UV-B overexposure induces programmed cell death in a BY-2 tobacco cell line

There is not a great deal of information available on the effects of overexposure of ultraviolet B (UV-B) on programmed plant cell death in cell cultures. Applying fluorescent microscopy, typical apoptotic morphological features such as cell shrinkage, condensation of chromatin in perinuclear areas and formation of micronuclei were all observed in UV-B treated BY-2 tobacco cells. Moreover, cell acidification as an apoptosis-related process was also detected in irradiated cells. Because of the wide variety of morphological changes that have been associated with UV-B-caused cell apoptosis, it is difficult to attribute any of these changes to a particular molecular mechanism. DNA laddering and TUNEL assays also indicated a dose-dependent specific nucleosomal DNA fragmentation under ultraviolet irradiation. These observations clearly indicate that UV-B irradiation can initiate apoptotic processes in plant cells.