Unscheduled apoptosis in meristematic plant cells is triggered via terminal deletions in artificially elongated chromosome arms

 Chromosomes elongated beyond a critical size by balanced rearrangements reduce the viability and fertility of field bean individuals. The severity of symptoms, ranging from growth retardation to early death of seedlings, increases with the length of the longest chromosome arm. This is paralleled by the incomplete separation of sister chromatids during nuclear division, resulting in chromatin connections between daughter nuclei which become disrupted by cell-wall formation and yield chromatid deletions detectable as micronuclei. By means of the TUNEL assay we show that, compared to the wild-type, a >6-fold higher number of meristematic cells of karyotypes with chromosome arms surpassing the limit of tolerance reveal apoptotic nuclei and are prone to die. Thus, terminal chromatid deletions apparently trigger unscheduled apoptosis. Extensive cell death in meristems is eventually responsible for reduced growth, disturbed development and reduced seed set. Differentiated root tissues and microspores did not reveal apoptotic nuclei. Received: 20 November 1997 / Accepted: 9 December 1997