Simulation Study of the Water Ordering Effect of the β-(1,3)-Glucan Callose Biopolymer.

Callose, a polysaccharide closely related to cellulose, plays a crucial role in plant development and resistance to environmental stress. These functions are often attributed to the enhancement by callose of the mechanical properties of semiordered assemblies of cellulose nanofibers. A recent study, however, suggested that the enhancement of mechanical properties by callose might be due to its ability to order neighboring water molecules, resulting in the formation, up to room temperature, of solid-like water-callose domains. This hypothesis is tested by atomistic molecular dynamics simulations using ad hoc models consisting of callose and cellulose hydrogels. The simulation results, however, do not show significant crystallinity in the callose/water samples. Moreover, the computation of the Young's modulus gives nearly the same result in callose/water and in cellulose/water samples, leaving callose's ability to link cellulose nanofibers into networks as the most likely mechanism underlying the strengthening of the plant cell wall.