Plant Science

Pectin is a complex polysaccharide present in the plant cell wall, whose composition is constantly remodelled to adapt to environmental or developmental changes. Mutants with altered pectin composition have been reported to exhibit altered stress or pathogen resistance. Understanding the link between mutant phenotypes and their pectin composition requires robust analytical methods to detect changes in the relative monosaccharide composition. Here, we describe a quick and efficient gas chromatography–mass spectrometry (GC–MS)-based method that allows the differential analysis of pectin monosaccharide composition in plants under different conditions or between mutant plants and their respective wild types. Pectin is extracted from seed mucilage or from the alcohol-insoluble residue prepared from leaves or other organs and is subsequently hydrolysed with trifluoracetic acid. The resulting acidic and neutral monosaccharides are then derivatised and measured simultaneously by GC–MS.

Key features

• Comparative analysis of monosaccharide content in Arabidopsis-derived pectin between different genotypes or different treatments.

• Procedures for two sources of pectin are shown: seed coat mucilage and alcohol-insoluble residue.

• Allows quick analyses of neutral and acidic monosaccharides simultaneously.

Graphical overview

Xyloglucan is one of the main components of the primary cell wall in most species of plants. This protocol describes a method to analyze the composition of the enzyme-accessible and enzyme-inaccessible fractions of xyloglucan in the model species Arabidopsis thaliana. It is based on digestion with an endoglucanase that attacks unsubstituted glucose residues in the backbone. The identities and relative amounts of released xyloglucan fragments are then determined using MALDI-TOF mass spectrometry.

In addition to synthesizing and secreting copious amounts of pectic polymers (Young et al., 2008), Arabidopsis thaliana seed coat epidermal cells produce small amounts of cellulose and hemicelluloses typical of secondary cell walls (Voiniciuc et al., 2015c). These components are intricately linked and are released as a large mucilage capsule upon hydration of mature seeds. Alterations in the structure of minor mucilage components can have dramatic effects on the architecture of this gelatinous cell wall. The immunolabeling protocol described here makes it possible to visualize the distribution of specific polysaccharides in the seed mucilage capsule.

The plant cell wall is primarily composed of the polysaccharides cellulose, hemicellulose and pectin. The structural and compositional complexity of these components are important for determining cell wall function during plant growth. Moreover, cell wall structure defines a number of functional properties of plant-derived biomass, such as rheological properties of foods and feedstock suitability for the production of cellulosic biofuels. A typical characterization of cell wall chemistry in the molecular biology lab consists of a mild acid hydrolysis for the quantification of hemicellulose and pectin-derived monomers and a separate analysis of cellulose by the Updegraff method. We have adopted a streamlined ‘one-step two-step’ hydrolysis protocol that allows for the simultaneous determination of cellulose content, neutral sugars, and uronic acids by high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) of paired samples. In our work, this protocol has largely replaced Updegraff cellulose quantification and hydrolysis with 2 M TFA for the determination of matrix polysaccharide composition at the micro scale.

The Arabidopsis thaliana seed coat epidermis produces copious amounts of mucilage polysaccharides (Haughn and Western, 2012). Characterization of mucilage mutants has identified novel genes required for cell wall biosynthesis and modification (North et al., 2014). The biochemical analysis of seed mucilage is essential to evaluate how different mutations affect cell wall structure (Voiniciuc et al., 2015c). Here we describe a robust method to screen the monosaccharide composition of Arabidopsis seed mucilage using ion chromatography (IC). Mucilage from up to 48 samples can be extracted and prepared for IC analysis within 24 h (only 4 h hands-on). Furthermore, this protocol enables fast separation (31 min per sample), automatic detection and quantification of both neutral and acidic sugars.

The Arabidopsis thaliana seed coat produces large amounts of cell wall polysaccharides, which swell out of the epidermal cells upon hydration of the mature dry seeds. While most mucilage polymers immediately diffuse in the surrounding solution, the remaining fraction tightly adheres to the seed, forming a dense gel-like capsule (Macquet et al., 2007). Recent evidence suggests that the adherence of mucilage is mediated by complex interactions between several cell wall components (Griffiths et al., 2014; Voiniciuc et al., 2015a). Therefore, it is important to evaluate how different cell wall mutants impact this mucilage property. This protocol facilitates the analysis of monosaccharides in sequentially extracted mucilage fractions, and quantifies the detachment of each component from seeds.

Root is a perfect model for studying the mechanisms of plant cell growth. Along the root length, several zones where cells are at different stages of development can be visualized (Figure 1). The dissection of the root on these zones allows the investigation of biochemical and genetic aspects of different growth steps. Maize primary root is much more massive than the root of other Monocots and thus more convenient for such type of research. Plant cell wall, mainly consisting of polysaccharides, plays an important role in plant life. Therefore, measurement of plant carbohydrate content and glycoside-modifying enzyme activity in plant cells has become an important aspect in plant physiology. One of the well-documented changes of hemicelluloses molecules during elongation growth of monocots cells is the decrease of arabinose substitution of glucuronoarabinoxylans. This might be caused by changes in synthesis of this polysaccharide or by the action of arabinofuranosidases. Here, we describe the protocol of spectrophotometric measuring of arabinofuranosidase activity in maize root by the rate of hydrolysis of chromogenic substrate (4-nitrophenyl α-L-arabinofuranoside).


Figure 1. Scheme of plant material collection for further arabinofuranosidase assay. Four-day-old dark-grown maize seedling (left panel). Different zones of primary maize root and corresponding stages of cell development, according to Kozlova et al. (2012) (right panel).

Various types of cell wall compositions have evolved to fulfill a wide range of biological roles during the diversification of land plants. (1;3,1;4)-β-D-glucan (MLG) is a defining feature of the cell walls in the order Poales (Yokoyama and Nishitani, 2004), which has multiple functions associated with metabolic, growth, and defense systems. MLG is also a characteristic component of the matrix polysaccharides that undergo turnover and metabolism, depending on the tissue and the stage of development (Kido et al., 2015). Determining the extracellular localization of MLG is essential for elucidating its functions. Electron microscopy immunogold labeling analysis is a useful technique, which provides an accurate representation of the extracellular distribution of MLG. This strategy is also applicable to various kinds of cell wall polysaccharides, which have key roles in regulating growth and differentiation in each plant species.

Hydroxyproline (Hyp) O-galactosylation is a plant-specific post-translational modification found in extracellular glycoproteins such as arabinogalactan proteins (AGPs). Hyp O-galactosylation is mediated by Hyp O-galactosyltransferase (HPGT) that catalyzes the transfer of a D-galactopyranosyl residue to the hydroxyl group of Hyp residues of peptides from the sugar donor UDP-α-D-Gal. Here we describe an LC/MS-based method for the detection of Hyp O-galactoside.

Starch synthases are one class of key enzymes involving in the synthesis of cereal starch, which transfer glucose from ADP-glucose to the non-reducing end of pre-existing α-(1-4)-liked glucosyl chains of amylopectin. This protocol is highly reproducible for assaying activities for starch synthase I and IIIa in wheat and barley endosperm at qualitative level and quantitative level. The protocol includes separating proteins isolated from developing endosperm with native-PAGE containing glycogen from oyster, incubating protein gels with ADP-glucose solution, and staining gels with iodine solution. The method allows researchers to compare the levels or changes of starch synthase activities.