Caffeine, caffeine derivatives and chromosomal aberrations

摘要

The frequencies of “sub-chromatid” and chromatid exchanges produced in root tips of Vicia faba by 8-methoxycaffeine (MOC), 8-ethoxycaffeine (EOC), and 1,3,7,9-tetramethyluric acid (TMU) are characteristically influenced by the concentration of these N-methylated oxypurines and by the temperature during treatment. For studies on the relationship between concentration and effect, roots were exposed to EOC for 1 hour at 15°C. No aberrations were produced when the EOC concentration was 2 × 10-3M or lower. With 6 × 10-3M EOC 20 aberrations per 100 cells were obtained, with 8 × 10-3M 87 and with 10-2M 150. Thus, once the threshold concentration for the chromosome-breaking effect was reached, a doubling of the concentration resulted in a five- to tenfold increase of the aberration frequency. When treatments were carried out at different temperatures, the maximum effect was obtained between 10 and 15°C with MOC and EOC and between 15 and 20°C with TMU. At temperatures above 25°C, very few aberrations were produced with MOC and EOC. When the first 1/2 hour of a 1-hour treatment was carried out at 10°C and the second 1/2 hour at 30°C, the effect obtained was less than 1/3 of that produced when the temperature was 10°C during the whole 1-hour treatment or 30°C during the first and 10°C during the second 1/2 hour. The results are discussed and a mechanism is proposed for the production of chromosomal exchanges by N-methylated oxypurines.