The Structural Chromosome Aberrations Produced By 5-Aminouracil and Their Prevention by an Additional Thymine Source

抄録

When roots of Vicia faba are immersed in a solution of a thymine analogue, 5-aminourcil, 50 ppm. chromosome aberrations are induced at anaphase. Among these are chromosomes which are bent so that a polar group has a bell-shaped outline, chromosomes which disjoin faultily and chromosomes which contain with increased frequency regions devoid of material stainable with the Feulgen procedure.
Sites of differential response (Feulgen-negative regions in the terminology of Duncan and Woods) have recognizable locations. They lie in or near regions which other authors have identified as heterochromatin. The frequency with which these sites become Feulgen-negative is highest in roots treated with 5-aminouracil for 12 hours, lower in roots treated for 24 hours and lowest in control roots and roots which are recovering in distilled water 24-48 hours after removal from a 24 hour treatment with 5-aminouracil. The change in frequency from 12 to 24 hour treatments constitutes a partial recovery.
In roots treated with a mixture of 5-aminouracil 50 ppm. and cytidine sulfate 126 ppm. the frequency is intermediate between that of control roots and of roots treated with 5-aminouracil alone. The Feulgen-negative regions, therefore, are considered segments of chromosomes where interference in pyrimidine metabolism is critical, an exogenous source antagonizing the antimetabolite 5-aminouracil. Other aberrancies induced by treatment with 5-aminouracil are less intense.
Since comparable sites of sister chromosomes at anaphase are often similary affected and since Feulgen-negative regions can be demonstrated in metaphase chromosomes, a preanaphase cause is indicated. Their incidence in roots treated with 5-aminouracil is highest when the mitotic index is lowest, a fact associating their origin with inhibition of DNA synthesis. DNA synthesis, of course, occurs during interphase. Perhaps initiation of Feulgennegative regions is an aspect of its interference in DNA metabolism.