Cytology, National Research Centre, Dokki, Giza, Egypt. E-mail: adam_fwz@yahoo.com. Modulatory effect of Nigella sativa extract on Vicia faba L. toxicity induced by potassium dichromate Fawzia I. Mohamed Department of Genetics and Cytology, National Research Centre, Dokki, Giza, Egypt ABSTRACT Hexavalent chromium trioxide Cr 6+ is the most active biologically, because it is capable of passing through cell membranes. It induces oxidative stress and lead to formation of stable Cr-DNA adducts that contribute to its cytotoxic and genotoxic effects. In the present study, the antigenotoxic effects of Nigella sativa extract was evaluated using the Vicia faba root chromosomal aberrations assay against potassium dicromate. Roots were given five kinds of treatments. In treatment, roots were first treated with distilled water (control). The second treated with crud extract of Nigella sativa .The third treated with different concentrations of K 2 Cr 2 O 7 (10,25,50,100 and 200mg/L) for 6 hr. In simultaneous treatment, fourth group the root -tips were treated with different concentrations with K 2 Cr 2 O 7 and N.s. extract simultaneously for 6 hr. In post-treatment roots were treated with different concentrations of K 2 Cr 2 O 7 followed by N.s. extracts. The mitotic index was generally reduced in the treated roots with the different concentrations of k 2 Cr 2 O 7 . It reached the lowest value as 3.12% after treatment with 200mg/L K 2 Cr 2 O 7 compared with the control. The limit of mitotic inhibition reached to 71.76%. The increased number of chromosomal aberrations like stickiness, laggards, chromosome bridges, C- metaphase, fragmentation and micronuclei cells were observed with the increasing concentrations of K 2 Cr 2 O 7 . The effects of post- and simultaneous treatment of N.s. extracts resulted decrease the chromosomal aberrations frequency and mitotic activity. The results indicated the repair role of Nigella sativa extract against potassium dichromate injuries during Vicia faba L. mitosis. Key words: Chromium, Nigella sativa, Vicia faba, Antigenotoxic, Mitotic division. Introduction Pollution of water is a major environmental problem facing the modern world. The global heavy metal pollution is increasing in the environment due to increase in number of industries. Many industrial wastewaters contain heavy metals like cadmium, lead, zinc, cobalt and chromium. Among heavy metals, chromium plays a major role in polluting our water environment. Chromium can co- exist in the environment in two oxidation states viz., trivalent chromium and hexavalent chromium. The hexavalent chromium is released from various industries such as electroplating, leather tanning, textile printing, textile preservation and metal finishing. The compounds of chromium have been known to be strong carcinogens and mutagens that can reach the target organs of human through drinking water. The chromium element in very low amounts is useful for organisms but at higher concentrations, it is toxic and considered as a pollutant. Chromium (Cr) is often admixed with industrial effluents that are used for irrigation. The uptake of excess concentrations of heavy metals, reduced the growth of plants(Abdel-Azeem and El-Nahas,1996). Thus, Cr loaded effluent used for irrigation disrupts several physiological and cytological processes in cells. Shanker et al., (2005) found that chromium reduced root growth, biomass, seed germination, early seedling development and induces chlorosis, photosynthetic impairment and finally leading to plant death (Seoccianti et al., 2006; Chidambaram et al., 2009 and Akini and Akini, 2010). Several in vivo and in vitro studies showed that chromium compounds caused damage DNA in a variety of ways, including DNA single and double-strand breaks (SDSBs) generating chromosomal aberrations, micro- micro-nucleus formation, sister chromatid exchanges, formation of DNA adducts and alteration in DNA replication and transcription (O'Brien et al., 2001 and Matsumoto et al., 2003). Plants and plant extracts are inescapable part of many of them exhibit valuable medicinal properties. In the recent years, there has been an increasing interest in antimutagenesis (Calomme, 1996) and antioxidant activity (Yagi et al., 2002). These components may be useful in preventing cancer and other mutation related diseases by fortifying physiological defense mechanisms (De Flora, 1996). Antimutagenic agents are natural or synthetic compounds capable of lowering the frequency of mutation by diverse mechanisms .(De Flora and Ramel, 1988).