Inhibition of cell growth in roots of Allium cepa by caffeine and isobutylmethylxanthine

Abstract

Roots of Allium cepa were treated for 1 hr with 0.1% solutions of caffeine or isobutylmethylxanthine (IBMX). Both compounds induce the formation of binucleate cells. Both compounds also inhibit growth of: (1) cells proceeding into mitosis during treatment; (2) late G 2-prophase nuclie. This response was found in random samples of cells and confirmed by studies of pairs of sister cells, one of which was in mitosis and one of which was in G 2. The results showed a marked inhibition of growth at the end of G 2 and during mitosis. The binucleate cells induced by treatment were studied over 1 cell cycle. The two sister nuclei were not identical in volume when first formed and the difference was subsequently maintained throughout interphase. The binucleate cells with the shortest cell cycle were in division 18 hr after treatment. Their mean cell area showed only a 1.58-fold increase over mean area in very early G 1, i.e. they did not double in area over a cell cycle. Diploid, mononucleate cells in division 18 hr after treatment, i.e. in division at the same time as binucleate cells, were significantly smaller than mitotic cells of untreated roots. This suggests that the response of these cells to treatment with methylxanthines is similar to that of binucleate cells. Mononucleate cells in mitosis at 1 + 18 hr had undergone only a 1.4-fold increase in cell area; this is much less than the doubling in mean cell area seen in untreated cells over one cycle. It appears that profound disturbances of cell and nuclear growth are induced in A. cepa by even a 1 hr treatment with caffeine or IBMX.