Cheaper ethanol through more efficient production and stronger wood are two possibilities resulting from research by Erik E. Nielsen, Ph.D., adjunct professor of biology in Arts & Sciences. The discovery, published in a recent edition of The Journal of Cell Biology, sheds new light on how some complex sugars in plants are directed to the construction of cell walls.
“In plants, light energy is harvested to produce sugars, and some of these are processed into complex polymers for specific uses,” Nielsen said. “My team identified a distribution pathway for some of the complex sugars that are used in the construction of cell walls. This should help us understand how some of these building blocks of cell walls are delivered and how these building blocks are put together.”
Nielsen’s research is the first to identity some of the membrane trafficking steps in the deposition of cell wall components — a lightly researched area. His study is important because cotton, wood and other plant fibers that are vital to everyday life rely on the plant cell wall, which gives wood the strength needed for construction and furniture, among other uses, and cotton fibers the elasticity for use in cloth. The research could lead to crops with stalks that can be used to produce biofuels more efficiently and with less waste.
The paper’s novel scientific observation is the characterization of a membrane trafficking compartment believed to be involved in polar secretion of cell-wall components in plants.
“In the paper, we describe the identification of a cellular component that is essential for the proper targeting/delivery of secretory cargo to the tips of growing root-hair cells,” Nielsen said.
“Root-hair cells are a specific type of epidermal cell in roots that we have been using to monitor secretion pathways in plants. We use root-hair cells because during their development, they undergo a highly polarized expansion, in which deposition of new cell-wall components is restricted to the extreme tip of the growing root hair.”
Ethanol is produced by fermenting cellulose and other polysaccharides from plant cell walls or by fermenting starch from plant seeds. Fermenting starch from plant seeds is the preferred method because it is easier, but it is expensive because starch has other uses, such as food. Cellulose fermentation is not as efficient because the sugars in the cell wall are harder to release. In addition, other cell-wall components can interfere with the fermentation process.
“If we could modify the content of the plant cell wall, we may be able to produce plants whose cellulose and other cell-wall polysaccharides are more readily available for fermentation,” Nielsen said. “The other advantage if we could figure out how to make cellulosic ethanol fermentation work better is that these cell-wall sources — such as corn husks and stalks — are not really used for much else at present.”
Yet there are challenges in altering plant cell walls to make cellulose-based ethanol fermentation more efficient.
“A real problem is that we really don’t know much about how plant cell walls are put together,” Nielsen said. “While cellulose, the main load-bearing polysaccharide in plant cell walls, is synthesized at the plasma membrane, most of the other cell-wall polysaccharides and cell-wall proteins are synthesized and modified in the plant Golgi complex. These then have to somehow be delivered by membrane trafficking pathways to the correct places at the right times in order for normal plant cell growth and development to occur.”
Even the cellulose syntheses that make cellulose have to be sorted and delivered properly using membrane trafficking pathways. But Nielsen’s research offers a promising step.
“We really have no idea how all this sorting and packaging of cell-wall components is accomplished,” Nielsen said. “So what we’ve done with this research is to finally begin to characterize some of the compartments and membrane-trafficking pathways that are involved in cell-wall deposition.”