unique program for cell death in xylem fibers of Populus stem

• Published in: The Plant journal : for cell and molecular biology Vol. 58; no. 2; pp. 260 - 274
• Main Authors: Courtois-Moreau, Charleen L, Pesquet, Edouard, Sjödin, Andreas, Muñiz, Luis, Bollhöner, Benjamin, Kaneda, Minako, Samuels, Lacey, Jansson, Stefan, Tuominen, Hannele
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01-04-2009; Blackwell Publishing Ltd; Blackwell
• Subjects: Ageing, cell death; apoptosis; autophagy; Biological and medical sciences; Botany; Cell Death; Cell physiology; Cell Wall - metabolism; Cellular biology; Comet Assay; Deoxyribonucleic acid; DNA; DNA degradation; DNA, Plant - analysis; Electron microscopes; Fibers; Fundamental and applied biological sciences. Psychology; Gene Expression Profiling; Gene Expression Regulation, Plant; General aspects; in silico transcriptional analysis; In Situ Nick-End Labeling; Mathematics in biology. Statistical analysis. Models. Metrology. Data processing in biology (general aspects); Microarray Analysis; Microscopy, Electron, Transmission; Molecular and cellular biology; Plant Stems - cytology; Plant Stems - genetics; Plant Stems - metabolism; Populus; Populus - genetics; Populus - metabolism; programmed cell death; Vacuoles - metabolism; Xylem - metabolism; xylem fiber development; Xylem; Transcription; Autophagy; Stem; Salicaceae; Degradation; Cell death; Dicotyledones; DNA; Angiospermae; Development; Spermatophyta; Populus; DNA degradation; programmed cell death; xylem fiber development; Bioinformatics; Apoptosis; in silico transcriptional analysis
• ISSN: 0960-7412; 1365-313X; 1365-313X
• DOI: 10.1111/j.1365-313x.2008.03777.x

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.