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Response of somatic mutation frequency in Tradescantia to exposure time and concentration of gaseous mutagens
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clone 4430 (T.hirsutiflora X T.subacaulis), and from 2.15 + 0.16 to 16.98 + 1.25 X 10 -3 per hair for non-hybrid clones of T. bracteata, T. gigantea, T. ohiensis, T. paludosa and T. subacaulis. The pink m u t a t i o n frequency per 10 s cells for three clones of T. subacaulis varied from 11.8 to 58.9. Frequencies per l 0 s stamen hair cells varied from 3.65 for one scoring of the putative hybrid clone 02 to 23.0 for y o u n g plants of the hybrid clone 4430. For the mutable clone 0106, spontaneous pink m u t a t i o n frequencies per 103 hairs varied from about 8.8 + 2.15 to 46.0 + 9.80 and per 10 s cells from 35.7 to 227.8, depending upon length of time after cuttings were made. The variation in frequencies among clones is assumed to have a genetic basis but within a clone is t h o u g h t to be influenced by such factors as age of plant or inflorescence, environmental conditions under which the plants are grown, and the year or time of year scoring was done. The variation observed with date of scoring suggests the possibility that an unidentified environmental mutagen(s) may be the causal agent(s). 1
Research s u p p o r t e d i n p a r t b y E R D A a n d i n p a r t b y N I E H S .
56 A.H. Sparrow and L.A. Schairer, Biology Department, Brookhaven National Laboratory Upton, New York 11973 (U.S.A.) Response of somatic mutation frequency in Tradescantia to exposure time and concentration of gaseous mutagens The interaction between time of exposure to and concentration of chemical mutagens determines the extent of the mutagenic response. Hence, such information is helpful in designing exposure schedules which will give the optimal mutation yield. Previous work with short term DBE exposures of clone 4430 has been extended in the present study up to 144 h at appropriate concentrations varying from 1 to 100 ppm. The resulting data on pink-celled stamen hair m u t a t i o n frequencies are expressed as mean values for the peak response period (6--10 days after exposure). Concentration (C)-response curves for each exposure period used show straight line relationships on log/log plots with slopes approaching 2. Since these data show a consistent increase in sensitivity with increasing time (T) of exposure the log/log plot of m u t a t i o n response vs T X C also exhibit a straightline relationship but with a 1.11 slope (Corr. coef. = 0.94). The mutation response frequency following the 144-h (6-day) exposure at 2 ppm of DBE was 5 events per 100 stamen hairs or equivalent to that produced by about 50 rad of X rays. Since previous experiments with clone 4430 have established statistically significant increases in m u t a t i o n rates of 0.5 per 100 hairs for DBE and 0.1 for X rays, meaningful data should be obtainable at DBE levels as low as 0.1 ppm based on extrapolations of the 144-h concentration-response and T X C curves. The sensitivity of the Tradescantia test system in this range should make it adaptable to mutagen monitoring at very low levels of
406 known or suspected mutagenic air pollutants. R e s e a r c h s u p p o r t e d in p a r t b y t h e U.S. E n e r g y R e s e a r c h and D e v e l o p m e n t A d m i n i s t r a t i o n and in p a r t b y the N a t i o n a l I n s t i t u t e of E n v i r o n m e n t a l H e a l t h S c i e n c e s .
57 C.H. Nauman, P.J. Klotz and A.H. Sparrow, Biology and Applied Science Departments, Brookhaven National Laboratory, Upton, New York 11973 (U.S.A.)
Dosimetry of tritiated 1,2-dibromoethane in floral tissues of Tradescantia Inflorescences of Tradescantia clone 4430, heterozygous for flower color, were exposed to various concentrations of gaseous tritiated 1,2-dibromoethane ([3H]DBE). The pink somatic mutation dose-response curve from a series of experiments was parallel to that determined previously for non-labeled DBE, b u t elevated due to the contribution of the beta radiation. Floral parts were dissected from buds following exposures of from 15 min to 6 h and analyzed for tissue concentration of [3H]DBE by liquid scintillation counting. The bud tissue concentration of [3H]DBE increased in proportion to the exposure concentration. Sepal, petal, anther, stamen and ovary tissues contained similar amounts of activity per mg, indicating that penetration of the chemical was uniform. Subsequent experiments, only partially analyzed at present, indicate that penetration of the gaseous DBE to inner tissues is rapid. Tissues from flowers which opened for up to 10 days after exposure retained only slightly declining amounts of radioactivity, indicating that the [3H]DBE or 3H is tightly b o u n d in the tissues. Autoradiographs of stamen hair tissue from buds show silver grains that are randomly distributed over the nucleus and cytoplasm immediately after exposure and for up to 12 days later. Thus, [3H]DBE is n o t localized within the cell. R e s e a r c h s u p p o r t e d in p a r t b y t h e U.S. E n e r g y R e s e a r c h and D e v e l o p m e n t A d m i n i s t r a t i o n and in p a r t b y t h e N a t i o n a l I n s t i t u t e of E n v i r o n m e n t a l H e a l t h S c i e n c e s .
58 S. Mittler, Northern Illinois University, DeKalb, Illinois 60115 (U.S.A.) Screening for induced chromosome loss and non-disjunction in Drosophila melanogaster Adult Drosophila males yB/scSy ÷are either injected, fed or exposed to the suspected mutagen and then mated every two days to ywf. The appearance of ywf male, the XO male was a result of a loss of X or Y chromosomes, and the exceptional wild body Bar eye female, XXY indicated a primary non-disjunction event. The brooding m e t h o d was used to assess the sensitivity of the various stages of spermatogenesis to the possible mutagen. Digitonin, a microtubule
clone 4430 (T.hirsutiflora X T.subacaulis), and from 2.15 + 0.16 to 16.98 + 1.25 X 10 -3 per hair for non-hybrid clones of T. bracteata, T. gigantea, T. ohiensis, T. paludosa and T. subacaulis. The pink m u t a t i o n frequency per 10 s cells for three clones of T. subacaulis varied from 11.8 to 58.9. Frequencies per l 0 s stamen hair cells varied from 3.65 for one scoring of the putative hybrid clone 02 to 23.0 for y o u n g plants of the hybrid clone 4430. For the mutable clone 0106, spontaneous pink m u t a t i o n frequencies per 103 hairs varied from about 8.8 + 2.15 to 46.0 + 9.80 and per 10 s cells from 35.7 to 227.8, depending upon length of time after cuttings were made. The variation in frequencies among clones is assumed to have a genetic basis but within a clone is t h o u g h t to be influenced by such factors as age of plant or inflorescence, environmental conditions under which the plants are grown, and the year or time of year scoring was done. The variation observed with date of scoring suggests the possibility that an unidentified environmental mutagen(s) may be the causal agent(s). 1
Research s u p p o r t e d i n p a r t b y E R D A a n d i n p a r t b y N I E H S .
56 A.H. Sparrow and L.A. Schairer, Biology Department, Brookhaven National Laboratory Upton, New York 11973 (U.S.A.) Response of somatic mutation frequency in Tradescantia to exposure time and concentration of gaseous mutagens The interaction between time of exposure to and concentration of chemical mutagens determines the extent of the mutagenic response. Hence, such information is helpful in designing exposure schedules which will give the optimal mutation yield. Previous work with short term DBE exposures of clone 4430 has been extended in the present study up to 144 h at appropriate concentrations varying from 1 to 100 ppm. The resulting data on pink-celled stamen hair m u t a t i o n frequencies are expressed as mean values for the peak response period (6--10 days after exposure). Concentration (C)-response curves for each exposure period used show straight line relationships on log/log plots with slopes approaching 2. Since these data show a consistent increase in sensitivity with increasing time (T) of exposure the log/log plot of m u t a t i o n response vs T X C also exhibit a straightline relationship but with a 1.11 slope (Corr. coef. = 0.94). The mutation response frequency following the 144-h (6-day) exposure at 2 ppm of DBE was 5 events per 100 stamen hairs or equivalent to that produced by about 50 rad of X rays. Since previous experiments with clone 4430 have established statistically significant increases in m u t a t i o n rates of 0.5 per 100 hairs for DBE and 0.1 for X rays, meaningful data should be obtainable at DBE levels as low as 0.1 ppm based on extrapolations of the 144-h concentration-response and T X C curves. The sensitivity of the Tradescantia test system in this range should make it adaptable to mutagen monitoring at very low levels of
406 known or suspected mutagenic air pollutants. R e s e a r c h s u p p o r t e d in p a r t b y t h e U.S. E n e r g y R e s e a r c h and D e v e l o p m e n t A d m i n i s t r a t i o n and in p a r t b y the N a t i o n a l I n s t i t u t e of E n v i r o n m e n t a l H e a l t h S c i e n c e s .
57 C.H. Nauman, P.J. Klotz and A.H. Sparrow, Biology and Applied Science Departments, Brookhaven National Laboratory, Upton, New York 11973 (U.S.A.)
Dosimetry of tritiated 1,2-dibromoethane in floral tissues of Tradescantia Inflorescences of Tradescantia clone 4430, heterozygous for flower color, were exposed to various concentrations of gaseous tritiated 1,2-dibromoethane ([3H]DBE). The pink somatic mutation dose-response curve from a series of experiments was parallel to that determined previously for non-labeled DBE, b u t elevated due to the contribution of the beta radiation. Floral parts were dissected from buds following exposures of from 15 min to 6 h and analyzed for tissue concentration of [3H]DBE by liquid scintillation counting. The bud tissue concentration of [3H]DBE increased in proportion to the exposure concentration. Sepal, petal, anther, stamen and ovary tissues contained similar amounts of activity per mg, indicating that penetration of the chemical was uniform. Subsequent experiments, only partially analyzed at present, indicate that penetration of the gaseous DBE to inner tissues is rapid. Tissues from flowers which opened for up to 10 days after exposure retained only slightly declining amounts of radioactivity, indicating that the [3H]DBE or 3H is tightly b o u n d in the tissues. Autoradiographs of stamen hair tissue from buds show silver grains that are randomly distributed over the nucleus and cytoplasm immediately after exposure and for up to 12 days later. Thus, [3H]DBE is n o t localized within the cell. R e s e a r c h s u p p o r t e d in p a r t b y t h e U.S. E n e r g y R e s e a r c h and D e v e l o p m e n t A d m i n i s t r a t i o n and in p a r t b y t h e N a t i o n a l I n s t i t u t e of E n v i r o n m e n t a l H e a l t h S c i e n c e s .
58 S. Mittler, Northern Illinois University, DeKalb, Illinois 60115 (U.S.A.) Screening for induced chromosome loss and non-disjunction in Drosophila melanogaster Adult Drosophila males yB/scSy ÷are either injected, fed or exposed to the suspected mutagen and then mated every two days to ywf. The appearance of ywf male, the XO male was a result of a loss of X or Y chromosomes, and the exceptional wild body Bar eye female, XXY indicated a primary non-disjunction event. The brooding m e t h o d was used to assess the sensitivity of the various stages of spermatogenesis to the possible mutagen. Digitonin, a microtubule