The range of assays revealed that pure monolignols move across the cellular membrane while monolignol glucosides move preferentially into vacuoles. But most importantly, very little of either precursor would move across either type of membrane without the addition of ATP, the molecular "currency" for energy in cells.
"ATP is the energy molecule that is well known for providing the driving force for a group of transporters called ATP-binding cassette (ABC) transporters on cell membranes," Liu said.
To prove the point, adding an agent that specifically inhibits ABC transporters completely blocked uptake of lignin precursors by both types of membrane vesicles.
With these experiments and additional evidence, Liu and his colleagues demonstrated that ABC-like transporters on cell membranes are responsible for the transport of lignin precursors.
Now that the scientists have identified a class of transporters likely involved in sequestering and transporting lignin's building blocks, they'll pursue detailed studies to identify exactly which members of the class are involved.
"If we can identify those particular transporters we might be able to control their expression to reduce the precursor deposited into the cell wall, and thus lower the cell-wall content of lignin -or, selectively control the particular type of precursor deposited to change lignin composition and produce more easily cleavable biopolymers," Liu said.
|Contact: Karen McNulty Walsh|
DOE/Brookhaven National Laboratory