Biology Reference
In-Depth Information
a grass that accumulates sucrose in high amounts (up to 20% in stems) and is
therefore an excellent source of biomaterial for bioethanol (
Karp and Shield,
2008
). Although the amount of sucrose found in sugarcane is exceptional as
compared to other grasses, it is because of their cell walls, in particular the
cellulose content, that grasses are thought tobe promising lignocellulosic biofuel
crops.
Grasses contain Type II cell walls, while most dicots have Type I cell walls.
The major polymer components of the cell wall are cellulose, arabinoxylans
and lignins. Cell walls of grasses are characterized by the high amount of
hydroxycinnamic acids, that is, ferulic acid (FA) and p-coumaric acid (pCA).
Lignin and phenolics bound to cell walls function counter-productively to
saccharification yield by reducing polysaccharide accessibility to degrading/
digestive enzymes. Further, the residual byproducts obtained from pretreat-
ments commonly used to reduce lignin content prior to saccharification for
bioethanol production may inhibit growth of microorganisms used during
fermentation. Therefore, genetic engineering to optimize lignin with desir-
able composition in plants dedicated for bioethanol production is a challenge
for the next decade. Interestingly, preliminary studies suggest that breeding
plants with a better yield for the biofuel production would positively impact
the animal feed production industry as cattle digestibility and artificial
saccharification yields are both affected by lignin content and composition
(
Vogel and Jung, 2001
).
The plants dedicated for biomass production are mainly C4 grasses that
under optimal environmental conditions demonstrate higher efficiency in
photosynthesis in addition to nutrient and water usage. It is possible to
distinguish biomass crops for biofuel production from those used for cattle
forage (
Karp and Shield, 2008
). The biofuel crops are mainly switchgrass
(Panicum virgatum) and miscanthus (Miscanthus sacchariflorus, Miscanthus
sinensis or Miscanthus giganteus) despite the fact that switchgrass also has
forage capacities. The C4 plants sorghum (Sorghum bicolour) and maize (Zea
mays) and C3 plants perennial ryegrass (Lolium perenne) and wheat (Triticum
aestivum) are considered as grain or/and forage crops and could be used
under certain conditions as biofuel crops. Noteworthy, some new species
with simple growth requirements, that is, Brachypodium distachyon and
Setaria viridis, have risen as model plants for grasses in addition to maize
(
Brkljacic et al., 2011; Brutnell et al., 2010; Doust et al., 2009; The
Brachypodium Initiative, 2010
).
In this chapter, work related to lignin deposition and biosynthesis in
grasses is reviewed. These processes vary as a consequence of several factors
including stage of development, tissue-type specificity and plant species. We
provide new data obtained from a newly created gene co-expression network
