The Effect of Thermal Neutron Radiation on the Chromosomes of Datura

Abstract

Seeds of D. stramonium, Line l,were exposed to radiation in the thermal neutron column at the nuclear reactor for 2 hrs. at a flux of approx. 4.6 x 108Nth/cm2/sec. (cadmium ratio about 5000; 1 and gamma contamination about 50r/hr.). Seeds were germinated in the greenhouse, then transplanted to the field. After mature plants had been studied for sectors of good and bad pollen, aceto-carmine-smear prepns. were made from anthers of both good and bad sectors for detection of translocations. Pollen was classified on the basis of chromosomal type (empty, shriveled) and gene type (very small with degenerate contents). Comparisons between the 2 types indicated a statistically significant difference with respect to proportion of chromosomal aberrations, in most cases the chromosomal type being correlated with translocations and the gene type with 12 bivalents. Of 55 plants having 10% or less pollen abortion all but 2 had normal chromosomes with respect to interchanges. 26 of the 32 plants having more than 10% pollen abortion had the chromosomal type, indicating a preponderance of chromosomal changes. Since, however, most of the plants showing translocations had 50% bad pollen, and it is known that translocations in Datura give good pollen or 25% bad pollen, it is likely that genic changes occurred frequently along with chromosomal changes. It is also possible that thermal neutrons may induce a more complex pattern of aberrations than other agents, giving a higher percentage of pollen abortion. Two plants were found to have an extra bivalent in a limited sector with no visible morphological effects. In both cases the cells involved were highly aberrant, and it is suggested that a delayed effect of the neutron radiation may have produced the localized effect.