Alan Darvill

3-deoxy-d-lyxo-2-heptulosaric acid, a component of the plant cell-wall polysaccharide rhamnogalacturonan-II☆☆☆

Abstract 3-Deoxy- d - lyxo -heptulosaric acid (DHA) has been identified as a component of plant cell walls. This sugar was found in the pectic polysaccharide rhmanogalacturonan-II as a component of the disaccharide β- l -Ara f -(1→5)- d -DHA p . The structural formula and linkage position of DHA were determined by mass spectrometry of several derivatives. The lyxo configuration was determined by 1 H-n.m.r. spectroscopy of a derivative of the isolated disaccharide. The d configuration was determined by partial degradation of DHA to l -glyceric acid. DHA was found to be present in the primary cell walls of many higher plants, including several dicots, two monocots, and a gymnosperm, but was not detected in two bacterial lipopolysaccharides.

Structural features of the plant cell-wall polysaccharide rhamnogalacturonan-II

Abstract Rhamnogalacturonan-II (RG-II), isolated from the cell walls of suspension-cultured sycamore cells, has been further characterized. End-group analysis of RG-II showed that the polysaccharide contains about 30 glycosyl residues. Some 28 residues have been found as constituents of well characterized oligosaccharide fragments of RG-II. RG-II was treated with lithium metal dissolved in ethylenediamine to degrade the glycosyluronic acid residues. The major product was isolated, characterized, and shown to be the triglycosylalditol α-Xyl-(1→3)-α-Fuc-(1→4)-β-Rha-(1→3 1 )-apiitol. This tetrasaccharide fragment of RG-II has three residues in common with a previously characterized heptasaccharide that had been derived from RG-II by partial hydrolysis with acid. RG-II was found to contain a large number of branched galactosyluronic acid residues that have not yet been identified as components of oligosaccharide fragments, although they are undoubtedly part of an octa(galactosyluronic acid) fragment generated by partial acid hydrolysis. The results of sequential partial acid hydrolysis provided evidence that, in RG-II, the extremely acid-labile 3-deoxy- d - manno -2-octulosonic-acid and 3-deoxy- d - lyxo -2-heptulosaric acid residues are attached to O-3 of 3,4-linked galactosyluronic acid residues, and that the mildly acid-labile apiofuranosyl residues are attached to O-2 of 2,4-linked galactosyluronic acid residues. These and previously published data suggested that RG-II has a highly branched structure, arranged around an α-(1→4)-linked galactosyluronic acid backbone.

Structure and function of complex carbohydrates active in regulating plant-microbe interactions

A key regulatory role of complex carbohydrates in the interactions between plants and microbes has been estab— lished. The complex carbohydrates act as regulatory mole— cules or hormones in that the carbohydrates induce de novo protein synthesis in receptive cells. [11 The first complex carbohydrate recognized to possess such regulatory proper— ties is a polysaccharide (PS) present in the walls of fungi (2). Hormonal concentrations of this PS elicit plant cells to accumulate phytoalexins (antibiotics). [2] More recently we have recognized that a PS in the walls of growing plant cells also elicits phytoalexin accumulation; microbes and viruses may cause the release of active fragments of this endogenous elicitor. [3] Another PS in plant cell walls is the Proteinase Inhibitor Inducing Factor (PIIF) (53). This hormone appears to protect plants by inducing synthesis in plants of proteins which specifically inhibit digestive enzymes of insects and bacteria. [4] Glycoproteins secreted by incompatible races (races that do not infect the plant) of a fungal pathogen of soybeans protect seedlings from attack by compatible races. Glycoproteins from compatible races do not protect the seedlings (61). [5] The acidic PS secreted by the nitrogen—fixing rhizobia appear to function in the infection of legumes by the rhizobia. W.D. Bauer and his co—workers have evidence that these PS are required for the development of root hairs capable of being infected by symbiont rhizobia. Current knowledge of the structures of these biologically active complex carbohydrates will be presented.

A fluorescence assay for enzymes that cleave glycosidic linkages to produce reducing sugars

A rapid, facile, and sensitive assay has been developed for enzymes that generate reducing sugars. The assay is a modification of a method for post-HPLC column derivatization and detection of reducing sugars and is carried out in a single test tube. The assay is useful for large numbers of samples, such as those produced during purification of enzymes. Less than 500 pmol of reducing sugar can be quantitatively measured. The assay reported here is at least 10 times more sensitive than either the commonly employed parahydroxybenzoic acid hydrazide method or the recently reported bicinchoninate method, and 50 times more sensitive than the Nelson-Somogyi method.