In situ analysis of grass cell wall polysaccharides

Plant cell walls are important resources of biomass and renewable energy. Miscanthus species are fast growing grasses that had been suggested to be potential bioenergy crops. Miscanthus x giganteus (M. x giganteus) grows faster and taller than its parents - M. sacchariflorus and M. sinensis. Wheat is the major food crop for human beings. Brachypodium distachyon is considered to be a model plant as it has a small genome size and rapid life cycle. In this study, cell wall polysaccharides in stems of the five grass species at different growth stages have been determined using an indirect immunofluorescence method with sets of specific monoclonal antibodies. Heteroxylan and mixed-linkage-glucan (MLG) epitopes are abundant in all grass species, but with different distributions in parenchyma regions and the detection levels of both polymers change during growth development. For M. x giganteus, pectic homogalacturonan (HG) epitopes were restricted to intercellular spaces of parenchyma and the high methylesterified LM20 HG epitope was strongly abundant in pith parenchyma cell walls. Some cell wall probes cannot access their target polymers because of masking by other polysaccharides. For all grass species in certain cell wall regions, the xyloglucan epitope is masked by heteroxylan, the pectic-galactan epitope is masked both by heteroxylan and MLG,and the LM2 AGP epitope is masked by pectin. These findings indicate the heterogeneity of polysaccharide distributions and molecular architectures in grasses, and this might be linked to grass anatomical and growth differences and may also be related to distinct cell wall functions between grass species. In summary, this fundamental knowledge of cell wall polysaccharide architectures in these important grass species will help us understand grass growth mechanisms, and may also be beneficial for the development of potential strategies for the efficient deconstruction of grass biomass that may make contribution to the biofuel industry.