Cell wall structural foundations: Molecular basis for improving forage digestibilities

Forages play an important role in the world wide animal industry. The fiber (cell wall) portion makes up 300 to 800 mu g g(-1) of forage dry matter and represents a major source of nutritional energy for ruminants, but, unfortunately, less than 50% of this fraction is readily digested and utilized by the animal. Significant progress has been made in the past 30 to 40 yr towards understanding cell wall structure and function and developing mechanistic models that explain limitations to structural polysaccharide degradation and utilization by ruminants, In grasses, it is now clear that wall bound ferulates play a key role in cross-linking xylans to each other and to lignin, resulting in less degradable walls. Much has been accomplished in advancing our understanding of the lignification process in plants, particularly the genes and enzymes involved in the monolignol biosynthesis. The application of molecular techniques to this area has advanced our under standing of the metabolic process while pro riding tools for further exploration of wall structure and function and providing direction as to possible avenues to improve forage digestibility.