G 2 repair and the formation of chromosomal aberrations—I. The effect of hydroxyurea and caffeine on maleic hydrazide-induced chromosome damage in Vicia faba

Abstract

The potentiating effects of caffeine and hydroxyurea (HU), alone or in combination, on maleic hydrazide (MH)-induced chromosome damage were studied in root tips of Vicia faba. Rootswere exposed to 2.5 × 10 −3 M caffeine for 5 hr immediately or delayed until 5 hr after the MH treatment, and/or to 5 × 10 −3 M HU during the last 2 1 2 3 hr before fixation. The frequency of MH-induced chromatid aberrations was increased by both types of post-treatment, but whereas caffeine produced an increase of all types of aberrations without markedly influencing their relative proportions, HU affected the aberration yield not only quantitatively but also qualitatively. The largest potentiation by HU was obtained for gaps, chromatid breaks and isochromatid breaks of the non-union type, whereas chromatid exchanges and isochromatid breaks with sister union were comparatively little affected. Although a particularly dramatic enhancement was obtained when the MH-treated roots were first exposed to caffeine and then to HU, the frequency of aberrations obtained after a combined MH and caffeine treatment was not increased more by HU than that obtained after MH alone. Possible molecular mechanisms involved in the action of caffeine and HU on the formation of MH-induced chromatid aberrations are discussed.