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This work defines the crystallinity of cellulose I materials on a dry‐weight basis. Theoretical and experimental developments in X‐ray diffraction lead to a crystallinity determination method that is estimated to reach 1σ accuracies of better than 0.05 (crystallinity defined between 0 and 1). The method is based on Rietveld modelling, to resolve cellulose I Bragg peaks, and a standard truncated invariant integral. Corrections are derived to account for incoherent scattering, moisture content and other compositional deviations from pure cellulose. The experimental development uses X‐ray diffraction in transmission fibre geometry with two‐dimensional pattern Rietveld modelling, including a crystal‐orientation distribution function. The crystallinities of a few commercial cellulose I materials were determined with the aim of illustrating the applicability of the method.

As the most abundant biopolymer on Earth, cellulose is a key structural component of the plant cell wall. Cellulose is produced at the plasma membrane by cellulose synthase (CesA) complexes (CSCs), which are assembled in the endomembrane system and trafficked to the plasma membrane. While several proteins that affect CesA activity have been identified, components that regulate CSC assembly and trafficking remain unknown. Here we show that STELLO1 and 2 are Golgi-localized proteins that can interact with CesAs and control cellulose quantity. In the absence of STELLO function, the spatial distribution within the Golgi, secretion and activity of the CSCs are impaired indicating a central role of the STELLO proteins in CSC assembly. Point mutations in the predicted catalytic domains of the STELLO proteins indicate that they are glycosyltransferases facing the Golgi lumen. Hence, we have uncovered proteins that regulate CSC assembly in the plant Golgi apparatus.

Dynamic vapor sorption and thermoporometry probe complementary dimensions of water interaction with cellulose. While sorption is primarily sensitive to the first hydration layers, thermoporometry is primarily sensitive to the nanometric water-filled pores. In this article, these analytical techniques are detailed and applied to model mesoporous materials and to a wide spectrum of celluloses. Correlations between techniques are explored. In dynamic vapor sorption, celluloses present a general characteristic time of desorption. On the other hand, they present highly variable characteristic times of sorption, indicating that material-specific properties may be inferred from sorption kinetics. Regarding thermoporometry, the thermodynamics of ice melting in irregular pore shapes is introduced. Moreover, in our thermoporometry analysis with differential scanning calorimeter, freezing temperature is extended to -70°C, allowing pores smaller than a few nanometers to be measured. Nevertheless, several data corrections are required for accurate thermoporometry at this condition. Comparisons between techniques show that sorption hysteresis is positively correlated with wet porosity. The presented developments and results will guide future application of these techniques to probe water in celluloses.