title: A unique program for cell death in xylem fibers of Populus stem.
abstract: Maturation of the xylem elements involves extensive deposition of secondary cell-wall material and autolytic processes resulting in cell death. We describe here a unique type of cell-death program in xylem fibers of hybrid aspen (Populus tremula x P. tremuloides) stems, including gradual degradative processes in both the nucleus and cytoplasm concurrently with the phase of active cell-wall deposition. Nuclear DNA integrity, as determined by TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling) and Comet (single-cell gel electrophoresis) assays, was compromised early during fiber maturation. In addition, degradation of the cytoplasmic contents, as detected by electron microscopy of samples fixed by high-pressure freezing/freeze substitution (HPF-FS), was gradual and resulted in complete loss of the cytoplasmic contents well before the loss of vacuolar integrity, which is considered to be the moment of death. This type of cell death differs significantly from that seen in xylem vessels. The loss of vacuolar integrity, which is thought to initiate cell degradative processes in the xylem vessels, is one of the last processes to occur before the final autolysis of the remaining cell contents in xylem fibers. High-resolution microarray analysis in the vascular tissues of Populus stem, combined with in silico analysis of publicly available data repositories, suggests the involvement of several previously uncharacterized transcription factors, ethylene, sphingolipids and light signaling as well as autophagy in the control of fiber cell death.
authors.affiliation: Umeå Plant Science Centre, Department of Plant Physiology, Umeå University, 90187 Umeå, Sweden.
authors.forename: Charleen L
authors.initials: CL
authors.lastname: Courtois-Moreau
authors.forename: Edouard
authors.initials: E
authors.lastname: Pesquet
authors.forename: Andreas
authors.initials: A
authors.lastname: Sjödin
authors.forename: Luis
authors.initials: L
authors.lastname: Muñiz
authors.forename: Benjamin
authors.initials: B
authors.lastname: Bollhöner
authors.forename: Minako
authors.initials: M
authors.lastname: Kaneda
authors.forename: Lacey
authors.initials: L
authors.lastname: Samuels
authors.forename: Stefan
authors.initials: S
authors.lastname: Jansson
authors.forename: Hannele
authors.initials: H
authors.lastname: Tuominen
mesh_terms: D016923:Cell Death; D002473:Cell Wall / Q000378:metabolism; D020552:Comet Assay; D018744:DNA, Plant / Q000032:analysis; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D020287:In Situ Nick-End Labeling; D046228:Microarray Analysis; D046529:Microscopy, Electron, Transmission; D018547:Plant Stems / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D032107:Populus / Q000235:genetics / Q000378:metabolism*; D014617:Vacuoles / Q000378:metabolism; D052584:Xylem / Q000378:metabolism*
chemical_list: D018744:DNA, Plant