Why don't trees 'bleed' when injured?

Professor Barry Goodell and his colleagues from the Virginia Agricultural Experiment Station; The Jackson Laboratory in Bar Harbor, Maine; and Georg-August University in Gottingen, Germany, discovered how “check valves” in wood cells control sap flow and protect trees when they are injured. Their work was featured on the cover of the American Journal of Botany. Thanks to a powerful new type of microscope, scientists can now see nanostructures in wood fiber cells in a more natural state.

A tree’s fluid sap passes from one cell to the next through nanostructures called bordered pits. Each pit contains a mesh of cellulose fibers that radiates out from a thickened, solid, central region called the torus — looking somewhat like a bull’s-eye in a target. Fluids ooze through the mesh- like membrane, around the torus, and out the other side.

The scientists have discovered how some of the nanostructures of the membrane move with the torus to seal off the pit when wood is damaged or is being dried, which helps explain how trees seal off their cells so that they don’t “bleed to death” or lose all their sap when they are injured.

Read the full press release.