β-1,3-Glucans in the cell walls of cotton fibres (Gossypium arboreum L.)

β-1,3-Glucan synthesis, novel supramolecular self-assembly, characterization and application

β-1,3-Glucans are ubiquitously observed in various biological systems with diverse physio-ecological functions, yet their underlying assembly mechanism and multiscale complexation in vitro remains poorly understood. Here, we provide for the first-time evidence of unidentified β-1,3-glucan supramolecular complexation into intricate hierarchical architectures over several length scales. We mediated these unique assemblies using a recombinantly produced β-1,3-glucan phosphorylase (Ta1,3BGP) by fine-tuning solution conditions during particle nucleation and growth. We report a synthesis of interconnected parallel hexagonal lamellae composed of 8 nm thick sheets of highly expanded paracrystals. The architecture consists of β-1,3-glucan triple-helices with considerable inter-intra hydrogen bonding within, as well as in between adjacent triple-helices. The results extend our understanding of β-1,3-glucan molecular organization and shed light on different aspects of the crystallization processes of biomolecules into structures unseen by nature. The presented versatile synthesis yields new materials for diverse medical and industrial applications.

Composition of the cell walls of Nicotiana alata Link et Otto pollen tubes

Cell walls isolated from pollen of Nicotiana alata germinated in vitro contain glucose and arabinose as the predominant monosaccharides. Methylation analysis and cytochemical studies are consistent with the major polysaccharides being a (1→3)-β-D-glucan (callose) and an arabinan together with small amounts of cellulose. The cell walls contain 2.8% uronic acids. Alcian blue stains the pollen-tube walls intensely at the tip, indicating that acidic polysaccharides are concentrated in the tip. Synthetic aniline-blue fluorochrome is specific primarily for (1→3)-β-D-glucans and stains the pollen-tube walls, except at the tip. Protein (1.5%), containing hydroxyproline (2.4%), is present in the cell wall.

Influence of external factors on callose and cellulose synthesis during incubation in vitro of intact cotton fibres with [(14)C]sucrose

Seed clusters, with adhering fibres, from individual locules of 36-d-old fruit capsules of Gossypium arboreum L. were fed with [(14)C]sucrose in vitro. The fibres synthesised, under standard conditions, (1→3)-β-D-glucan (callose) and (1→4)-β-D-glucan (cellulose) in the ratio of approx. 2:1. Under a great variety of different conditions this product ratio remained more or less constant, even when total glucan synthesis was strongly inhibited with 2,4-dinitrophenol or phloretin, or when stimulated with abscisic acid. In attempts to favour cellulose synthesis, no conditions were found where the ratio was substantially reduced. On the other hand, the ratio could be appreciably increased by inhibiting cellulose synthesis, e.g. with 2,6-dichlorobenzonitrile or coumarin, by anionic detergents such as sodium dodecyl sulphate, by low temperatures, or by increasing the osmotic strength of the incubation medium up to conditions causing plasmolysis. Specific degradation of callose, during incubation of the seed clusters, by exogenous exo-(1→3)-β-D-glucanase significantly diminished incorporation of radioactivity into cellulose.

Specific and direct measurement of theβ-1,3-glucan in developing cotton fiber

The reaction of N,N-diethylaziridinium chloride with raw cotton (Gossypium hirsutum L.) seed fibers to introduce N,N-diethylaminoethyl (DEAE) substituents at a low degree of substitution was used for demonstrating the presence of O(4)H, characteristic of a β-1,3-glucan. The derivatized 1,3-glucan/cellulose was hydrolyzed to DEAE-glucoses that were analyzed by gas-liquid chromatography. Capillary columns proved effective for measuring the small amounts of 4-O-DEAE-glucose in the presence of major amounts of 2-O- and 6-O-DEAE-glucoses. Analyses of raw cotton fibers were carried out through fiber development (20, 27, 34, 41 and 48 d post anthesis, DPA) and field exposure (62, 83 and 104 DPA) periods. The yields of 4-O- and other individual DEAE-glucoses and the yield of 4-O-DEAE-glucose in relation to 2-O-DEAE-glucose were particularly informative concenring the role of the β-1,3-glucan in cellulose. The results confirmed the early production and almost immediate decrease of the β-1,3-glucan and demonstrated continued production of accessible cellulose followed by a sharp decrease in accessibility after boll opening. The β-1,3-glucan content of the raw cotton fiber, estimated from the yield of 4-O-DEAE-glucose (representing 1,3-glucan) and the yield of 2-O-DEAE-glucose (approximating 1,3-glucan plus cellulose) was 10%, 4%, 1% and 0.6% at, in the order given, 20, 27, 48, and 104 DPA. These results are in general agreement with other conventional analyses.

Glucan synthesis by intact cotton fibres fed with different precursors at the stages of primary and secondary wall formation

Seed clusters of individual locules from fruit capsules of Gossypium arboreum L. with adhering intact fibres were fed with radioactive uridinediphosphoglucose (UDPG), guanosinediphosphoglucose (GDPG), glucose and sucrose. The incorporation into high molecular weight glucans of the fibres was studied. For primary wall fibres, UDPG at 1 mM was by far the best precursor, whereas sucrose was the best precursor for secondary wall fibres. No competition was observed between the incorporation of glucose from UDPG and from sucrose when the two were fed simultaneously to secondary wall fibres, indicating that their metabolic pathways are well separated when they are fed from the apoplast. Inhibitors of respiratory ATP-formation strongly inhibited incorporation of sucrose but not that of UDPG. Sucrose incorporation was studied at five different stages of development of the cotton fibres. At the stage of most intense secondary wall formation the incorporation rate was about 300 times that during primary wall formation (24 days post anthesis (DPA)). Incorporation from 1 mM UDPG or GDPG by secondary wall fibres (35 DPA) was less than twice that of primary wall fibres (22 DPA), indicating that the two sugar nucleotides are not readily used as precursors for secondary wall cellulose when they are fed to the exterior of intact cells. The high molecular weight non-cellulosic glucans formed from UDPG and sucrose at 5 and 1,000 μM were solubilized in strongly alkaline solutions or dimethyl-sulfoxide (DMSO) and were partially characterized by degradation with an exo-β-1,3-glucanase. After feeding for one hour, at most 1/3 of the radioactivity in high molecular weight material was found in cellulose and at least 2/3 in β-1,3-glucan. The proportions varied little for fibres in the age range of 30 to 48 DPA when sucrose was the precursor although the total incorporation varied by a factor of about four. The fact that at all stages of secondary wall formation β-1,3-glucan is synthesized at a very high rate, but that the total amount in the cell wall does not exceed 2% in the later stages of wall formation, can be interpreted in terms of a high turnover of this polysaccharide if it is assumed that wound effects are negligible in the system under study.

Changes in the composition of cotton fibre cell walls during development

Purified cell walls, prepared from cotton fibres (Gossypium arboreum L.) at different growth stages, were subjected to successive extractions to give pectic, hemicellulosic, and α-cellulosic fractions. The protein content and sugars obtained after hydrolysis of the total cell walls and of the various fractions were quantitatively estimated. The amount of protein in the fibre cell walls from one ovule reached a maximum value at the end of the elongation growth, decreased, and then reached a second maximum at the end of the secondary wall deposition. The absolute amounts of fucose, galactose, mannose, rhamnose, arabinose, uronic acid, and non-cellulosic glucose residues all reached a maximum at the end of the primary wall formation or at the beginning of the secondary wall formation. Only the absolute amounts of xylose and of the cellulosic glucose residues increased until the end of the fibre development. Most conspicuous was the decrease in the absolute amounts of non-cellulosic glucose and of arabinose residues during the secondary wall formation, possibly indicating a turnover of at least some of the hemicellulosic wall material.