DNA fragmentation in cereal roots indicative of programmed root cortical cell death

In cereals, a progressively increasing root cortical cell death (RCD) occur s from the root tip and upwards when measured with vital staining methods. In this study, nuclear DNA fragmentation was studied in seminal root segmen ts of wheat and barley in order to investigate if the cell death resembled apoptosis, The fraction of cells with TUNEL-positive nuclei increased gradu ally with increasing root age in both the cortex and the stele, Southern an alysis showed a typical ladder pattern, indicating nucleosomal fragmentatio n already in 2-day-old root segments, and this became more pronounced in ol der root segments, DNA fragmentation appeared to be more extensive in wheat than in barley roots. These results confirm earlier studies, where RCD has been found to be earlier initiated and to proceed at a faster rate in whea t. The characteristic DNA fragmentation found in the roots indicates progra mmed cell death with mechanistic similarities to apoptosis, Ultrastructural examination of nuclei in cortex cells with transmission electron microscop y revealed an increased chromatin condensation in older roots, particularly in wheat, In addition, we found nucleosomal DNA ladders in young leaf tissue from whe at but not from barley.