Nuclear and Cell Division in Allium cepa as Influenced by Slow Neutrons and X-Rays

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Abstract
Bulbs of A. cepa, var. Ebenezer, were exposed to X-ray dosages of 100 r, 1000 r, and 10,000 r, or to slow neutrons produced in the Argonne heavy water pile. The neutron-treated material was exposed to an avg. neutron flux of 5.8 x 1010 slow neutrons/sq. cm./sec. for periods of 2, 4, 8, or 16 min. Cytological analysis of root tips collected at 48-, 52-, and 96-hr. intervals showed that the effects of both types of treatment followed a pattern that was chronologically detd: a general, but temporary, inhibition of mitosis; abnormal nuclear division necessitated by structural chromosome aberrations; abnormal cell division directly following aberrant nuclear division; and lastly, degeneration of nuclei and cells which had been severely damaged either by the original treatment or by disorientation in normal cell processes during the preceding stages. Chromosomal aberrations of all types[long dash]dicentrics, centric and centric ring, acentric fragments, and dot deletions[long dash]were observed in root-tip cells from both treatments. The marked inhibition of mitosis found and the low dosage-curve exponents obtained for aberration frequency indicate that with regard to quantitative detn. of the relationship between excessive treatment with slow neutrons and response of the organism, aberration frequency alone does not yield a wholly representative or valid index of the true picture of dosage effect.