Metal-induced genotoxic adaptation in barley (Hordeum vulgare L.) to maleic hydrazide and methyl mercuric chloride.

Presoaked seeds of barley, Hordeum vulgare L., were exposed for 2 h to maleic hydrazide (MH), 5 x 10(-2) M or methyl mercuric chloride (MMCl), 10(-4) M with or without a prior conditioning with MH, 5 x 10(-3) M; MMCl, 10(-5) M; cadmium sulfate (CdSO4), 10(-4) M or zinc sulfate (ZnSO4), 10(-1) M; the interexposure time was 2 h. Subsequently as the seeds germinated a number of endpoints were measured that included mitotic index, mitotic chromosome aberrations and micronuclei (MNC) in embryonic shoot cells fixed at 32, 36, 40, 44, 48 and 52 h of recovery, and seedling height on day 7. The results demonstrated that prior conditioning exposure to MH or metals induced genotoxic adaptation to the subsequent challenge exposure to MH and MMCl. Cadmium-induced genotoxic adaptation against either MH or MMCl challenge exposure was, however, significantly prevented when the presoaked seeds were pre-exposed to buthionine sulfoximine, 10(-3) M for 2 h, thereby providing evidence that the underlying mechanism of genotoxic adaptation possibly involved phytochelatins.