Antagonistic effects of ethyl methanesulfonate and maleic hydrazide in inducing somatic mutations in the stamen hairs of Tradescantia clone BNL 4430.

Abstract

Mutagenic interaction between ethyl methanesulfonate (EMS; a monofunctional alkylating agent) and maleic hydrazide (MH; a promutagen activated into a mutagen in plants highly likely by peroxidase) was studied in the stamen hairs of Tradescantia clone BNL 4430, a blue/pink heterozygote. Since EMS has been shown to act synergistically with X rays in inducing mutations, and mutagenic synergisms have also been observed between X rays and MH by exposing to X rays before MH treatments, EMS and MH were expected to act synergistically at least by exposing to EMS before MH treatment. Three different combined treatments were conducted, i.e., by exposing for 4 h to 18.8 mM EMS 44 or 20 h before starting or 20 h after completing 1 mM MH treatments for 4 h. Unexpectedly, however, clear antagonistic effects in inducing somatic pink mutations were detected after all these combined treatments. Especially, the induced mutation frequency by exposing to EMS 44 h before the MH treatment was significantly lower than that induced by MH alone. The clear mutagenic antagonisms observed were thought to have resulted from EMS-caused inhibition of activation of MH by peroxidase, EMS ethylating and thus inactivating this enzyme or its precursors. Decreased peroxidase activities than those after treatments with MH alone were measured after two combined treatments, i.e., 12 h after the one exposing to EMS 44 h before MH and 24 h after the other exposing to EMS 20 h after MH, but the decreases were not large enough or their fluctuations were too large to judge them to be statistically significant. Comparisons of mutation frequencies induced by the combined treatments exposing to EMS before MH with those by MH alone suggest that there are some mechanisms (other than ethylation of peroxidase or its precursors) by which EMS suppresses the activation of MH.

Further yearly analyses of spontaneous pink mutant events in the stamen hairs of Tradescantia clone BNL 4430 cultivated in the NSC growth chamber.

“…The frequency is also lower than those obtained in 1992-1995 by cultivating young inflorescence-bearing shoots with roots in the same NSC growth chamber, which ranged from 1.50 ± 0.04 to 1.56 ± 0.04 PMEs per 10 4 hair-cell divisions . The only modification in the environmental conditions between the present and earlier studies (Shima and Ichikawa, 1994Xiao and Ichikawa, 1995, 1996, 1998a, 1998b, 1998cIchikawa et al, 1995;Ichikawa and Wushur, 2000) was a minor change in the method of supplying the nutrient solution used, i.e., modified to keep the amount nearly constant, and it does not seem unlikely that this modification resulted in the significantly lower spontaneous mutation frequency. The lower background mutation frequency is helpful especially for conducting mutagenicity tests at low levels.…”

“…The nutrient solution used in the both facilities was a 1/2,500 Hyponex solution, and the solution was exchanged every 2 weeks. During the 2-week periods between the exchanges, Hyponex solution at a lower concentration (1/4,000) was added every day and every 2 days in the latter and former facilities, respectively, to keep the amount nearly constant, as the only modification in the environmental conditions compared to those in previous studies (Shima and Ichikawa, 1994Xiao and Ichikawa, 1995, 1996, 1998a, 1998b, 1998cIchikawa et al, 1995;Ichikawa and Wushur, 2000).…”

“…The system has also been shown to be suitable for studying the variation in spontaneous somatic mutation frequency (Takahashi and Ichikawa, 1976;Schairer and Sautkulis, 1982;Schairer et al, 1983;Ichikawa 1984Ichikawa , 1992Ichikawa , 1994Imai et al, 1991;Sanda-Kamigawara et al, 1991Ichikawa et al, 1995Ichikawa et al, , 1996aIchikawa et al, , 1996bIchikawa and Wushur, 2000). The use of the young inflorescencebearing shoots with roots of clone BNL 4430 cultivated in a recently developed nutrient solution circulating (NSC) growth chamber (Shima and Ichikawa, 1994;Ichikawa and Wushur, 2000) has been shown to be especially efficient for detecting mutagenic synergisms (Shima and Ichikawa, 1994Xiao and Ichikawa, 1995, 1996, 1998a, 1998b or antagonisms (Xiao and Ichikawa, 1995, 1996, 1998a, 1998c among various chemicals and X-rays, making it possible to determine spontaneous background mutation frequencies with higher accuracy than before Ichikawa and Wushur, 2000).…”

Comparative evaluation of promutagens o-PDA, m-PDA and MH for genotoxic response in root cells of Allium cepa L.

“…MH (l,2-dihydropyridazine-3,6-dione) a promutagen [3][4][5]; since its discovery has been of growing importance as an herbicide with uses including inhibition of sprouting in vegetables and stored root crops, prevention of sucker production in tobacco plants and growth control of grass, and foliage [6]. o-PDA and m-PDA are promutagenic monocyclic arylamines/aromatic amine used in the preparation of various polymers, as an important constituent of hair dyes and dyes for leather and textiles [7].…”