Effect of caffeine and adenosine on G2 repair: mitotic delay and chromosome damage

Proliferating plant cells treated during the late S period with 5-aminouracil (AU), give the typical response that DNA-damaging agents induce, characterized by: an important mitotic delay, and a potentiation of the chromosome damage by caffeine post-treatment. The study of labelled prophases, after a tritiated thymidine pulse, allowed evaluation of the mitotic delay induced by AU as well as its reversion by caffeine, while chromosome damage was estimated by the percentage of anaphases and telophases showing chromosomal aberrations. Post-treatment with adenosine alone has shown no effect on mitotic delay or chromosomal damage. However, when cells after AU were incubated in caffeine plus adenosine, the chromosome damage potentiation was abolished without affecting the caffeine action on mitotic delay. As a consequence, we postulate that caffeine could have two effects on G2 cells with damaged DNA: the first, to cancel their mitotic delay and the second to inhibit some DNA-repair pathway(s). Only this last effect could be reversed by adenosine.