Cell wall preparation from A. thaliana hypocotyls. Schematic representation of the purification procedure of cell walls of A. thaliana etiolated hypocotyls. Sixteen g of fresh etiolated hypocotyls were ground. All supernatants were discarded after each centrifugation. The CW3 residue was extensively washed on a nylon net (25 μm pore size) with 3 L of 5 mM acetate buffer, pH 4.6. The CW4 pellet was ground in liquid nitrogen in a mortar with a pestle in order to reduce the size of the fragments, and lyophilized, obtaining 1.3 g of dry powder.