Photodynamic action and post-irradiation modifying effects of methylene blue and acridine orange in barley and Vicia faba

Abstract

1. Methylene blue has been demonstrated to be a potent chromosome-breaking agent in the presence of light and oxygen, using Hordeum vulgare and Vicia faba as test systems. Damage caused by methylene blue differed from that caused by acridine orange, quantitatively and qualitatively. Both caused mitotic inhibition. 2. The distribution of chromosome breaks resulting from methylene blue treatment was non-random, and centromeres and some other sites were affected preferentially. A possible mechanisms of these localised effects is discussed. 3. Post-treatments with methylene blue and acridine orange in the dark without oxygen, modified the radiation-induced two-break chromosome aberrations by a factor of 1.5 and 1.3 respectively. 4. The post-treatment of irradiated seeds by methylene blue increased chlorophyll mutation frequency by a factor of 5 in a segregating X₂ population. No modifying effect was found with acridine orange.