Morphological and lethal effects of mitomycin-C, N-methyl-N'-nitro-N-nitrosoguanidine, benzo(a)pyrene and 4-nitroquinoline-1-oxide on a large unicellular indicator organism, Closterium ehrenbergii (green alga)

The morphological and lethal effects of the mutagens such as mitomycin C (MMC), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), benzo(a)pyrene (BaP) and 4-nitroquinoline 1-oxyde (4NQO) on both asexual (AR) and sexual reproduction (SR) of Closterium ehren-bergii were examined. Dimethyl sulfoxide (DMSO) was used as a solvent for MNNG, BaP and 4NQO at 0.03 %, the highest concentration which was not toxic to the alga. When MMC was administrated, the size of the vegetative cells increased by about 40 % at 10 - 30 mg/l. When MNNG was added, vacuoles appeared inside the cells at 3 mg/l became larger at higher concentrations, and many morphologically abnormal gametes were observed at 0.1 - 3 mg/l. When treated with BaP, the cells grew up to 2.5 mp/l which was the highest concentration of BaP soluble in DMSO, and the frequencies of the normal zygote formation decreased and those of the abnormal seemed to increase gradually at as low as 8 x 10(-3) mg/l, When 4NQO was added, the cells stopped growing at 8 x 10(-5) mg/l. In SR, the frequencies of the normal zygote formation decreased and those of the abnormal zygote formation or zygote forming gametes increased at 2.5 - 8 x 10(-2) mg/l, When the susceptibility of C. ehrenbergii to the mutagens was compared with that of Bacillus subtilis, the former was more susceptible than the latter (e.g., 9800 times in BaP) except for the case in MMC. Copyright (C) 1996 IAWQ.