lunes, 27 de diciembre de 2010

Researchers identify crucial transporters for lignin formation

Scientists at the United States Department of Energy’s Brookhaven National Laboratory identified a class of transporter molecules needed in lignin formation that will help them determine ways to better break lignin down for a more efficient biofuel production.

Lignin is an organic polymer that makes up the cell walls of a plant, giving it strength and form. The breakdown of lignin is a key component in producing biofuel from biomass because it allows producers to extract sugars in the cellulose.

However, this is also a major hurdle in the commercial availability of cellulosic biofuels. Because of lignin, it is very difficult to break down a plant’s cell wall and extract the needed sugars. Thus, Chang-Jun Liu, a biologist from the laboratory, and his colleagues are studying how lignin forms in order to understand better how to break it down.

“Being able to manipulate lignin biosynthesis would have a great influence on our ability to produce renewable biofuels from plant cellulosic feedstocks, and could also have a large effect on many other agricultural and industrial processes, such as the production of paper and more digestible foods for grazing animals,” explained Mr. Liu. 

The team detailed how the precursors to lignin called monolignols are transported across cellular membranes prior to linking up to the plant cell wall. The researchers believe that the transport process could provide a viable method to alter the lignin content.

Monolignols are made in the cell’s interior cytoplasm prior to cell wall construction. After they are created, they travel across the cellular membrane to either the cell’s vacuoles for storage or to the outer edge of the cell to link up to form the cell wall.

The research team isolated portions of cellular and vacuolar membranes and added pure monolignols and monolignol glucosides to the mix. They then observed that pure monolignols move mostly across the cellular membrane, while monolignol glucosides preferred to move towards the vacuoles.

But more importantly, they found that very little of either substance would move without the addition of adenosine triphosphate (ATP).

“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,” Mr. Liu explained.

To prove this point, the researchers added an agent that specifically inhibited ATP-binding cassette transporters and found that lignin refused to move through either membrane.

Now that the scientists have identified the class of transporters needed to bring monolignol to where it forms lignin, they will attempt to identify the specific elements 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,” Mr. Liu said.

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