To better understand how hydrothermal pretreatment reduces plant cell wall recalcitrance, we applied a high throughput approach ("glycome profiling") using a comprehensive suite of plant glycan-directed monoclonal antibodies to monitor structural/extractability changes in Populus biomass. The results of glycome profiling studies were verified by immunolabeling using selected antibodies from the same toolkit. The array of monoclonal antibodies employed in these studies is large enough to monitor changes occurring in most plant cell wall polysaccharides. Results from these techniques demonstrate the sequence of structural changes that occur in plant cell walls during pretreatment-induced deconstruction, namely, the initial disruption of lignin-polysaccharide interactions in concert with a loss of pectins and arabinogalactans; this is followed by significant removal of xylans and xyloglucans. Additionally, this study also suggests that lignin content per se does not affect recalcitrance; instead, the integration of lignin and polysaccharides within cell walls, and their associations with one another, play a larger role.