Ronald J.F.J. Oomen

If Homogalacturonan Were a Side Chain of Rhamnogalacturonan I. Implications for Cell Wall Architecture

Pectin, an important cell wall component of dicotyledonous plants, is probably the most complex macromolecule in nature. Here, we critically summarize the large amount of data on pectin structure. An alternative model for the macromolecular structure of pectin is put forward, together with ideas on

Transcript imaging with cDNA-AFLP: a step by step protocol.

The method of cDNA-AFLP allows detection of differentially expressed transcripts using PCR. This report provides a detailed and updated protocol for the cDNA-AFLP procedure and an analysis of interactions between its various parameters. We studied the effects of PCR cycle number and template dilution level on the number of transcript derived fragments (TDFs). We also examined the use of magnetic beads to synthesise cDNA and the effect of MgCl2 concentration during amplification. Finally, we determined the detection level of the cDNA-AFLP method using TDFs of various sizes and composition. We could detect TDFs corresponding to a single copy per cell of a specific transcript in a cDNA-AFLP pattern, indicating high sensitivity of the method. Also, there was no correlation between concentration of detectable TDF and the fragment size, stressing the high stringency of the amplification reactions. Theoretical considerations and specific applications of the method are discussed.

Pectin — the Hairy Thing

Pectin is one of the most complex biomacromolecules in nature. In fact, it is a collection of different kinds of polysaccharides, which are most likely covalently connected to each other. In vitro degradation studies of pectic polysaccharides with novel fungal pectinases, investigations in which these polymers were treated with dilute acid, and microscopic analysis of extracted pectins have provided clues on how these polysaccharides are linked. These new findings have prompted us to believe that pectin is not an extended backbone consisting of homogalacturonan and rhamnogalacturonan regions, but rather a rhamnogalacturonan with neutral sugar and homogalacturonan side chains.

Remodelling pectin structure in potato

Figure options Download full-size image Download as PowerPoint slide Pectin is a collection of polysaccharides, which play an important role in controlling the pore size of the plant cell wall, regulating cell-cell adhesion, and providing a source of sig-nalling molecules that elicit a range of cellular responses. Apart from this, pectins are of interest because they are an attractive hydrocolloid for various food applications. The kind and distribution of decorative groups in the pectic molecules largely determines for which application a particular pectin is most suitable. After the extraction of starch from potato tubers, a by-product is obtained, which is relatively rich in pectin. However, the quality of these pectins is poor compared to that from other sources such as citrus and apple. Rather than trying to change the structural characteristics of potato pectin post-harvest, we have embarked on achieving this in the potato plant itself. This paper summarises the structural features of pectin, the distribution of various pectic epitopes in tuber cell walls, the enzymes involved in its biosynthesis and degradation, and strategies employed to alter its fine structure in planta.

Towards Unravelling the Biological Significance of the Individual Components of Pectic Hairy Regions in Plants

Highly branched pectins, which are comprised of a rhamnogalacturonan (RG I) backbone carrying galactan and arabinan side-chains, are generally referred to as hairy regions. Even though composition of the hairy regions has been well established in many plants, their biological function is still unknown. Developmental studies have already shown distinct antibody labelling patterns for the different epitopes present on the hairy region, suggesting that they may have different functions. This review compares the results from the developmental studies together with those from mutagenized and genetically modified plants with compositional alterations to the hairy region. In particular, the specific degradation of hairy regions, by the introduction of fungal enzymes in potato, enables the assignment of a putative biological function to the constituent polymers of the hairy region. We hypothesize that the most important function of the galactan hairs is to regulate the pore size of the cell wall. The deposition of galactan may restrict the access of modifying enzymes to the wall. In planta fragmentation of the RG I backbone shows severe histological modifications in potato tuber tissue. This suggests that the RG I backbone has an important function for normal potato tuber cell division and tissue development.