The metabolism of carbohydrates underpins some of the most fundamentally important processes in nature. The diverse structure and function of glycans is reflected in the vast array of enzymes involved in their synthesis (glycosyltransferases), modification (carbohydrate esterases and methyl transferases) and breakdown (glycoside hydrolases and polysaccharide lyases). However, our knowledge of plant cell wall structure and metabolism is still rather limited (Somerville et al. 2004). Even with the advent of genome sequencing, we are still confounded by the apparent wealth of genes for which no specific functional assignment can be made. Developments in informatics (Henrissat et al. 2001) have allowed us to dissect the 25498 genes present in the genome of Arabidopsis thaliana (Walbot 2000) such that more than 420 genes have been assigned probable roles in pathways responsible for the synthesis and modification of cell wall polymers (Arabidopsis Genome Initiative 2000). The high degree of apparent redundancy evident from such analyses may well reflect subtle differences in enzyme substrate specificity.
The need for new tools with which to dissect plant polysaccharide metabolism is clearly evident. At one level, such tools may come from molecular biology and genetics. However, in contrast to DNA, RNA and protein sequences, which are template-encoded, the structure of oligo- and polysac-charides is not directly genome-dependent in the same predictable fashion (Turnbull & Field 2007) . For the foreseeable future, genomic information may therefore be less influential in glycobiology than elsewhere. Particularly in relation to plant cell wall research, the need for direct analysis of glycan structure and enzyme function is clear. Paying specific attention to pectic polysaccharides, this chapter addresses the opportunities and challenges that need to be addressed in the preparation of oligosaccharide probes that might find application in structural and biosynthetic studies.
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