Plant cell walls role in biofuels

An article published this year similar to the one we have read in class has discussed the major fuel production processes for attaining fuel from cell walls. It describes the method which entails degradation of polysaccharides in lignocellulosic feedstock to monosaccharides and their subsequent fermentation to ethanol or other advanced biofuels. The major challenge here is that plants have eveolved wall structures that are recalcigtrant to biological degradation, so one major research objective of plant scientists is to make walls more open and accessible to enzymatic degradation.  Yeast and bacterial strains have also been used to produce fuel by the fermentation of pentoses, but they are not very efficient.  One desirable change is an increased abundance of hexose-containing polymers such as cellulose or mannans rather than xylans.  Lastly, they discuss an alternative way to produce fuels by the combustion and gasification of lignocellulosic to syngas (a mixture of CO,CO2, and H2 gas) that can be transformed into ethanol by microbes.

Interestingly, the authors also discussed some changes in cell walls due to environmental responses. For example, as a response to mechanical stresses such as wind or changes in gravitational stimuli, trees can develop specialized tissues known as reaction wood, and this type of wood enables the return of stems back to a vertical position. Another example of distinct wall structure made by a plant cell is the papilla formed at the site where a pathogenic fungus attempts to penetrate a plant. A papilla, a multi-layered wall structure containing callose, lignin, and other structural proteins, are produced as a result of the plant cell’s sensing mechanism triggered by invading pathogens.  These examples suggest that plant cell are able to undergo reprogramming of their wall biosynthetic machinery and understanding this will enable rational changes of cell wall composition that will allow enhanced biofuel production.  A news article, however, had some some light on this field by the grass, Brachypodium distachyon. This plant can be used as a model organism that is similar to but easier to grow and study than important agricultural crops, including wheat and barley.  A major stumbling block in using switchgrass or any perennial grass as a biofuel crop is the difficulty in breaking down its cell walls, an essential step in producing ethanol from cellulosic biomass. Brachypodium may hold the key to finding ways to produce plant cell walls that are easy to break down, which is precisely what many researchers are hoping for.

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