Caspase inhibitors affect the kinetics and dimensions of tracheary elements in xylogenic Zinnia (Zinnia elegans) cell cultures

Confocal microscopic images revealed the consecutive stages of TE formation in Zinnia cells during trans-differentiation. Application of the caspase inhibitors Z-Asp-CH2-DCB, Ac-YVAD-CMK and Ac-DEVD-CHO affected the kinetics of formation and the dimensions of the TEs resulting in a significant delay of TE formation, production of larger TEs and in elimination of the 'two-wave' pattern of TE production. DNA breakdown and appearance of TUNEL-positive nuclei was observed in xylogenic cultures and this was suppressed in the presence of caspase inhibitors.To the best of our knowledge this is the first report showing that caspase inhibitors can modulate the process of trans-differentiation in Zinnia xylogenic cell cultures. As caspase inhibitors are closely associated with cell death inhibition in a variety of plant systems, this suggests that the altered TE formation results from suppression of PCD. The findings presented here are a first step towards the use of appropriate PCD signalling modulators or related molecular genetic strategies to improve the hydraulic properties of xylem vessels in favour of the quality and shelf life of plants or plant parts.Maintenance and structuring of tissues and organs, homeostasis and defence in biological organisms are controlled by well coordinated and active cellular processes of death and survival. Programmed cell death (PCD) is a cell suicide genetically programmed, developmentally associated and environmentally stimulated mechanism and has been found throughout animal and plant kingdoms [1-6]. PCD is aimed at establishing functional structures, at removal of cells that are harmful or no longer needed, and it plays a prominent role in resistance and adaptation to abiotic and biotic insults. In mammalian cells, a type of PCD commonly referred to as apoptosis, is mediated by cysteinyl-aspartic proteases (caspases), involving initiator caspases and downstream executioner caspases. This results in a typical phenotype comprised of cell