3 ENZYMATIC DEGRADATION OF CELL WALL POLYSACCHARIDES

摘要

1 INTRODUCTION The plant cell wall represents the major source of carbohydrate polymers on the planet. Indeed it has been estimated that cellulose and hemicelluloses (in particular xylans) represent the two most abundant polysaccharides in nature. It is not surprising therefore that cell wall derived polysaccharides are commonly exploited for commercial means. Nature has generated a wide range of structural polysaccharides that are associated with the cell wall. Some of these can be exploited in their natural form but their functionality can often be enhanced by structural modifications. These modifications can be carried out post extraction of the polymers from the plant. Alternatively, understanding how the plant synthesizes and metabolises these polymers may lead to in planta methods for modification. The major in planta modifications are often associated with the degradation (or turnover) of the wall polymers during specific stages of plant growth and development. This chapter will firstly consider the general structure of the plant cell wall and the enzymatic capacities that result in degradation in planta. This will be followed by a more detailed consideration of the changes that can be brought about in the structure of pectin during fruit ripening. This provides an illustration of how modifications to cell wall degrading enzymes can result in changes in polymer structure.