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Tyloses and phenolic deposits in xylem vessels impede water transport in low-lignin transgenic poplars: a study by cryo-fluorescence microscopyAuthor(s): Peter Kitin; Steven L. Voelker; Frederick C. Meinzer; Hans Beekman; Steven H. Strauss; Barbara Lachenbruch
Source: Plant Physiology. 154: 887-898
Publication Series: Scientific Journal (JRNL)
Station: Pacific Northwest Research Station
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DescriptionOf 14 transgenic poplar genotypes (Populus tremula x Populus alba) with antisense 4-coumarate:coenzynle A ligase that were grown in the field for 2 years, five that had substantial lignin reductions also had greatly reduced xylem-specific conductivity compared with that of control trees and those transgenic events with small reductions in lignin. For the two events with the lowest xylem lignin contents (greater than 40% reduction), we used light microscopy methods and acid fuchsin dye ascent studies to clarify what caused their reduced transport efficiency. A novel protocol involving dye stabilization and cryo-fluorescence microscopy enabled us to visualize the dye at the cellular level and to identify water-conducting pathways in the xylem. Cryo-fixed branch segments were planed in the frozen state on a sliding cryo-microtome and observed with an epifluorescence microscope equipped with a cryo-stage. We could then distinguish clearly between phenolic-occluded vessels, conductive (stain-filled) vessels, and nonconductive (water- or gas-filled) vessels. Low-lignin trees contained areas of nonconductive, brown xylem with patches of collapsed cells and patches of noncollapsed cells filled with phenolics. In contrast, phenolics and nonconductive vessels were rarely observed in normal colored wood of the low-lignin events. The results of cryo-fluorescence light microscopy were supported by observations with a confocal microscope after freeze drying of cryo-planed samples. Moreover, after extraction of the phenolics, confocal microscopy revealed that many of the vessels in the nonconductive xylem were blocked with tyloses. We conclude that reduced transport efficiency of the transgenic low-lignin xylem was largely caused by blockages from tyloses and phenolic deposits within vessels rather than by xylem collapse.
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CitationKitin, Peter; Voelker, Steven L.; Meinzer, Frederick C.; Beekman, Hans; Strauss, Steven H.; Lachenbruch, Barbara. 2010. Tyloses and phenolic deposits in xylem vessels impede water transport in low-lignin transgenic poplars: a study by cryo-fluorescence microscopy. Plant Physiology. 154: 887-898.
Keywordshybrid poplar, reduced lignin, xylem vessel, phenolic deposition, tyloses
- Antisense down-regulation of 4CL expression alters lignification, tree growth, and saccharification potential of field-grown poplar
- Transgenic poplars with reduced lignin show impaired xylem conductivity, growth efficiency and survival
- Reduced wood stiffness and strength, and altered stem form, in young antisense 4CL transgenic poplars with reduced lignin contents
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