AbstractProgrammed Cell Death (PCD) is an essential process utilised for the defence and development of all multicellular organisms. In plants however, relatively little is known about the genes involved with the regulation and execution of this process. In particular, even less is known about the molecular components which act high up in the PCD pathway. In this thesis, we carried out an investigation into the novel peptide-encoding gene KISS OF DEATH (KOD). In Arabidopsis, KOD was found to be involved with mediating the elimination of the suspensor, an organ which undergoes developmental PCD. Two mutant alleles of KOD showed reduced PCD in both the suspensor and during heat-shock induced PCD of root hairs. Over-expression of KOD in plant tissues was sufficient to cause death in leaves or whole seedlings and involved the activation of caspase-like proteolytic activity. KOD-induced PCD was found to require light in leaves and is also sensitive to the PCD suppressor genes AtBI-1 and P35. We suggest that KOD acts high up in the PCD cascade as its expression resulted in depolarisation of the mitochondrial membrane, which is an early step in plant PCD. KOD appears to be a plant-specific peptide that is sufficient to induce PCD in Arabidopsis in the absence of external triggers. Typical BLAST searches yielded no obvious homolog for KOD, therefore a bioinformatics screen of the Arabidopsis genome was carried out. This screen for small genes similar in size to KOD enabled us to detect 10 previously unidentified genes, one of which may represent a putative KOD homolog. In summary, KOD appears to be a novel pro-PCD component of the Arabidopsis cell death machinery and represents the first plant peptide to be involved with a form of developmental PCD.