Polysaccharides, elicitors

Among the polysaccharide elicitors are 3,6-3-glucans from Phytophthora megasperma (84, 85) and yeast cell walls (59) and the algal glucan, laminarin (84)., which have structures comparable to those described for the wilt-inducing P. cinnamomi,... 

Soybean cotyledons require eui exogenous stimulus for the synthesis of the isoflavonoid phytoalexin glyceollln and its structural Isomers. The polysaccharide elicitor from the fungal pathogen Pms is a highly active Inducer of glyceollln synthesis in a model system utilizing wounded soybean cotyledons. 

To increase production and facilitate isolation, plant cells have been immobilised on various matrices such as polyurethane foam and calcium alginate gel beads,24 while elicitation (i.e. the induction of a defence response) is generally critical for the production of secondary metabolites. The rationale for the use of elicitors is that plants produce secondary metabolites as part of a defence response to stress, either biotic (pathogen infection) or abiotic (ultraviolet, toxic heavy metals and rare earth ions). Jasmonic acid plays a crucial role in plant stress responses and, along with fungal polysaccharides and heavy metals, is the most widely employed elicitor in plant tissue cultures.30... 

Robertson, D., McCormack, B.A., and Bolwell, G.P., 1995, Cell wall polysaccharide and related metabolism in elicitor-stressed cells of French bean (Phaseolus vulgaris L.). Biochem. J. 306 745-750. 

Of special interest are the polysaccharides that act as elicitors. Various heterogeneous polymers obtained from fungal and bacterial cell walls also act as elicitors. These include extracellular polysaccharides, lipoprotein polysaccharides, and glycoproteins. 

The production of phytoalexins in response to microbes requires a mechanism which enables the plant to recognize the invading organism and subsequently leads to the stimulation of phytoalexin synthesis at the site of microbial penetration. Substances of microbial origin which mediate phytoalexin accumulation in plants have been called elicitors(Ref. 2) and it has been shown in several cases that the culture medium of pathogens contained components which elicited phytoalexin accumulation in the pathogen s host (Ref. 3). Studies on the nature of elicitors have resulted in the partial purification and characterization of a number of molecules from different microbial sources. Elicitors have been reported to have a dependence for activity on a polypeptide or protein (Ref. 4), a glycoprotein (Ref. 5), or polysaccharide (Ref. 6) component. 

Hahn, M. G., A. G. Darvill, and P. Albersheim, Host-pathogen interactions. XIX. The endogenous elicitor, a fragment of a plant cell wall polysaccharide that elicits phytoalexin accumulation in soybeans. Plant Physiol., 68, 1161-1169 (1981). 

Grapevine cells also respond to the presence of polysaccharides. For example, when laminarin, which is a p-1,3 glucan derived from the brown algae Laminaria digitata, was used as elicitor in V. vinifera cv Gamay cells, 65 pg trans-R FW was accumulated in the culture medium after 8 h of treatment [44]. s-viniferin was present predominantly inside the cells, where it peaked (130 pg g FW) after 20 h, although a significant amount of s-viniferin (62 pg g FW) was also detected after 12 h in the extracellular medium [44]. 

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