title: Caspase inhibitors affect the kinetics and dimensions of tracheary elements in xylogenic Zinnia (Zinnia elegans) cell cultures.
abstract: BACKGROUND
  The xylem vascular system is composed of fused dead, hollow cells called tracheary elements (TEs) that originate through trans-differentiation of root and shoot cambium cells. TEs undergo autolysis as they differentiate and mature. The final stage of the formation of TEs in plants is the death of the involved cells, a process showing some similarities to programmed cell death (PCD) in animal systems. Plant proteases with functional similarity to proteases involved in mammalian apoptotic cell death (caspases) are suggested as an integral part of the core mechanism of most PCD responses in plants, but participation of plant caspase-like proteases in TE PCD has not yet been documented.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Wageningen University, Plant Sciences Group, Horticultural Supply Chains, 6700 AP Wageningen, The Netherlands.
authors.forename: Peter
authors.initials: P
authors.lastname: Twumasi
authors.forename: Elena T
authors.initials: ET
authors.lastname: Iakimova
authors.forename: Tian
authors.initials: T
authors.lastname: Qian
authors.forename: Wim
authors.initials: W
authors.lastname: van Ieperen
authors.forename: Jan H N
authors.initials: JH
authors.lastname: Schel
authors.forename: Anne Mie C
authors.initials: AM
authors.lastname: Emons
authors.forename: Olaf
authors.initials: O
authors.lastname: van Kooten
authors.forename: Ernst J
authors.initials: EJ
authors.lastname: Woltering
mesh_terms: D019659:Asteraceae / Q000166:cytology* / Q000187:drug effects*; D018929:Cell Culture Techniques; D002454:Cell Differentiation / Q000187:drug effects*; D053938:DNA Fragmentation / Q000187:drug effects; D004791:Enzyme Inhibitors; D052584:Xylem / Q000166:cytology* / Q000187:drug effects*
chemical_list: D004791:Enzyme Inhibitors