Cellulose constitutes the main scaffold of plant cell walls, but its structure has long been elusive because of the low crystallinity of plant cellulose compared to bacterial and algal cellulose and the significant interactions of cellulose with matrix polysaccharides in plant cell walls. By 13C labeling of primary cell walls and employing high-field two-dimensional 13C-13C correlation NMR, we have obtained highly resolved 2D spectra that reveal the presence of 5 different interior cellulose conformations and at least 2 different types of surface cellulose 1. These polymorphs have distinct 13C chemical shifts, which differ from the chemical shifts of bacterial and algal cellulose. By correlating the chemical shifts between different polymorphs and with the chemical shifts of matrix polysaccharides, and by assessing water accessibility, we have identified the locations of these polymorphs in the microfibril. The resulting model of a conformationally heterogeneous microfibril is in excellent agreement with quantitative 13C NMR spectra that indicate at least 24 glucan chains in the primary wall cellulose microfibril 2. This cellulose structural polymorphism is found in both dicot and grass primary cell walls, suggesting its chief origin as the interactions of cellulose with matrix polysaccharides in the wall. Our studies of the primary cell walls of seedlings of model plants showed that cellulose and pectins contact with each other on the molecular scale 2. We recently conducted a structural study of the cell walls of the flowering tissues, or inflorescence, of Arabidopsis. Interestingly, the faster growing regions of inflorescence show higher pectin content, higher hydration, and weaker cellulose-pectin interactions, indicating that weakening cellulose-pectin interactions causes cell wall expansion. This finding highlights the importance of cellulose-pectin interactions for the structural integrity and rigidity of the cell wall.

Polymorphic structures and pectin interactions of cellulose in primary plant cell walls from multidimensional solid-state NMR

253rd National Meeting (2017)

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