Elicitor-active structure

On the basis of our deductions with models, the observed structural requirements for optimum interaction of the active elicitor, hexa (E-D-glucopyranosyl)-D-glucitol, with DNA may be useful for the design of synthetic oligosaccharides and other nonobvious chemicals that exhibit elicitor activity. These requirements may be ... 

Syntheses of hexamers with structures (12) (component of the glycosphingolipid of a macrophage receptor, (13) (elicitor-active compound), (14) (ganglioceramide) and (15) (core of glycophosphatidyl inositol anchor of Trypanosoma brucci) have all been reported. 

As an exact analog of the phytoalexin elicitor branched heptasaccharide 82 the branched SPH 83 was devised with four amide bonds replacing the 1 -> 6 linkages of the pentasaccharide backbone and thus producing the same length. No elicitor activity was detected for 83, possibly because of the reduced flexibility or different conformation of the mimetic structure [56]. Mimetics of the sialyl Lewis and sialyl Lewis oligosaccharides have recently foimd increased attention. Baisch and... 

We can distinguish between secondary metabolites that are already present prior to an attack or wounding, so-called constitutive compounds, and others that are induced by these processes and made de novo. Inducing agents, which have been termed elicitors by phytopathologists, can be cell wall fragments of microbes, the plant itself, or many other chemical constituents (4,17,22-24). The induced compounds are called phytoalexins, which is merely a functional term, since these compounds often do not differ in structure from constitutive natural products. In another way this term is misleading, since it implies that the induced compound is only active in plant-microbe interactions, whereas in reality it often has multiple functions that include antimicrobial and antiherbivoral properties (see below). 

For some plant-elicitor systems, the structure of the molecules responsible for the induction have been determined and the receptors identified (327,328). But in the case of C. roseus, so far no elicitor molecules have been identified. Some synthetic oligosaccharides known as elicitors for some other plant species were not active in the C. roseus system (P. R. H. Moreno et at., unpublished results). When a P. megasperma elicitor preparation treated with trypsin was employed, the induction of DHBA and ajmalicine accumulation was not observed in C. roseus cells. This points to the presence of a glycoprotein as an active component (339). Considering the rather diverse reactions occurring after elicitor treatment, it cannot be excluded that several types of molecules are present in the crude elecitor preparations, which each have different effects. 

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