▪ Abstract Rhamnogalacturonan II (RG-II) is a structurally complex pectic polysaccharide that was first identified in 1978 as a quantitatively minor component of suspension-cultured sycamore cell walls. Subsequent studies have shown that RG-II is present in the primary walls of angiosperms, gymnosperms, lycophytes, and pteridophytes and that its glycosyl sequence is conserved in all vascular plants examined to date. This is remarkable because RG-II is composed of at least 12 different glycosyl residues linked together by more than 20 different glycosidic linkages. However, only a few of the genes and proteins required for RG-II biosynthesis have been identified. The demonstration that RG-II exists in primary walls as a dimer that is covalently cross-linked by a borate diester was a major advance in our understanding of the structure and function of this pectic polysaccharide. Dimer formation results in the cross-linking of the two homogalacturonan chains upon which the RG-II molecules are constructed and ...

RHAMNOGALACTURONAN II: Structure and Function of a Borate Cross-Linked Cell Wall Pectic Polysaccharide

The catalytic subunit of cellulose synthase is shown to be associated with the putative cellulose-synthesizing complex (rosette terminal complex [TC]) in vascular plants. The catalytic subunit domain of cotton cellulose synthase was cloned using a primer based on a rice expressed sequence tag (D41261) from which a specific primer was constructed to run a polymerase chain reaction that used a cDNA library from 24 days postanthesis cotton fibers as a template. The catalytic region of cotton cellulose synthase was expressed in Escherichia coli, and polyclonal antisera were produced. Colloidal gold coupled to goat anti-rabbit secondary antibodies provided a tag for visualization of the catalytic region of cellulose synthase during transmission electron microscopy. With a freeze-fracture replica labeling technique, the antibodies specifically localized to rosette TCs in the plasma membrane on the P-fracture face. Antibodies did not specifically label any structures on the E-fracture face. Significantly, a greater number of immune probes labeled the rosette TCs (i.e., gold particles were 20 nm or closer to the edge of the rosette TC) than did preimmune probes. These experiments confirm the long-held hypothesis that cellulose synthase is a component of the rosette TC in vascular plants, proving that the enzyme complex resides within the structure first described by freeze fracture in 1980. In addition, this study provides independent proof that the CelA gene is in fact one of the genes for cellulose synthase in vascular plants.

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Immunogold Labeling of Rosette Terminal Cellulose-Synthesizing Complexes in the Vascular Plant Vigna angularis

Cellulose is one of the major commercial products of Sweden and constitutes the most abundant of the natural polymer systems. Thus, it is of interest to review the molecular design and architecture of cellulose with particular reference to the controls of its biosynthesis. The bioassembly process is highly ordered and structured, reflecting the intricate series of events which must occur to generate a thermodynamically metastable crystalline submicroscopic, ribbonlike structure. The plant cell wall is an extremely complex composite of many different polymers. Cellulose is the “reinforcing rod” component of the wall. True architectural design demands a polymer which can withstand great flexing and torsional strain. Using comparative Hydrophobic Cluster Analysis of a bacterial cellulose synthase and other glycosyl transferases, the multidomain architecture of glycosyl transferases has been analyzed. All polymerization reactions which are processive require at least three catalytic sites located on ...

The Biosynthesis of Cellulose

Myrmecochory, or seed dispersal by ants, is a dispersal syndrome found among several thousand plant species occupying different ecosystems and geographical regions. Typically, ants benefit from consuming a lipid-rich appendage on the seed and in return provide seed dispersal service to the plant. Several hypotheses have been proposed to explain the selective advantage for plants resulting from myrmecochory, including directed dispersal, dispersal for distance and escape from seed predators. I contrast the evidence available in the literature for these hypotheses and distinguish the studies on the basis of ecosystem and plant growth forms. The predator-avoidance and the distance dispersal hypotheses were supported in most studies that addressed them, and the directed dispersal hypothesis was supported in about half of the studies that tested it. Multiple hypotheses were supported in most studies that tested more than one hypothesis, suggesting that the various selective advantages conferred from myrmecochory are seldom exclusive. I also review evidence for the hypothesis that plants have evolved adaptations both for selecting seed dispersers and for manipulating the behavior of those dispersers. Based on this evidence, I argue that focusing future research on the evolution of partner choice by myrmecochores and its effects on the overall plant fitness will be more fruitful than putting an emphasis on classifying the selective advantage to plants into distinct categories and test for their existence separately.

Choosing benefits or partners: a review of the evidence for the evolution of myrmecochory

Numerous evolutionary innovations were required to enable freshwater green algae to colonize terrestrial habitats and thereby initiate the evolution of land plants (embryophytes). These adaptations probably included changes in cell-wall composition and architecture that were to become essential for embryophyte development and radiation. However, it is not known to what extent the polymers that are characteristic of embryophyte cell walls, including pectins, hemicelluloses, glycoproteins and lignin, evolved in response to the demands of the terrestrial environment or whether they pre-existed in their algal ancestors. Here we show that members of the advanced charophycean green algae (CGA), including the Charales, Coleochaetales and Zygnematales, but not basal CGA (Klebsormidiales and Chlorokybales), have cell walls that are comparable in several respects to the primary walls of embryophytes. Moreover, we provide both chemical and immunocytochemical evidence that selected Coleochaete species have cell walls that contain small amounts of lignin or lignin-like polymers derived from radical coupling of hydroxycinnamyl alcohols. Thus, the ability to synthesize many of the components that characterize extant embryophyte walls evolved during divergence within CGA. Our study provides new insight into the evolutionary window during which the structurally complex walls of embryophytes originated, and the significance of the advanced CGA during these events.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-313X.2011.04686.x

The charophycean green algae provide insights into the early origins of plant cell walls

Fatty acids and diacylglycerols from elaiosomes of some ant-dispersed seeds

The two-layered, fibrillar cell wall of Mougeotia C. Agardh sp. consisted of 63.6% non-cellulosic carbohydrates and 13.4% cellulose. The orientation of cellulose microfibrils in the native cell wall agrees with the multinet growth hypothesis, which has been employed to explain the shift in microfibril orientation from transverse (inner wall) toward axial (outer wall). Monosaccharide analysis of isolated cell walls revealed the presence of ten sugars with glucose, xylose and galactose most abundant. Methylation analysis of the acid-modified, 1 N NaOH insoluble residue fraction showed that it was composed almost exclusively of 4-linked glucose, confirming the presence of cellulose. The major hemicellulosic carbohydrate was semi-purified by DEAE Sephacel (Cl−) anion-exchange chromatography of the hot 1 N NaOH soluble fraction. This hemicellulose was a xylan consisting of a 4-xylosyl backbone and 2,4-xylosyl branch points. The major hot water soluble neutral polysaccharide was identified as a 3-linked galactan.

Mougeotia cell wall composition is similar to that of (Charophyceae) and has homologies with vascular plant cell walls. Our observations support transtructural evidence which suggests that members of the Charophyceae represent the phylogenetic line that gave rise to vascular plants. Therefore, the primary cell walls of vascular plants many have evolved directly from structures typical of the filamentous green algal cell walls found in the Charophyceae.

The composition and phylogenetic significance of the mougeotia (charophyceae) cell wall1

A method of producing cellulose of amorphous character by subjecting cellulose-producing organisms to a magnetic field substantially greater than 0.5 gauss and preferably at least about 500 gauss. The cellulose produced in the presence of a magnetic field is of an amorphous nature with increased water absorptivity and decreased crystallinity.

Magnetic alteration of cellulose during its biosynthesis

Cell walls of the generic phase of the freshwater red alga Lemanea annulata Kutz were mechanically isolated and chemically characterized. Walls consisted mainly of polysaccharide with lesser quantities of associated protein and lipid. The major wall component was alkali-soluble xylan, comprised mainly of 4-linked β-xylopyranosyl residues and small amounts of 3-O-substituted β-xylopyranosyl residues. Hot water extracts yielded non-sulfated polymers, with 3- or 3,4-linked β-galactosyl residues alternating with 4-linked α-glucuronosyl residues as the predominant structural features. This acid polysaccharide shares many characteristics of the mucilage previously described from the freshwater genus Batrachospermum. Isolated cell walls of L. annulata contained approximately 6% cellulose. Cellobiohydrolase/colloidal gold labelling of cell walls revealed β-4-glycan throughout the fibrillar portion of the wall. Wall protein consisted of at least 17 amino acids, of which threonine and alanine were the most abundant. Polysaccharides of the cell walls of L. annulata differ from those of marine red algae and are similar to those described for other Batrachospermales.

Michael R. Gretz

Papers

Fatty acids and diacylglycerols from elaiosomes of some ant-dispersed seeds

The composition and phylogenetic significance of the mougeotia (charophyceae) cell wall1

Magnetic alteration of cellulose during its biosynthesis

Chemical composition of the cell walls of the freshwater red alga lemanea annulata (batrachospermales)

Differentiation between glucose, mannose, allose and galactose in plant glycosides by high-performance liquid chromatographic analysis