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6 recordsLinked to original sources
PubMed1979

Structural studies on the major component of Gladiolus style mucilage, an arabinogalactan-protein.

The major component of the Gladiolus style mucilage was shown to be an arabinogalactan-protein. The arabinogalactan-protein was isolated from the style extract by affinity chromatography with tridacnin (the galactose-binding lectin from the clam Tridacna maxima) coupled to Sepharose 4B. The isolated arabinogalactan-protein represents 40% of the soluble style extract; it contains 90% (w/w) carbohydrate and 3% protein. The major monosaccharides of the carbohydrate component are galactose and arabinose, in the proportions 6:1. A component with a similar composition was also isolated from the crude extract by precipitation with the beta-glucosyl artifical carbohydrate antigen. The protein moiety of the arabinogalactan-protein remained associated with the carbohydrate after chromatography in urea, and has high contents of serine, glutamic acid, aspartic acid, glycine and alanine. The arabinogalactan-protein is apparently chemically homogeneous; it eluted as a single symmetrical peak from Sepharose 4B, and three fractions collected across the peak were structurally similar. Ultracentrifugal studies showed it to be polydisperse in the mol.wt. range 150 000--400 000. The information obtained from methylation analyses, oxalic acid and enzymic hydrolyses is consistent with a model having a beta 1 leads to 3 galactan backbone, branched through C(O)6 to beta 1 leads to 6 galactan side chains. The arabinose is exclusively present as terminal alpha-L-arabinofuranosyl residues. Enzymic removal of the arabinose residues resulted in a marked decrease in solubility of the molecule. The localization of the arabinogalactan-protein in the mucilage of the style canal was demonstrated cytochemically. The possible roles of the arabinogalactan-protein in relation to recognition of compatible pollen and pollen-tube growth are discussed.

Amino Acids↗
PubMed2025

New insights into bryophyte arabinogalactan-proteins from a hornwort and a moss model organism.

Two bryophyte models, the hornwort Anthoceros agrestis (Anthoceros) and the moss Physcomitrium patens (Physcomitrium), were analyzed for the presence of arabinogalactan-proteins (AGPs), as the emergence of these signaling glycoproteins in evolution is still under debate. AGPs of both species had a galactan core structure similar to that of other bryophyte and fern AGPs, but different from angiosperm AGPs, as 1,6-linked pyranosidic galactose was almost absent. In the Physcomitrium AGP, furanosidic arabinose (Araf) linkages were mainly terminal (10%) or 5-linked (13%), while in Anthoceros, terminal Araf dominated (26%) and was accompanied by very low amounts of 1,3-Araf and pyranosidic terminal Ara. Unusual 3-O-methylated pyranosidic rhamnose, which has never been detected in cell walls of angiosperms, occurred in both bryophyte AGPs (5% in Anthoceros, 10% in Physcomitrium AGP). This was comparable to AGPs of other spore-producing land plants. A bioinformatic search in the genomes of 14 bryophyte species revealed that most hornworts lack sequences encoding GPI-anchored classical AGPs. Generally, hornworts contained fewer sequences for AGP protein backbones compared with the liverwort Marchantia polymorpha and the moss P. patens. All of them comprise sequences for chimeric AGPs, and among those, surprisingly xylogen-like AGPs. Homologous sequences encoding glycosyltransferases and other enzymes involved in the synthesis and decoration of the AGP galactan framework were present in all bryophyte genomes. Immunocytochemistry of Anthoceros tissue detected AGPs at the plasma membrane/cell wall interface but also at the tonoplast, suggesting new functions of AGPs in bryophytes.

Mucoproteins↗
PubMed2026

Trimming galactose side chains of arabinogalactan proteins alters pectin and hemicellulose deposition in secondary cell walls of Arabidopsis thaliana floral stem internodes.

Shaping the cell wall composition and structure to meet the requirements of different tissues and developmental stages relies on multiple actors, including arabinogalactan proteins (AGPs). Although the specific role of these proteins in cell wall dynamics is still under debate, especially in events involving significant remodeling of the cell wall, their carbohydrate motif, type II arabinogalactan (AGII), seems to be crucial for their function. This study aims to investigate the function of AGII, specifically the galactose residues of its side chains, in the structural organization of the cell wall during the cessation of elongation and the transition to secondary growth. To achieve this, we characterized floral stem internodes of Arabidopsis thaliana plants overproducing the chickpea βV-galactosidase protein (35S::βV-Gal plants), an enzyme that specifically hydrolyzes the β-(1,3)- and β-(1,6)-galactosyl residues of AGII. Changes induced in the cell wall by trimming galactose residues of AGII resulted in a noticeable increase in homogalacturonan methyl esterification. Additionally, these neutral galactose side chains may regulate hemicellulose-cellulose interactions and influence xylan distribution through the cellulose network, which in turn affects the deposition of lignin and determines its recalcitrance to enzymatic degradation.

Arabidopsis↗
PubMed2026

A maize GT14 family glycosyltransferase affects cell wall composition and carbohydrate export from source leaves.

Sucrose translocation from photosynthetic leaves to distant parts of a plant, such as seeds and roots, is a critical aspect of plant growth and development and a major determinant of crop yield. To identify genes contributing to this process in maize (Zea mays), we isolated four allelic mutants, carbohydrate partitioning defective7, 48, 49 (cpd7, cpd48, cpd49) and a UniformMu insertion (mu1049954), all of which exhibited reduced growth and fertility and hyperaccumulation of starch and soluble sugars in mature leaves. Consistent with carbohydrate accumulation, cpd7 mutants exhibited reduced sucrose export from mature leaves. Cpd7 encodes a Golgi-resident glucuronosyltransferase belonging to the Glycosyltransferase14 (GT14) family, which is involved in decoration of type II arabinogalactan proteins. No previously described GT14 mutants exhibit reduced sucrose transport or carbohydrate partitioning defects. Additionally, we show that mature leaves of cpd7 mutants have reduced cellulose content and an altered cell wall composition. Further, cpd7 mutants exhibit ectopic phloem lignification likely as a compensatory mechanism for reduced cell wall integrity. Collectively, our data suggest that Cpd7 functions to facilitate cell wall development in the phloem, which is required for efficient sucrose export from mature maize leaves.

Zea mays↗
PubMed1978

[Chemical structure of mycobacterial cell wall].

The immunostimulant properties of mycobacterial cell walls have led to a thorough study of their structure and to isolation of their components. The backbone of the mycobacterial cell wall is of a covalent structure ("covalent skeleton") made up of two polymers covalently linked by phosphodiester linkages: a arabinogalactan mycolate and a peptidoglycan. To this covalent structure are attached, in a rather ill defined manner, proteins or lipoproteins and, in pathogenic and most vaccinating strains, a partly amidated poly-alpha-L-glutamic acid. The mycobacterial cell wall also contains about 25% of free lipids, i.e. lipids which can be extracted by neutral solvents.

Amino Acids↗