Ethephon-induced gummosis in sour cherry (Prunus cerasus L.). II. Flow characteristics of gum solutions

Flow of sour cherry (Prunus cerasus L. cv. Montmorency) gum solutions through a glass capillary was Newtonian for pressure gradients from 0 to 1.8 megapascals per meter, and hydraulic conductance was inversely proportional to solution viscosity in this range. However, flow became plastic at pressure gradients above 1.8 megapascals per meter, resulting in a decrease in solution viscosity. The magnitude of this effect diminished as gum concentration increased. Flow of water, a solution of the component sugar monomers of sour cherry gum, and sucrose solutions remained Newtonian over the entire pressure gradient range examined (0-4 megapascals per meter). Plastic flow of gum solutions in the vessels of intact sour cherry shoots is possible under pressure gradients induced by transpiration when high resistance to flow occurs over short distances.