Programmed cell death is an integral part of the latest stage of differentiation of the tracheary elements of plant xylem vascular system. In this study, by applying a pharmacological approach with specific peptide inhibitors, we have elucidated the involvement of plant caspase-like proteases in cell death signaling during vessel elements formation in xylogenic zinnia (Zinnia elegans) cell culture. Cell culture was isolated from zinnia leaves and exposed to chemical treatments. Broad spectrum caspase inhibitor, caspase 1 and caspase-3 inhibitors were administrated to the cell culture where the cells were induced to differentiate with the addition of 1 mg/L benzylaminopurine and 0.1 mg/L ¿-naphthalene-acetic acid. The differentiation was substantially suppressed in presence of 100 nM concentration of the inhibitors. This indicates that the re-differentiation in cultured mesophyll zinnia cells is a PCD event that most probably occurs through signaling involving caspase-like proteases. The reported results are the first that provide evidence for participation of plant caspase-related enzymes in xylogenesis in zinnia. Laser scanning confocal microscopy revealed differentiation associated structural cellular changes, including formation of large vacuole, secondary wall thickenings, tonoplast rupture and cell autolysis to form hollow dead tracheary elements..