Sister-chromatid exchange formation at supra-optimal growth temperatures

The present research was mainly focused on characterizing the formation of sister-chromatid exchanges at both optimal and supra-optimal growth temperatures. Under these conditions (25, 30 and 35 degrees C) meristem cells of Allium cepa L. exhibited a roughly constant cell-cycle time, and modifications in other cell-cycle parameters were negligible. Second-division chromosomes of cells incubated at 30 and 35 degrees C showed increased SCE yields as compared with those detected in cells maintained at the optimal temperature (25 degrees C). When cells with unifilarly BrdUrd-substituted DNA was damaged by irradiation with visible light, we obtained almost the same SCE yields at the various temperatures tested. We suggest that this production of SCEs could be the result of a reduced number of lesions produced by light (perhaps as a consequence of reduced intracellular free oxygen at high temperature) and/or of an increased efficiency in the repair capacity of the cells at these temperatures. The analysis of SCE formation in undamaged cells incubated at different temperatures during BrdUrd treatment has shown that the optimal growth temperature appears to be the experimental condition in which the cells are able to exhibit the lowest frequency of SCE.