Intrusive growth of sclerenchyma fibers

Intrusive growth is a type of cell elongation when the rate of its longitudinal growth is higher than that of surrounding cells; therefore, these cells intrude between the neighboring cells penetrating the middle lamella. The review considers the classical example of intrusive growth, e.g., elongation of sclerenchyma fibers when the cells achieve the length of several centimeters. We sum the published results of investigations of plant fiber intrusive growth and present some features of intrusive growth characterized by the authors for flax (Linum usitatissimum L.) and hemp (Cannabis sativa L.) fibers. The following characteristics of intrusive growth are considered: its rate and duration, relationship with the growth rate of surrounding cells, the type of cell elongation, peculiarities of the fiber primary cell wall structure, fibers as multinucleate cells, and also the control of intrusive growth. Genes, which expression is sharply reduced at suppression of intrusive growth, are also considered. Arguments for separation of cell elongation and secondary cell wall formation in phloem fibers and also data indicating diffuse type of cell enlargement during intrusive growth are presented

Intrusive growth of flax phloem fibers is of intercalary type

Flax (Linum usitatissimum L.) phloem fibers elongate considerably during their development and intrude between existing cells. We questioned whether fiber elongation is caused by cell tip growth or intercalary growth. Cells with tip growth are characterized by having two specific zones of cytoplasm in the cell tip, one with vesicles and no large organelles at the very tip and one with various organelles amongst others longitudinally arranged cortical microtubules in the subapex. Such zones were not observed in elongating flax fibers. Instead, organelles moved into the very tip region, and cortical microtubules showed transversal and helical configurations as known for cells growing in intercalary way. In addition, pulse-chase experiments with Calcofluor White resulted in a spotted fluorescence in the cell wall all over the length of the fiber. Therefore, it is concluded that fiber elongation is not achieved by tip growth but by intercalary growth. The intrusively growing fiber is a coenocytic cell that has no plasmodesmata, making the fibers a symplastically isolated domain within the stem

MALDI-TOF MS evidence for the linking of flax bast fibre galactan to rhamnogalacturonan backbone

Fibre-specific (1 ¿ 4)-ß-galactan extracted from bast fibre peels of developing flax (Linum usitatissimum L.) stem has been studied to elucidate its structural details. The polysaccharide was characterized by NMR and subjected to partial degradation protocols, including chemical and enzymatic approaches. The oligosaccharide fragments obtained were fractionated by gel permeation chromatography and analyzed for their molecular mass with MALDI-TOF MS. The obtained data show that this flax galactan is a complex RG-I polysaccharide with variable side chain structures. The backbone is composed of the common GalA-Rha repeats with a high degree of branching. These side chains are mainly composed of ß-1,4-linked Gal oligomers: (1) short branches of only one or two Gal residue(s); (2) long (linear) branches of up to 26 Gal residues; (3) mixed branches of between 3 and 12 Gal residues (possibly derived from longer linear side chains), that are resistant to galactanase cleavage; (4) side chains of at least 17 Gal residues, decorated with single Ara moieties. The linkage between RG backbone and galactan side chains was confirmed by the presence of fragments with (Rha-GalA)nHexm structure type. Neither chemical, nor enzymatic hydrolysis yielded oligomeric GalA residues, indicating that RG-I blocks are not interrupted by HGA regions. The polymer can be cleaved only partially by the rhamnogalacturonan hydrolase used, while the remaining part is resistant, probably due to peculiarities of side chain structure. Novel Rha-GalA oligomers were liberated by RG-hydrolase containing two or three Gal attached to Rha near the cleavage site. The native polymer is decorated by acetyl groups, with yet unknown distribution patterns. Treatment with purified and well-characterized galactanase does not change the hydrodynamic volume of flax galactan (despite considerable cleavage of Gal moieties), suggesting a complex ¿secondary¿ structure of the polymer

MALDI-TOF MS evidence for the linking of flax bast fibre galactan to rhamnogalacturonan backbone

Fibre-specific (1 ¿ 4)-ß-galactan extracted from bast fibre peels of developing flax (Linum usitatissimum L.) stem has been studied to elucidate its structural details. The polysaccharide was characterized by NMR and subjected to partial degradation protocols, including chemical and enzymatic approaches. The oligosaccharide fragments obtained were fractionated by gel permeation chromatography and analyzed for their molecular mass with MALDI-TOF MS. The obtained data show that this flax galactan is a complex RG-I polysaccharide with variable side chain structures. The backbone is composed of the common GalA-Rha repeats with a high degree of branching. These side chains are mainly composed of ß-1,4-linked Gal oligomers: (1) short branches of only one or two Gal residue(s); (2) long (linear) branches of up to 26 Gal residues; (3) mixed branches of between 3 and 12 Gal residues (possibly derived from longer linear side chains), that are resistant to galactanase cleavage; (4) side chains of at least 17 Gal residues, decorated with single Ara moieties. The linkage between RG backbone and galactan side chains was confirmed by the presence of fragments with (Rha-GalA)nHexm structure type. Neither chemical, nor enzymatic hydrolysis yielded oligomeric GalA residues, indicating that RG-I blocks are not interrupted by HGA regions. The polymer can be cleaved only partially by the rhamnogalacturonan hydrolase used, while the remaining part is resistant, probably due to peculiarities of side chain structure. Novel Rha-GalA oligomers were liberated by RG-hydrolase containing two or three Gal attached to Rha near the cleavage site. The native polymer is decorated by acetyl groups, with yet unknown distribution patterns. Treatment with purified and well-characterized galactanase does not change the hydrodynamic volume of flax galactan (despite considerable cleavage of Gal moieties), suggesting a complex ¿secondary¿ structure of the polymer

Occurrence of cell-specific galactan is coinciding with bast fiber developmental transition in flax

Bast fiber peels of developing flax (Linum usitatissimum L.) stem contain tissue-specific soluble (1 --> 4)-beta-galactan. The occurrence and localization of this polymer have been investigated at various stages of bast fiber development. Tissue-specific galactan (molecular mass >2000 kDa) emerged right below the snap point-the manually identified spot on the stem, above which the fiber cells elongate, while below no more elongation occurs, but intensive secondary cell wall thickening takes place. In the course of plant development the amount of tissue-specific galactan gradually declined and in mature plants the polymer disappeared from the fraction, being either degraded or fixed within the cell wall. The immunolocalization of (1 --> 4)-beta-galactans with LM5 antibody revealed that in flax stem these polymers were present only in bast fiber cells. Two layers were well pronounced within the secondary cell wall, the density of gold particles in the inner layer was 5.2 +/- 1.5 times higher than in the outer layer. To distinguish soluble galactan from other (1 --> 4)-beta-galactans, the stem sections were treated with buffer, which elutes buffer-soluble galactan. The soluble high molecular mass (1 --> 4)-beta-galactan is a bast fiber cell-specific polymer, emerging at the transition from cell elongation to cell wall thickening. It is localized in the inner portion of the secondary cell wall and is modified or degraded in the course of further plant development. This polymer belongs to the rarely observed plant cell wall polysaccharides, which only occurs at one specific stage of cell development, suggesting that it could play a prominent role in cellulose deposition and secondary cell wall formation in flax fibers.. (C) 2003 Elsevier B.V. All rights reserved

Composition and distribution of cell wall phenolic compounds in flax (Linum usitatissimum L.) stem tissues

Cell wall phenolic compounds were analysed in xylem and bast fibre-rich peels of flax stems by biochemical, histochemical and ultrastructural approaches. Localization of cell wall phenolics by the enzyme-gold method using laccase revealed several gold particle distribution patterns. One of the major types (an even distribution of single gold particles) was present mainly in xylem, while the other (compact branched groups of ten–40 gold particles) was found both in xylem and fibre cells. The lignin content of the stem parts was estimated by the Klason procedure and by the thioglycolic acid assay, and the phenolic products recovered after alkaline cupric oxide oxidation of cell walls were analysed by GC. By combining chemical analysis data and the frequency of various gold particle types within the tissues, different patterns of gold particle distribution could be ascribed to certain cell wall phenolics; lignin was stained as evenly distributed single gold particles, while branched clusters represented hydroxycinnamic acids. The Klason procedure did not remove all the non-lignin components from flax fibres, known for their highly crystalline cellulose, and considerably overestimated the lignin content. The thioglycolic acid assay results were consistent with GC and microscopic observations