Dehydration-induced physical strains of cellulose microfibrils in plant cell walls

The effect of dehydration of plant cell walls on the physical status of cellulose microfibrils (CMFs) interspersed in pectin matrices was studied. Vibrational sum frequency generation (SFG) spectroscopy analysis of cellulose revealed reversible changes in spectral features upon dehydration and rehydration of onion epidermal walls used as a model primary cell wall (PCW). Combined with microscopic imaging and indentation modulus data, such changes could be attributed to local strains in CMFs due to the collapse of the pectin matrix upon dehydration. X-ray diffraction (XRD) showed that the (200) spacing of cellulose in dried PCWs is larger than that of cellulose Iβ obtained from tunicates. Thus, the modulus of CMFs in PCWs would be lower than those of highly-crystalline cellulose Iβ and inhomogeneous local bending or strain of CMFs could occur readily during the physical collapse of pectin matrix due to dehydration.