Apoptosis detected in hybrids between Nicotiana glutinosa and N-repanda expressing lethality

Hybrid lethality is one of the mechanisms for reproductive isolation. Apopt otic features were detected in the cells of hybrid seedlings of Nicotiana g lutinosa L. x N. repanda Willd. Condensation of chromatin and fragmentation of nuclei were observed in the leaf protoplasts isolated from hybrid seedl ings expressing this lethality. Fragmentation of nuclei was correlated with the progression of lethal symptoms, as confirmed by fluorimetry of the nuc lear DNA using laser scanning cytometry. Agarose gel analysis of DNA extrac ted from hybrid leaves showing lethality revealed a specific ladder pattern suggesting nucleosomal fragmentation associated with nuclear fragmentation . In-situ detection of DNA fragmentation using terminal deoxyribonucleotidy l transferase-mediated dUTP-fluorescein nick end labeling (TUNEL) showed th at this process occurred in all leaf cells. This is the first evidence that apoptosis can induce suicide of hybrid plants, thus leading to reproductiv e isolation.