A powerful new type of microscope, the 4Pi, has allowed scientists to see nanostructures inside of microscopic structures known as bordered pits within wood fiber cells. Previously, wood had to be dried, coated with carbon, and put under a high vacuum to be studied at the nanolevel. But the 4Pi, combined with an optical imaging technique called confocal laser scanning microscopy, makes it possible to see the wood cells in a more natural state, which has led to some interesting discoveries.
The team's research is featured as the cover story in the
The article, "A new approach for the study of the chemical composition of bordered pit membranes: 4Pi and confocal laser scanning microscopy," was written by
"The wood fiber cell, which is 100 times longer than it is wide, can be a quarter-inch long, or longer," said Goodell. Along each cell are hundreds of bordered pits, which are shared between the walls of adjacent wood fiber cells. A tree's fluid sap passes from one cell to the next through the bordered pits.
Each pit contains a mesh of nano-sized cellulose fibers that radiates out from a thickened, solid, central region called the torus -- looking somewhat like a bulls-eye in a target. Fluids ooze in through the mesh-like membrane, around the torus, and out the other side.
"When wood is injured, such as by an insect, or is being dried, like we do with kiln-dried lumber, the torus and part of the membrane will typically shift from the center of the pit to one side in order to seal the pit opening," he said.
The scientists have discovered how some of the nanostructures of the membrane move with the torus to seal off the pit. And they have found the location of certain chemical components of the membrane, which include crystalline cellulose and pectin.
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