CHROMOSOME BREAKAGE INDUCED IN VICIA FABA ROOT TIPS BY 2,4,6-TRI(ETHYLENEIMINO)-1,3,5-TRIAZINE

Abstract

After a 12-hour treatment in 10⁻⁵ M solution of 2,4,6-tri(ethyleneimino)-1,3,5-triazine (TEM), up to 29% of Vicia and 31% of Allium root cells in anaphase had bridges or fragments. The most abundant metaphase aberrations were chromosome breaks and chromatid interchanges. Aberrations were more numerous after 6-hour treatment with 2 × 10⁻⁵ M than after 12-hour treatment with 10⁻⁵ M solution. The peak aberration frequencies were reached at 36 hours after 2 × 10⁻⁵ M treatments and slightly earlier with weaker solutions. Many chromosomes had incomplete breaks. Sister reunions of chromatids occurred with equal frequency in centric and acentric fragments. Sister reunion was 1.5 times as frequent as chromatid exchange. Along the length of the satellite chromosome, breaks occurred at random except for a slight favoring of the heterochromatic region. Per unit of length the short chromosomes were about 3 times as susceptible to breakage and exchange as satellite chromosomes. TEM introduced through cut stems had no discernible effects on Tradescantia microspore chromosomes even after 3 to 5 days of treatment.