Modulation of mutagen-induced genotoxicity by vitamin C and medicinal plants in Allium cepa L.

Three concentrations (mg ml(-1)) of extracts of the medicinal plants Xysmalobium undulatum (XU) roots (0.125, 0.25, 0.50), leaves of Helichrysum caespititum (HC) (0.00625, 0.0125, 0.025) and ascorbic acid (AA) (0.125, 0.25, 0.50) were assessed for cytotoxicity (CT), genotoxicity (GT) and modulation of cyclophosphamide- and EMS-induced GT using the Allium cepa assay following 24 h treatment. CP (1.00 mg ml(-1)) and EMS (0.0375 mg ml(-1)) were not cytotoxic but genotoxic. CT was measured by the mitotic index (MI). GT was the number of aberrant cells per 100 mitotic cells. The MI and GT of test groups were compared with the negative control group using t-test. The modulatory effect (ME), calculated as (B - C) - (A - C)/(A - C) gave the number of times of the mutagen-induced GT by which the GT of the mutagen was reduced (anti-GT) or increased (synergism). One or more concentrations of AA, XU and HC and their mixtures with CP or EMS were cytotoxic and genotoxic. Mixtures of AA, XU and HC with CP were significantly more genotoxic than CP alone which indicated a synergistic interaction. Mixtures of AA with EMS were significantly more genotoxic than EMS alone. Mixtures of XU with EMS were less genotoxic than EMS, but not significantly, which made XU mildly anti-genotoxic to EMS GT. Mixtures of lower concentrations of HC with EMS were more genotoxic than EMS alone but not significantly. The most common aberrations among dividing cells were sticky chromosomes, c-metaphase, anaphase and telophase bridges, chromosome fragment and multipolar anaphase and telophase.