An investigation of LET 'finger-prints' in Tradescantia

Chromosome-type aberration scores, obtained in the Tradescantia microspore system following exposure to radiation, have been extracted from all significant papers since 1940, and augmented with unpublished results from this laboratory. The data include aberrations produced by X-, gamma-rays and neutrons, and cover an enormous range of qualities, doses, dose-rates and ambient gas conditions. Two proposed LET 'finger-print' ratios were examined: Dicentrics/Centric-rings (D/R or F-ratio) and Total deletions/Dicentrics+Centric-rings. There was no significant effect of LET on either of these. Further, D/R was independent of dose, whereas Deletions/D+R showed, as expected, a positive dose effect. In a very small subset of experiments, sizes of interstitial deletions had been recorded, and a significant reduction in modal size was observed for neutrons compared to X-rays. Even if this observation is confirmed by future work, it will not provide a usable 'finger-print' for long-term studies since, being acentric, deletions are rapidly eliminated from a dividing cell population.