Non-cellulosic Polysaccharides Research Articles

GDP‐d‐mannose 3,5‐epimerase (GME) plays a key role at the intersection of ascorbate and non‐cellulosic cell‐wall biosynthesis in tomato

The GDP-D-mannose 3,5-epimerase (GME, EC 5.1.3.18), which converts GDP-d-mannose to GDP-l-galactose, is generally considered to be a central enzyme of the major ascorbate biosynthesis pathway in higher plants, but experimental evidence for its role in planta is lacking. Using transgenic tomato lines that were RNAi-silenced for GME, we confirmed that GME does indeed play a key role in the regulation of ascorbate biosynthesis in plants. In addition, the transgenic tomato lines exhibited growth defects affecting both cell division and cell expansion. A further remarkable feature of the transgenic plants was their fragility and loss of fruit firmness. Analysis of the cell-wall composition of leaves and developing fruit revealed that the cell-wall monosaccharide content was altered in the transgenic lines, especially those directly linked to GME activity, such as mannose and galactose. In agreement with this, immunocytochemical analyses showed an increase of mannan labelling in stem and fruit walls and of rhamnogalacturonan labelling in the stem alone. The results of MALDI-TOF fingerprinting of mannanase cleavage products of the cell wall suggested synthesis of specific mannan structures with modified degrees of substitution by acetate in the transgenic lines. When considered together, these findings indicate an intimate linkage between ascorbate and non-cellulosic cell-wall polysaccharide biosynthesis in plants, a fact that helps to explain the common factors in seemingly unrelated traits such as fruit firmness and ascorbate content.

The distribution of ester-linked ferulic acid in the cell walls of angiosperms

Ester-linked ferulic acid occurs in the cell walls of two major groups of angiosperms, the commelinid monocotyledons and the ‘core’ Caryophyllales, at concentrations >3.5 mg g−1 cell walls, and has been detected in primary cell walls by its autofluorescence using ultraviolet fluorescence microscopy. Both of these groups are resolved as monophyletic clades in phylogenetic trees constructed using gene sequences. In the primary cell walls of the commelinid monocotyledons, including the grasses (family Poaceae), the ferulic acid is ester-linked to the non-cellulosic polysaccharide glucuronoarabinoxylan. In contrast, in the ‘core’ Caryophyllales, the ferulic acid is ester-linked to the side chain arabinans and galactans of the pectic polysaccharide rhamnogalacturonan-1, at least in the family Amaranthaceae. In the walls of both angiosperm groups, a range of dehydrodiferulates have also been found. These are formed oxidatively via radical coupling and result in the cross linking of the polysaccharides to which they are attached. Much lower concentrations of ester-linked ferulic acid have been found in cell walls isolated from other angiosperms, although physiological stress conditions may cause increases in these concentrations. The polysaccharides to which the ferulic acid is attached to in the cell walls of these other angiosperms is unknown.

(1,3;1,4)-β-D-Glucans in Cell Walls of the Poaceae, Lower Plants, and Fungi: A Tale of Two Linkages

(1,3;1,4)-beta-D-glucans consist of unbranched and unsubstituted chains of (1,3)- and (1,4)-beta-glucosyl residues, in which the ratio of (1,4)-beta-D-glucosyl residues to (1,3)-beta-D-glucosyl residues appears to influence not only the physicochemical properties of the polysaccharide and therefore its functional properties in cell walls, but also its adoption by different plant species during evolution. The (1,3;1,4)-beta-D-glucans are widely distributed as non-cellulosic matrix phase polysaccharides in cell walls of the Poaceae, which evolved relatively recently and consist of the grasses and commercially important cereal species, but they are less commonly found in lower vascular plants, such as the horsetails, in algae and in fungi. The (1,3;1,4)-beta-D-glucans have often been considered to be components mainly of primary cell walls, but recent observations indicate that they can also be located in secondary walls of certain tissues. Enzymes involved in the depolymerisation of (1,3;1,4)-beta-D-glucans have been well characterized. In contrast, initial difficulties in purifying the enzymes responsible for (1,3;1,4)-beta-D-glucan biosynthesis slowed progress in the identification of the genes that encode (1,3;1,4)-beta-D-glucan synthases, but emerging comparative genomics and associated techniques have allowed at least some of the genes that contribute to (1,3;1,4)-beta-D-glucan synthesis in the Poaceae to be identified. Whether similar genes and enzymes also mediate (1,3;1,4)-beta-D-glucan biosynthesis in lower plants and fungi is not yet known. Here, we compare the different fine structures of (1,3;1,4)-beta-D-glucans across the plant kingdom, present current information on the genes that have been implicated recently in their biosynthesis, and consider aspects of the cell biology of (1,3;1,4)-beta-D-glucan biosynthesis in the Poaceae.

Arabinan Metabolism during Seed Development and Germination in Arabidopsis

Arabinans are found in the pectic network of many cell walls, where, along with galactan, they are present as side chains of Rhamnogalacturonan l. Whilst arabinans have been reported to be abundant polymers in the cell walls of seeds from a range of plant species, their proposed role as a storage reserve has not been thoroughly investigated. In the cell walls of Arabidopsis seeds, arabinose accounts for approximately 40% of the monosaccharide composition of non-cellulosic polysaccharides of embryos. Arabinose levels decline to approximately 15% during seedling establishment, indicating that cell wall arabinans may be mobilized during germination. Immunolocalization of arabinan in embryos, seeds, and seedlings reveals that arabinans accumulate in developing and mature embryos, but disappear during germination and seedling establishment. Experiments using 14C-arabinose show that it is readily incorporated and metabolized in growing seedlings, indicating an active catabolic pathway for this sugar. We found that depleting arabinans in seeds using a fungal arabinanase causes delayed seedling growth, lending support to the hypothesis that these polymers may help fuel early seedling growth.

Concomitant Changes in Viscoelastic Properties and Amorphous Polymers during the Hydrothermal Treatment of Hardwood and Softwood

The aim of this study was to understand how the molecular structures of amorphous polymers influence wood viscoelastic properties. Wood from oak and spruce was subjected to hydrothermal treatments at 110 or 135 degrees C. Wood rigidity, reflected by the wood storage modulus, showed different modification patterns according to the wood species or the temperature level. Because viscoelasticity is dependent on wood amorphous polymers, modifications of lignins and noncellulosic polysaccharides were examined. Hemicellulose degradation occurred only at 135 degrees C. In contrast, lignins displayed major structural alterations even at 110 degrees C. In oak lignins, the beta-O-4 bonds were extensively degraded and wood rigidity decreased dramatically during the first hours of treatment. Spruce lignins have a lower beta-O-4 content and, relative to oak, the wood rigidity decrease due to treatment was less pronounced. Wood rigidity was restored to its initial value by prolonged treatment, probably due to the formation of condensed bonds in cell wall polymers.

VTC4 Is a Bifunctional Enzyme That Affects Myoinositol and Ascorbate Biosynthesis in Plants

Myoinositol synthesis and catabolism are crucial in many multiceullar eukaryotes for the production of phosphatidylinositol signaling molecules, glycerophosphoinositide membrane anchors, cell wall pectic noncellulosic polysaccharides, and several other molecules including ascorbate. Myoinositol monophosphatase (IMP) is a major enzyme required for the synthesis of myoinositol and the breakdown of myoinositol (1,4,5)trisphosphate, a potent second messenger involved in many biological activities. It has been shown that the VTC4 enzyme from kiwifruit (Actinidia deliciosa) has similarity to IMP and can hydrolyze l-galactose 1-phosphate (l-Gal 1-P), suggesting that this enzyme may be bifunctional and linked with two potential pathways of plant ascorbate synthesis. We describe here the kinetic comparison of the Arabidopsis (Arabidopsis thaliana) recombinant VTC4 with d-myoinositol 3-phosphate (d-Ins 3-P) and l-Gal 1-P. Purified VTC4 has only a small difference in the V(max)/K(m) for l-Gal 1-P as compared with d-Ins 3-P and can utilize other related substrates. Inhibition by either Ca(2+) or Li(+), known to disrupt cell signaling, was the same with both l-Gal 1-P and d-Ins 3-P. To determine whether the VTC4 gene impacts myoinositol synthesis in Arabidopsis, we isolated T-DNA knockout lines of VTC4 that exhibit small perturbations in abscisic acid, salt, and cold responses. Analysis of metabolite levels in vtc4 mutants showed that less myoinositol and ascorbate accumulate in these mutants. Therefore, VTC4 is a bifunctional enzyme that impacts both myoinositol and ascorbate synthesis pathways.

Purification and Molecular Cloning of Xylanases from the Wood-Feeding Termite,Coptotermes formosanusShiraki

Coptotermes formosanus is one of the most destructive termites in the southern part of Japan as well as in the United States. Hemicellulose is a noncellulosic polysaccharide found in plant cell walls, and xylan is the major constituent of hemicellulose. Since hemicellulose prevents access of cellulolytic enzymes to cellulose, enzymatic hydrolysis of hemicellulose is beneficial for cellulose digestion. We purified three functional xylanases to homogeneity from C. formosanus for the first time. Elution profiles from the whole termite extract suggest that these three xylanases play major roles in xylan digestion in the gut of the termites. The corresponding cDNAs were successfully cloned based on the N-terminal amino acid sequences, encoding GHF11 xylanases. Reverse transcription-PCR using manipulated protozoan cells in the hindgut revealed that the corresponding genes were expressed in the symbiotic flagellate Holomastigotoides mirabile. These results suggest that the GHF11 xylanases that are produced by the symbiotic flagellates play a primary role in xylan degradation in C. formosanus.

Detailed mass balances of the autohydrolysis of Eucalyptus globulus at 170 oC

Autohydrolysis of Eucalyptus globulus was conducted at three different intensity levels typical for prehydrolysis kraft pulping as utilized for manufacturing dissolving pulp grades. The objective was to establish for the autohydrolysis process a detailed mass balance comprising the chemical composition of all three phases: the autohydrolysate, the released gas, and the solid residue. Carbohydrate determination involved both acid methanolysis combined with gas chromatography (GC) and sulfuric acid total hydrolysis with high performance anion exchange chromatography (HPAEC) coupled with pulsed amperometric detection (PAD); this allowed reliable quantification of neutral as well as acidic sugar units in cellulosic and non-cellulosic polysaccharides. Uronic acids present in the Eucalyptus globulus wood were progressively degraded through decarboxylation, leading to substantial carbon dioxide formation. The degree of acetylation of xylan remaining in the wood residue was clearly reduced, while the amount of bound acetyl groups in dissolved xylo-oligosaccharides (XOS) stayed relatively constant as a function of autohydrolysis intensity. The bulk of the lignin that was dissolved during autohydrolysis could be attributed to the acid-soluble lignin content of the wood. Only small amounts of Klason lignin were dissolved.

The Active Site of a Carbohydrate Esterase Displays Divergent Catalytic and Noncatalytic Binding Functions

Multifunctional proteins, which play a critical role in many biological processes, have typically evolved through the recruitment of different domains that have the required functional diversity. Thus the different activities displayed by these proteins are mediated by spatially distinct domains, consistent with the specific chemical requirements of each activity. Indeed, current evolutionary theory argues that the colocalization of diverse activities within an enzyme is likely to be a rare event, because it would compromise the existing activity of the protein. In contrast to this view, a potential example of multifunctional recruitment into a single protein domain is provided by CtCel5C-CE2, which contains an N-terminal module that displays cellulase activity and a C-terminal module, CtCE2, which exhibits a noncatalytic cellulose-binding function but also shares sequence identity with the CE2 family of esterases. Here we show that, unlike other CE2 members, the CtCE2 domain displays divergent catalytic esterase and noncatalytic carbohydrate binding functions. Intriguingly, these diverse activities are housed within the same site on the protein. Thus, a critical component of the active site of CtCE2, the catalytic Ser-His dyad, in harness with inserted aromatic residues, confers noncatalytic binding to cellulose whilst the active site of the domain retains its esterase activity. CtCE2 catalyses deacetylation of noncellulosic plant structural polysaccharides to deprotect these substrates for attack by other enzymes. Yet it also acts as a cellulose-binding domain, which promotes the activity of the appended cellulase on recalcitrant substrates. The CE2 family encapsulates the requirement for multiple activities by biocatalysts that attack challenging macromolecular substrates, including the grafting of a second, powerful and discrete noncatalytic binding functionality into the active site of an enzyme. This article provides a rare example of “gene sharing,” where the introduction of a second functionality into the active site of an enzyme does not compromise the original activity of the biocatalyst.

Dietary fiber and stomach cancer risk: a case–control study from Italy

Fiber intake has been inversely related to stomach cancer risk, although this issue is still controversial. A case-control study was conducted in Italy between 1997 and 2007, including 230 cases with incident, histologically confirmed stomach cancer, and 547 controls with acute, non-neoplastic diseases. Dietary habits were investigated through a validated food frequency questionnaire. Compared with the lowest quintile of intake, the multivariate odds ratios (ORs, including terms for major recognised confounding factors and total energy intake) for the highest quintile were 0.47 (95% confidence interval (CI): 0.28-0.79) for total fiber, 0.50 (95% CI: 0.30-0.85) for soluble non-cellulose polysaccharides (NCP), 0.39 (95% CI: 0.23-0.66) for total insoluble fiber, 0.54 (95% CI: 0.32-0.91) for insoluble NCP, 0.37 (95% CI: 0.22-0.64) for cellulose, and 0.59 (95% CI: 0.36-0.98) for lignin. With reference to the sources of fiber, an inverse association was found for fiber from vegetable (OR = 0.42, 95% CI: 0.24-0.72), and to a lesser extent from fruit (OR = 0.65, 95% CI: 0.38-1.10), but not for fiber from grain (OR = 1.25, 95% CI: 0.77-2.03). This study found an inverse relationship between stomach cancer risk and various types of fiber, derived, in particular, from vegetables and fruit.

Evolution of composition and content of soil carbohydrates following forest wildfires

The time evolution of the content and composition of carbohydrates was studied in the surface layer of forest soils non-affected and affected by wildfires. The low- and high-severity fires caused an immediate reduction of the C present as carbohydrates of 34% and 47–55%, respectively, which was due to the decrease of both hexoses and pentoses in two hydrolysis fractions (hydrolysate-A, non-cellulosic polysaccharides; hydrolysate-B, cellulosic polysaccharides). Carbohydrates tended to recover with time; however, values had still not reached the amounts found in the corresponding unburnt samples after 12–15 months. No difference between the unburnt and burnt samples was observed in the distribution of the neutral sugars in the hydrolysates over time. On a percentage basis, 72–92% of the total neutral sugars was extracted in hydrolysate-A (59 ± 7% hexoses; 24 ± 7% pentoses) and the rest, 8–28%, in hydrolysate-B (15 ± 5% hexoses; 2 ± 1% pentoses). The contribution of hexoses and pentoses to the neutral sugar pool was different between the two hydrolysis fractions being the hexoses/pentoses ratio higher for hydrolysate-B than for hydrolysate-A. The results also showed that the proportion of soil C present as carbohydrates-C rather than the total carbohydrates content should be used for monitoring short- and medium-term changes induced by fire in soil organic matter quality.

OCCURRENCE AND CHARACTERIZATION OF ARABINOGALACTAN-LIKE PROTEINS AND HEMICELLULOSES IN MICRASTERIAS (STREPTOPHYTA)(1).

The cell wall of the green alga Micrasterias denticulata Bréb. ex Ralfs (Desmidiaceae, Zygnematophyceae, Streptophyta) was investigated to obtain information on the composition of component polysaccharides and proteoglycans to allow comparison with higher plants and to understand cell wall functions during development. Various epitopes currently assigned to arabinogalactan-proteins (AGPs) of higher plants could be detected in Micrasterias by immuno TEM and immunofluorescence methods, but the walls did not bind the β-d-glycosyl-Yariv (β-GlcY) reagent. Secretory vesicles and the primary wall were labeled by antibodies against AGPs (JIM8, JIM13, JIM14). Dot and Western blot experiments indicated a proteoglycan nature of the epitopes recognized, which consisted of galactose and xylose as major sugars by high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). Epitopes of alkali-soluble polysaccharides assigned to noncellulosic polysaccharides in higher plants could be detected and located in the wall during its formation. The polyclonal anti-xyloglucan (anti-XG) antibody labeled primary and secondary wall of Micrasterias, whereas the monoclonal antibody CCRC-M1, directed against the fucose/galactose side chain of xyloglucan (XyG), did not recognize any structures. Labeling by anti-XG antibody at the trans-sites of the dictyosomes and at wall material containing vesicles indicated that secretion of the epitopes occurred similar to higher plants. The presence of (1→3, 1→4)-β-glucan (mixed linked glucan) in the secondary cell wall but not in the primary cell wall of Micrasterias could be demonstrated by an antibody recognizing this glucan type, whereas (1→3)-β-glucan (callose) could not be detected. The analytical results revealed that alkali-soluble polysaccharides in the secondary wall of Micrasterias consist mostly of (1→3, 1→4)-β-d-glucan.

Compositional characterization and imaging of “wall-bound” acylesters of Populus trichocarpa reveal differential accumulation of acyl molecules in normal and reactive woods

Acylesterification is one of the common modifications of cell wall non-cellulosic polysaccharides and/or lignin primarily in monocot plants. We analyzed the cell-wall acylesters of black cottonwood (Populus trichocarpa Torr. & Gray) with liquid chromatography-mass spectrometry (LC-MS), Fourier transform-infrared (FT-IR) microspectroscopy, and synchrotron infrared (IR) imaging facility. The results revealed that the cell wall of dicotyledonous poplar, as the walls of many monocot grasses, contains a considerable amount of acylesters, primarily acetyl and p-hydroxycinnamoyl molecules. The "wall-bound" acetate and phenolics display a distinct tissue specific-, bending stress responsible- and developmental-accumulation pattern. The "wall-bound" p-coumarate predominantly accumulated in young leaves and decreased in mature leaves, whereas acetate and ferulate mostly amassed in the cell wall of stems. Along the development of stem, the level of the "wall-bound" ferulate gradually increased, while the basal level of p-coumarate further decreased. Induction of tension wood decreased the accumulation of the "wall-bound" phenolics while the level of acetate remained constant. Synchrotron IR-mediated chemical compositional imaging revealed a close spatial distribution of acylesters with cell wall polysaccharides in poplar stem. These results indicate that different "wall-bound" acylesters play distinct roles in poplar cell wall structural construction and/or metabolism of cell wall matrix components.

Changes in expansin activity and cell wall susceptibility to expansin action during cessation of internodal elongation in floating rice

We investigated the involvement of expansin action in determining the growth rate of internodes of floating rice (Oryza sativa L.). Floating rice stem segments in which rapid internodal elongation had been induced by submergence for 2 days were exposed to air or kept in submergence for 2 more days. Both treatments reduced the elongation rate of the internodes, and the degree of reduction was much greater in air-exposed stem segments than in continually submerged segments. These rates of internodal elongation were correlated with acid-induced cell wall extensibility and cell wall susceptibility to expansins in the cell elongation zone of the internodes, but not with extractable expansin activity. These results suggest that the reduced growth rate of internodes must be due, at least in part, to the decrease in acid-induced cell wall extensibility, which can be modulated through changes in the cell wall susceptibility to expansins rather than through expansin activity. Analysis of the cell wall composition of the internodes showed that the cellulosic and noncellulosic polysaccharide contents increased in response to exposure to air, but they remained almost constant under continued submergence although the cell wall susceptibility to expansins gradually declined even under continued submergence. The content of xylose in noncellulosic neutral sugars in the cell walls of internodes was closely and negatively correlated with changes in the susceptibility of the walls to expansins. These results suggest that the deposition of xylose-rich polysaccharides into the cell walls may be related to a decrease in acid-induced cell wall extensibility in floating rice internodes through the modulation of cell wall susceptibility to expansins.

Absorption of carbohydrate-derived nutrients in sows as influenced by types and contents of dietary fiber1

The current investigation was undertaken to study the absorption and plasma concentration of carbohydrate-derived nutrients [glucose, short-chain fatty acids (SCFA), and lactate] and the apparent insulin production in sows fed diets containing contrasting types and contents of dietary fiber. Six sows were fed 3 experimental diets, low fiber (LF; 177 g of dietary fiber and 44 g of soluble fiber/kg of DM), high soluble fiber (HF-S; 429 g of dietary fiber and 111 g of soluble fiber/kg of DM), and high insoluble fiber (HF-I; 455 g of dietary fiber and 74 g of soluble fiber/kg of DM), in a repeated crossover design. Variations in dietary concentration and solubility of dietary fiber were obtained by substituting starch-rich wheat and barley in the LF diet with dietary fiber-rich co-products (sugar beet pulp, potato pulp, pectin residue, brewers spent grain, pea hulls, and seed residue, which have distinct physicochemical properties). The main carbohydrate component of the LF diet was starch and nonstarch polysaccharides (cellulose and noncellulosic polysaccharides) for the 2 high dietary fiber diets. Consumption of the LF diet resulted in increased and rapid glucose absorption at 0 to 4 h postfeeding. With the HF-I diet, the glucose absorption pattern was similar but at a decreased rate, whereas it was decreased and delayed with the HF-S diet (diet, P < 0.001; time, P < 0.001). These differences were also reflected in the insulin response. The quantitative absorption of SCFA at 0 to 10 h postfeeding was greater when feeding the HF-S diet compared with the LF diet (P < 0.001) and intermediate when feeding the HF-I diet (P < 0.001). The study showed that feeding the high dietary fiber diets resulted in a increased and more uniform uptake of SCFA than when feeding the LF control. Moreover, the HF-S diet reduced diurnal variation in glucose and insulin concentrations.

Glucuronoarabinoxylan structure in the walls of Aechmea leaf chlorenchyma cells is related to wall strength

In CAM-plants rising levels of malic acid in the early morning cause elevated turgor pressures in leaf chlorenchyma cells. Under specific conditions this process is lethal for sensitive plants resulting in chlorenchyma cell burst while other species can cope with these high pressures and do not show cell burst under comparable conditions. The non-cellulosic polysaccharide composition of chlorenchyma cell walls was investigated and compared in three cultivars of Aechmea with high sensitivity for chlorenchyma cell burst and three cultivars with low sensitivity. Chlorenchyma layers were cut from the leaf and the non-cellulosic carbohydrate fraction of the cell wall fraction was analyzed by gas–liquid chromatography. Glucuronoarabinoxylans (GAXs) were the major non-cellulosic polysaccharides in Aechmea. The fine structure of these GAXs was strongly related to chlorenchyma wall strength. Chlorenchyma cell walls from cultivars with low sensitivity to cell burst were characterized by an A/X ratio of ca. 0.13 while those from cultivars with high sensitivity showed an A/X ratio of ca. 0.23. Xylose chains from cultivars with high cell burst sensitivity were ca. 40% more substituted with arabinose compared to cultivars with low sensitivity for cell burst. The results indicate a relationship in vivo between glucuronoarabinoxylan fine structure and chlorenchyma cell wall strength in Aechmea. The evidence obtained supports the hypothesis that GAXs with low degrees of substitution cross-link cellulose microfibrils, while GAXs with high degrees of substitution do not. A lower degree of arabinose substitution on the xylose backbone implies stronger cell walls and the possibility of withstanding higher internal turgor pressures without cell bursting.

Golgi transporters: opening the gate to cell wall polysaccharide biosynthesis

The synthesis of non-cellulosic polysaccharides occurs in the Golgi apparatus and requires a great number of metabolites (substrates and ions). Many enzymes use these substrates to add sugar residues to nascent polysaccharides chains or to introduce methyl and acetyl groups onto these polymers. Most of these metabolites are in the cytosol and their transport to the Golgi lumen is essential for proper polysaccharide biosynthesis. Different transporters activities have been described in Golgi membranes, but many more are thought to be present to provide all the substrates required for polysaccharide biosynthesis and to pump the ions for maintaining ionic homeostasis. Their functional analysis will help us to understand the role these transporters play in cell wall biosynthesis.

Competitive binding of pectin and xyloglucan with primary cell wall cellulose

Assemblies of pectin, xyloglucan and cellulose were studied in vitro using two ternary systems. In the first one, xyloglucan concentration varied, while pectin amount was kept constant. In the second one, pectin concentration varied, whereas xyloglucan amount was fixed. The use of ternary systems allowed to put forward the hypothesis that pectin/cellulose and xyloglucan/cellulose associations may exist together or separately, depending on the proportion of non-cellulosic polysaccharides in cell walls. It can be hypothesized that pectin plays a double role within primary cell walls: (i) pectin loosely bound to cellulose, in xyloglucan-rich cell walls, (ii) pectin associated with cellulose, in xyloglucan-poor cell walls.

Arabidopsis dynamin-like protein DRP1A: a null mutant with widespread defects in endocytosis, cellulose synthesis, cytokinesis, and cell expansion

Dynamin-related proteins are large GTPases that deform and cause fission of membranes. The DRP1 family of Arabidopsis thaliana has five members of which DRP1A, DRP1C, and DRP1E are widely expressed. Likely functions of DRP1A were identified by studying rsw9, a null mutant of the Columbia ecotype that grows continuously but with altered morphology. Mutant roots and hypocotyls are short and swollen, features plausibly originating in their cellulose-deficient walls. The reduction in cellulose is specific since non-cellulosic polysaccharides in rsw9 have more arabinose, xylose, and galactose than those in wild type. Cell plates in rsw9 roots lack DRP1A but still retain DRP1E. Abnormally placed and often incomplete cell walls are preceded by abnormally curved cell plates. Notwithstanding these division abnormalities, roots and stems add new cells at wild-type rates and organ elongation slows because rsw9 cells do not grow as long as wild-type cells. Absence of DRP1A reduces endocytotic uptake of FM4-64 into the cytoplasm of root cells and the hypersensitivity of elongation and radial swelling in rsw9 to the trafficking inhibitor monensin suggests that impaired endocytosis may contribute to the development of shorter fatter roots, probably by reducing cellulose synthesis.

Chemical valorization of agricultural by-products: Isolation and characterization of xylan-based antioxidants from almond shell biomass

The isolation of non-cellulosic polysaccharides from almond shells (AS) and their solid residue (ASR) after autohydrolysis was investigated using a two-step alkaline extraction without and in combination with short ultrasonic treatment. The obtained polysaccharide preparations were characterized by yield, chemical composition, and structural features, and the antioxidant activity of the water-soluble preparations tested. The results showed that the use of ultrasound at a reduced extraction time of 10 min as compared to 60 min of the classical procedure, with a 5% NaOH solution, resulted in the greatest yield of hemicelluloses. The AOA of their water-soluble portion ranged between 48 and 80%, indicating the antioxidant potential of these materials. The xylan polymers isolated from both AS and ASR might serve as biopolymer sources in native form or after targeted modification for production of value-added substances and polysaccharide-based antioxidants applicable in food, cosmetics, and other areas.