Effect of humus acids on the mechanical properties of cell walls

Incubation of intact roots of Helianthus annuus I,. seedlings, root hairs of Trianea bogotensis Karst., cells and cell "ghosts" of Nitella syncarpa (Thuill) Chev. for 24 h in solutions of potassium humate (carbon content 100-150 mg/l) decreased the extensibility of cell walls and prevented the damage caused by calcium desorption from the cell surface. Incubation of young Nitella cells and root apexes of sunflower for 24 h in potassium humate solution (10-15 mg C/l) increased the extensibility of cell walls. A shift in the threshold of membrane excitation was found in Nitella cells, which indicates the adsorption of humus acids at the cell surface. It was suggested that humate increases cell wall extensibility indirectly, via reactions occurring in the protoplast. On the other hand, the hardening of cell walls is presumably due to the peroxydase-mediated dimerization of phenolic groups present in the humate and cell wall polymers.