Structure‐activity relationships of biologically active oligosaccharides

Abstract

Oligosaccharides that exert biological effects on higher plants (other than as carbon or energy sources) have been termed 'oligosaccharins'. A limited number of specific oligo-fi-glucans derived from fungal cell walls exhibit oligosaccharin activity, at very low doses, switching on the synthesis of phytoalexins. The structural requirements for this biological activity are stringent, and there is strong evidence that the oligosaccharins of fungal origin act through a receptor in the plant cell membrane. Chemically unrelated oligosaccharins can also be produced by partial digestion of pectins and xyloglucans from higher plant cell walls. In some cases, for example, the a-L-fucosylated oligoxyloglucans that antagonise the growth-promoting effect of auxin, these plant-derived oligosaccharins have relatively strict structural requirements for activity and act at -lO^** mol m"-'; these may act via specific receptors. In other eases, for example, the growth-promoting action of other oligoxyloglucans, the stringency is somewhat lower and the activity is only seen at ~ lO""* mol m~'^, and these oligosaccharins are proposed to influence growth through their ability to modulate the activity of an enzyme, cellulase. A third class of plant-derived oligosaccharins, the oligo-a-galacturonides, appear to have much less stringent structural requirements; a number of unrelated physiological responses are evoked by the same range of oligo-a-galacturonides at -10^-* to 1 mol m"'^. We suggest that these oligosaccharins may act via a mechanism not involving a specific receptor, perhaps by interacting with the plasma membrane to bring about a change in its physical properties.

Rhamnogalacturonase B from Aspergillus aculeatus Is a Rhamnogalacturonan [alpha]-L-Rhamnopyranosyl-(1->4)-[alpha]-D-Galactopyranosyluronide Lyase

“…The discovery of new pectolytic enzymes like RG-lyase and, previously, RG-hydrolase (Schols et al, 1990a), RGacetylesterase (Searle-van Leeuwen et al, 1992), and RGrhamnohydrolase (Mutter et al, 1994) is very important with respect to the increasingly widely recognized function of polysaccharides as generators of signaling molecules, "oligosaccharins." There are indications that, in addition to homogalacturonic fragments, RG fragments are involved in plant processes, such as phytoalexin elicitation, wound signaling, hypersensitive response, morphogenesis, lignification, and ethylene synthesis (Aldington et al, 1991). The availability of well-characterized RG oligosaccharides, produced or modified by specific enzymes, will enable a more detailed investigation of the structure-activity relationships of these biologically active oligosaccharides.…”

Biochemical and morphological responses to abiotc elicitor chitin in suspension-cultured sugarcane cells

“…Besides lignification, other cellular alterations have been observed after the addition of biologically active substances to cell suspension cultures. Among these substances, some oligosacharides obtained from xiloglucans (McDougall and Fry, 1990;Joseleau et al, 1996), pectins (Aldington et al, 1991), chitin and chitosan (Peltonen et al, 1997) have been studied. Chitin, a cell wall polysaccharide from fungi, is an active elicitor of lignification in wounded wheat leaves and wheat suspension-cultured cells (Gotthardt and Grambow, 1992;Stacey and Shibuya, 1997;Shibuya and Minami, 2001;Ramonell al., 2002).…”

The potential physiological implications of polygalacturonic acid-mediated production of superoxide

“…[11][12][13][14][15] However, potential effects of PGA/OGA/PF on the activity of WAK1 or WAK2 have not been observed to date. We propose here that the specific property proposed by Aldington and co-workers, 8 is in fact the ability of the polymers of galacturonic acid (PGA/OGA/PF) to produce…”

“…7 However, the underlying mechanisms behind such processes are lacking. Aldington et al 8 have postulated that OGAs do not act through a receptor, but rather they owe their activity to some specific physical property. Pertinent to this is the fact that there is a broad range of active OGA structures.…”