The Spatial Orientation and Interaction of Cell Wall Polymers in Bamboo Revealed with a Combination of Imaging Polarized FTIR and Directional Chemical Removal

The mechanical and physical properties of lignocellulosic materials are closely related to the orientation and interaction of the polymers within cell walls. In this work, Imaging Polarized FTIR, combined with directional chemical removal, was applied to characterize the spatial orientation and interaction of cell wall polymers in bamboo fibers and parenchyma cells from two bamboo species. The results demonstrate the cellulose in bamboo fibers is nearly axially oriented whereas it is almost transversely arranged in parenchyma cells. Xylan and lignin are both preferentially oriented alongside cellulose, but with less orientation degre in the parenchyma cells. After lignin removal, the average orientation of xylan and cellulose is little affected, suggesting a strong interaction between cellulose and xylan. Meanwhile, the alkaline treatment significantly weakens the orientation of lignin in both fibers and parenchyma cells, and more significant for the latter, indicating the easy-degradable nature of lignin in parenchyma cells. And, it seemed the lignin and xylan in fibers were more difficult to be removed as compared to parenchyma cells, supporting the assumption that stronger interaction exists between lignin and xylan in the fibers. In a word, it was believed parenchyma cells are more suitable for biorefinery owing to its less ordered and relatively loose molecular assembly, as compared to fibers.

The Placenta of Physcomitrium patens: Transfer Cell Wall Polymers Compared across the Three Bryophyte Groups

Following similar studies of cell wall constituents in the placenta of Phaeoceros and Marchantia, we conducted immunogold labeling TEM studies of Physcomitrium patens to determine the composition of cell wall polymers in transfer cells on both sides of the placenta. Sixteen monoclonal antibodies were used to localize cell wall epitopes in the basal walls and wall ingrowths in this moss. In general, placental transfer cell walls of P. patens contained fewer pectins and far fewer arabinogalactan proteins AGPs than those of the hornwort and liverwort. P. patens also lacked the differential labeling that is pronounced between generations in the other bryophytes. In contrast, transfer cell walls on either side of the placenta of P. patens were relatively similar in composition, with slight variation in homogalacturonan HG pectins. Compositional similarities between wall ingrowths and primary cell walls in P. patens suggest that wall ingrowths may simply be extensions of the primary cell wall. Considerable variability in occurrence, abundance, and types of polymers among the three bryophytes and between the two generations suggested that similarity in function and morphology of cell walls does not require a common cell wall composition. We propose that the specific developmental and life history traits of these plants may provide even more important clues in understanding the basis for these differences. This study significantly builds on our knowledge of cell wall composition in bryophytes in general and in transfer cells across plants.

Sequential Deposition and Remodeling of Cell Wall Polymers During Tomato Pollen Development

The cell wall of a mature pollen grain is a highly specialized, multilayered structure. The outer, sporopollenin-based exine provides protection and support to the pollen grain, while the inner intine, composed primarily of cellulose, is important for pollen germination. The formation of the mature pollen grain wall takes place within the anther with contributions of cell wall material from both the developing pollen grain as well as the surrounding cells of the tapetum. The process of wall development is complex; multiple cell wall polymers are deposited, some transiently, in a controlled sequence of events. Tomato (Solanum lycopersicum) is an important agricultural crop, which requires successful fertilization for fruit production as do many other members of the Solanaceae family. Despite the importance of pollen development for tomato, little is known about the detailed pollen gain wall developmental process. Here, we describe the structure of the tomato pollen wall and establish a developmental timeline of its formation. Mature tomato pollen is released from the anther in a dehydrated state and is tricolpate, with three long apertures without overlaying exine from which the pollen tube may emerge. Using histology and immunostaining, we determined the order in which key cell wall polymers were deposited with respect to overall pollen and anther development. Pollen development began in young flower buds when the premeiotic microspore mother cells (MMCs) began losing their cellulose primary cell wall. Following meiosis, the still conjoined microspores progressed to the tetrad stage characterized by a temporary, thick callose wall. Breakdown of the callose wall released the individual early microspores. Exine deposition began with the secretion of the sporopollenin foot layer. At the late microspore stage, exine deposition was completed and the tapetum degenerated. The pollen underwent mitosis to produce bicellular pollen; at which point, intine formation began, continuing through to pollen maturation. The entire cell wall development process was also punctuated by dynamic changes in pectin composition, particularly changes in methyl-esterified and de-methyl-esterified homogalacturonan.

Cell wall polymers in the Phaeoceros placenta reflect developmental and functional differences across generations

The placenta of hornworts is unique among bryophytes in the restriction of transfer cells that are characterized by elaborate wall labyrinths to the gametophyte generation. During development, cells around the periphery of the sporophyte foot elongate, forming smooth-walled haustorial cells that interdigitate with gametophyte cells. Using immunogold labeling with 22 antibodies to diverse cell wall polymers, we examined compositional differences in the developmentally and morphologically distinct cell walls of gametophyte transfer cells and sporophyte haustorial cells in the placenta of Phaeoceros. As detected by Calcofluor White fluorescence, cellulose forms the cell wall scaffolding in cells on both sides of the placenta. Homogalacturonan (HG) and rhamnogalacturonan I (RG-I) pectins are abundant in both cell types, and haustorial cells are further enriched in methyl-esterified HGs. The abundance of pectins in placental cell walls is consistent with the postulated roles of these polymers in cell wall porosity and in maintaining an acidic apoplastic pH favorable to solute transport. Xyloglucan hemicellulose, but not mannans or glucuronoxylans, are present in cell walls at the interface between the two generations with a lower density in gametophytic wall ingrowths. Arabinogalactan proteins (AGPs) are diverse along the plasmalemma of placental cells and are absent in surrounding cells in both generations. AGPs in placental cell walls may play a role in calcium binding and release associated with signal transduction as has been speculated for these glycoproteins in other plants. Callose is restricted to thin areas in cell walls of gametophyte transfer cells. In contrast to studies of transfer cells in other systems, no reaction to the JIM12 antibody against extensin was observed in Phaeoceros.

Effect of Exogenous Auxin Treatment on Cell Wall Polymers of Strawberry Fruit

The role of auxin in the fruit-ripening process during the early developmental stages of commercial strawberry fruits (Fragaria x ananassa) has been previously described, with auxin production occurring in achenes and moving to the receptacle. Additionally, fruit softening is a consequence of the depolymerization and solubilization of cell wall components produced by the action of a group of proteins and enzymes. The aim of this study was to compare the effect of exogenous auxin treatment on the physiological properties of the cell wall-associated polysaccharide contents of strawberry fruits. We combined thermogravimetric (TG) analysis with analyses of the mRNA abundance, enzymatic activity, and physiological characteristics related to the cell wall. The samples did not show a change in fruit firmness at 48 h post-treatment; by contrast, we showed changes in the cell wall stability based on TG and differential thermogravimetric (DTG) analysis curves. Less degradation of the cell wall polymers was observed after auxin treatment at 48 h post-treatment. The results of our study indicate that auxin treatment delays the cell wall disassembly process in strawberries.

Evolution of Fungal Carbohydrate-Active Enzyme Portfolios and Adaptation to Plant Cell-Wall Polymers

The postindustrial era is currently facing two ecological challenges. First, the rise in global temperature, mostly caused by the accumulation of carbon dioxide (CO2) in the atmosphere, and second, the inability of the environment to absorb the waste of human activities. Fungi are valuable levers for both a reduction in CO2 emissions, and the improvement of a circular economy with the optimized valorization of plant waste and biomass. Soil fungi may promote plant growth and thereby increase CO2 assimilation via photosynthesis or, conversely, they may prompt the decomposition of dead organic matter, and thereby contribute to CO2 emissions. The strategies that fungi use to cope with plant-cell-wall polymers and access the saccharides that they use as a carbon source largely rely on the secretion of carbohydrate-active enzymes (CAZymes). In the past few years, comparative genomics and phylogenomics coupled with the functional characterization of CAZymes significantly improved the understanding of their evolution in fungal genomes, providing a framework for the design of nature-inspired enzymatic catalysts. Here, we provide an overview of the diversity of CAZyme enzymatic systems employed by fungi that exhibit different substrate preferences, different ecologies, or belong to different taxonomical groups for lignocellulose degradation.

Effect of Exogenously Applied 24-Epibrassinolide and Brassinazole on Xylogenesis and Microdistribution of Cell Wall Polymers in Leucaena leucocephala (Lam) De Wit

Plant growth regulators play a key role in cell wall structure and chemistry of woody plants. Understanding of these regulatory signals is important in advanced research on wood quality improvement in trees. The present study is aimed to investigate the influence of exogenous application of 24-epibrassinolide (EBR) and brassinosteroid inhibitor, brassinazole (BRZ) on wood formation and spatial distribution of cell wall polymers in the xylem tissue of Leucaena leucocephala using light and immuno electron microscopy methods. Brassinazole caused a decrease in cambial activity, xylem differentiation, length and width of fibres, vessel element width and radial extent of xylem suggesting brassinosteroid inhibition has a concomitant impact on cell elongation, expansion and secondary wall deposition. Histochemical studies of 24-epibrassinolide treated plants showed an increase in syringyl lignin content in the xylem cell walls. Fluorescence microscopy and transmission electron microscopy studies revealed the inhomogenous pattern of lignin distribution in the cell corners and middle lamellae region of BRZ treated plants. Immunolocalization studies using LM10 and LM 11 antibodies have shown a drastic change in the micro-distribution pattern of less substituted and highly substituted xylans in the xylem fibres of plants treated with EBR and BRZ. In conclusion, present study demonstrates an important role of brassinosteroid in plant development through regulating xylogenesis and cell wall chemistry in higher plants.