SEASONAL VARIATION OF X-RAY-INDUCED CHROMATID ABERRATION FREQUENCIES IN CULTURED POLLEN TUBES OF Tradescantia

Resumen

Cultured pollen tubes of Tradescantia were X-irradiated (310 R) during mitosis of the generative nucleus. For experiments conducted intermittently through the seasons of the year, X-irradiation was applied at interphase (G₂), 5-7 min after sowing the pollen grains on the medium. For experiments conducted only in summer and designed to treat prophase and metaphase chromosomes, X-irradiation was applied 8 hr and 18 hr, respectively, after sowing. Treated and control cultures were fixed after 18 hr of growth for scoring chromatid aberrations in
metaphase figures. Results from year round studies showed seasonal variation of aberration frequencies similar to those observed in hydroxyurea and SO₂ studies previously reported. The average aberration frequency, expressed in terms of aberrations per 100 cells, was 140 in summer, 95 in fall, 48 in winter and 19
in spring. Cultures treated at later stages of mitosis in summer showed 38 aberrations per 100 cells in prophase and 11 in metaphase, while the controls for ali experiments has around 5. The discrepencies between seasons and between stages of mitosis could be interpreted as an implication of changing frequencies of sister chromatid crossingover, a spontaneous process of breakage and fusion of chromatids. Results of a comparative analysis of the seasonal changes of mutagenic efficiencies of X-rays of present study with those of hydroxyurea and 10₂ of previous studies further substantiate the concepto proposed.