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Charophyte green algae (CGA) are assigned to be the closest relatives of land plants and therefore enlighten processes in the colonization of terrestrial habitats. For the transition from water to land, plants needed significant physiological and structural changes, as well as with regard to cell wall composition. Sequential extraction of cell walls of Nitellopsis obtusa (Charophyceae) and Spirogyra pratensis (Zygnematophyceae) offered a comparative overview on cell wall composition of late branching CGA. Because arabinogalactan-proteins (AGPs) are considered common for all land plant cell walls, we were interested in whether these special glycoproteins are present in CGA. Therefore, we investigated both species with regard to characteristic features of AGPs. In the cell wall of Nitellopsis, no hydroxyproline was present and no AGP was precipitable with the β-glucosyl Yariv's reagent (βGlcY). By contrast, βGlcY precipitation of the water-soluble cell wall fraction of Spirogyra yielded a glycoprotein fraction rich in hydroxyproline, indicating the presence of AGPs. Putative AGPs in the cell walls of non-conjugating Spirogyra filaments, especially in the area of transverse walls, were detected by staining with βGlcY. Labelling increased strongly in generative growth stages, especially during zygospore development. Investigations of the fine structure of the glycan part of βGlcY-precipitated molecules revealed that the galactan backbone resembled that of AGPs with 1,3- 1,6- and 1,3,6-linked Galp moieties. Araf was present only in small amounts and the terminating sugars consisted predominantly of pyranosidic terminal and 1,3-linked rhamnose residues. We introduce the term 'rhamnogalactan-protein' for this special AGP-modification present in S. pratensis., (© 2021 The Authors. The Plant Journal published by Society for Experimental Biology and John Wiley & Sons Ltd.)

Seagrasses evolved from monocotyledonous land plants that returned to the marine habitat. This transition was accomplished by substantial changes in cell wall composition, revealing habitat-driven adaption to the new environment. Whether arabinogalactan-proteins (AGPs), important signalling molecules of land plants, are present in seagrass cell walls is of evolutionary and plant development interest. AGPs of Zostera marina L. were isolated and structurally characterised by analytical and bioinformatics methods as well as by ELISA with different anti-AGP antibodies. Calcium-binding capacity of AGPs was studied by isothermal titration calorimetry (ITC) and microscopy. Bioinformatic searches of the Z. marina proteome identified 9 classical AGPs and a large number of chimeric AGPs. The glycan structures exhibit unique features, including a high degree of branching and an unusually high content of terminating 4-O-methyl-glucuronic acid (4-OMe GlcA) residues. Although the common backbone structure of land plant AGPs is conserved in Z. marina, the terminating residues are distinct with high amounts of uronic acids. These differences likely result from the glycan-active enzymes (glycosyltransferases and methyltransferases) and are essential for calcium-binding properties. The role of this polyanionic surface is discussed with regard to adaption to the marine environment.

Today, understanding of cell wall evolution is incomplete due to limited knowledge of cell wall structure of non-flowering plants. Besides polysaccharides, proteoglycans like arabinogalactan-proteins are important constituents of the cell wall of most if not all seed plants. This article provides the first detailed characterization of AGPs from a lycophyte and different ferns, which are the closest living relatives to seed plants. The amount of protein in fern AGPs (6-12%) was in a range comparable to most seed plant AGPs. However, it was higher for Lycopodium AGP (17%). The carbohydrate moieties of investigated AGPs showed typical features known for type-II arabinogalactans from seed plants and showed cross-reaction with polyclonal antibodies raised against Echinacea AGP. On the other hand, unusual structural components like high quantities of pyranosidic arabinose residues for Lycopodium AGP and 3-O-methyl-rhamnose for fern AGPs have been detected., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Arabinogalactan-proteins (AGPs) are important proteoglycans of plant cell walls. They seem to be present in most, if not all seed plants, but their occurrence and structure in bryophytes is widely unknown and actually the focus of AGP research. With regard to evolution of plant cell wall, we isolated AGPs from the three mosses Sphagnum sp., Physcomitrella patens and Polytrichastrum formosum. The moss AGPs show structural characteristics common for AGPs of seed plants, but also unique features, especially 3-O-methyl-rhamnose (trivial name acofriose) as terminal monosaccharide not found in arabinogalactan-proteins of angiosperms and 1,2,3-linked galactose as branching point never found in arabinogalactan-proteins before., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Root extracts of the medicinal plant Pelargonium sidoides, native to South Africa, are used globally for the treatment of common cold and cough. Due to an increasing economic commercialization of P. sidoides remedies, wild collections of root material should be accompanied by effective methods for plant propagation like somatic embryogenesis. Based on this, the influence of arabinogalactan-proteins (AGPs) on somatic embryogenesis and plant propagation of P. sidoides has been investigated. High-molecular weight AGPs have been isolated from dried roots as well as from cell cultures of P. sidoides with yields between 0.1% and 0.9%, respectively. AGPs are characterized by a 1,3-linked Galp backbone, branched at C6 to 1,6-linked Galp side chains terminated by Araf and to a minor extent by GlcpA, Galp or Rhap. Treatment of explants of P. sidoides with AGPs from roots or suspension culture over 5.5 weeks resulted in effective stimulation of somatic embryo development and plant regeneration., (Copyright © 2016. Published by Elsevier Ltd.)

Flow cytometric investigations show binding of an isolated arabinogalactan-protein (AGP) from pressed juice of the aerial parts of Echinacea purpurea to the cell surface of human leucocytes. AGP demonstrates binding to lymphocytes, monocytes and granulocytes of different donors (n=8). Competition assays with two antibodies, directed against CD4 and CD8, revealed no interaction of AGP with these receptors, leading to the conclusion that binding of AGP to leucocytes is mediated via other structures.

Pressed juices from Echinacea purpurea are used as non-specific immunostimulants, and arabinogalactan-proteins (AGPs) are part of the active principle. An AGP fraction was isolated from pressed juice of E. purpurea by precipitation with ss-glucosyl Yariv reagent, followed by gel-permeation chromatography. Polyclonal antibodies directed against the carbohydrate moiety of this AGP fraction showed a preferential specificity for E. purpurea AGPs from pressed juice over those extracted from E. purpurea suspension culture and other plant species. Native AGPs purified from this AGP fraction by RP-HPLC were then deglycosylated for N-terminal protein sequencing resulting in the identification of three major polypeptides. They show characteristic motifs of classical AGPs but also some features of extensins, suggesting these may be "hybrid" hydroxyproline-rich glycoproteins (HRGPs).

Pressed juices of the aerial parts of Echinacea purpurea are used as non-specific immunostimulants, and arabinogalactan-proteins (AGPs) have been shown to be part of the active principle. Monoclonal antibodies against an AGP from pressed juice of Echinacea purpurea with complement-stimulating activity have been established by means of hybridoma techniques. To test the specificity of the antibodies, several other arabinogalactan-proteins from suspension cultures of Echinacea purpurea, the roots of Echinacea pallida, the aerial parts of Rudbeckia hirta, the roots of Baptisia tinctoria and gum arabic as well as an arabinogalactan from larch wood were tested in a competitive ELISA for cross reactivities. Chemical modifications at the periphery of the AGP molecules either by reduction of uronic acids or by dearabinosylation had no influence on the reactivity of the molecules towards the antibodies. For further characterization of the epitope, different Ara-Gal-oligosaccharides were used as antigens. A hexasaccharide consisting of a backbone of four molecules of 6-linked beta- D-Gal p, the second and the fourth of them branched at O-2 to an alpha- L-Ara f residue showed weak but reproducible cross reactivity, indicating that the antibodies may be at least in part directed to the carbohydrate moiety of the AGP. Testing of anti-AGP antibodies JIM 8 and LM 2 revealed good reactivity of LM 2 with the Echinacea AGP, whereas Jim 8 showed only very weak interaction.

An arabinogalactan-protein (AGP) from suspension culture medium of Malva sylvestris was isolated by precipitation with beta-glucosyl Yariv reagent, followed by gel-permeation chromatography. It revealed characteristic features of AGPs: a high amount of polysaccharide with a ratio of galactose to arabinose of 1.9 : 1, some uronic acids, and a small protein moiety with the main amino acids serine, alanine and hydroxyproline. The molecular weight was estimated to be 1.3 x 10(6) Da. Linkage analyses showed that the AGP is composed of a highly branched core polysaccharide of 3-, 6-, and 3,6-linked Galp residues with terminal Araf, GlcAp and Galp. Partial acid hydrolysis resulted in loss of Araf residues at the periphery of the molecule and heavily reduced its reactivity with beta-glucosyl Yariv antigen.