Avenacin

CROMBIE, W.M.L., CROMBIE, L., Distribution of avenacins A-l, A-2, B-l and B-2 in oat roots Their fungicidal activity towards take-all fungus, Phytochemistry, 1986, 25, 2069-2073. 

OSBOURN, A.E., CLARKE, B.R., LUNNESS, P., SCOTT, P.R., DANIELS, M.J., An oat species lacking avenacin is susceptible to infection by Gaeumannomyces graminis var. tritici, Physiol. Mol. Plant Pathol., 1994, 45,457-467. 

Fig. 2.1 Strucnires of some common saponins. The strucnires of some of the saponins described in the text are shown, including aescin from horse chesnut, avenacin A-1 and avenacoside A from oat, and a-tomatine from tomato. The glucose molecule enclosed in square brackets in the structure of avenacoside A highlights the glucose moiety that is cleaved off by hydrolysis by glycosidases in disrupted oat leaf tissue, leading to the fungitoxic 26-desglucosyl avenacoside A. Redrawn from [94]...

Maizel JV et al (1964) Avenacin, an antimicrobial substance isolated from Avena saliva. I. Isolation and antimicrobial activity. Biochemistry 3 424... 

Armah CN et al (1999) The membrane-permeabrhzing effect of avenacin A-1 involves the reorganization of brlayer cholesterol. Biophys J 76 281... 

Fig. 1A-C. Examples of different classes of saponins A the triterpenoid saponin avenacin A-1 from roots of Avena spp B the steroidal saponin gracillin, from Costus speciosus C the steroidal glycoalkaloid a-tomatine from tomato (Lycopersicon spp.)...

Avenacinase, an enzyme from G. graminis var. avenae, is related to tomatinase from S. lycopersici because is able to deglucosilate tomatine by identical mode of action. However, the activity is very low and corresponds to approximately 2% of its activity towards avenacin A-1 [32]. Tomatinase form S. lycopersici, also can cleave avenacin A-l but has less than 0.01% of activity towards it in comparison to its activity towards tomatine [32]. Therefore, the two enzymes are highly specific for their respective host plant saponins. Purification and characterization of S. lycopersici tomatinase revealed that this enzyme shares many properties (including immunological cross-reactivity) with avenacinase... 

The structural relationship of tomatinase from B. cinerea to other tomatinases is unknown, but its molecular mass (70 kDa) is different from the other two enzymes mentioned before, 50 kDa from F. oxysporum [35, 38] and 110 kDa from S. lycopersici [33]. Moreover, when Quidde et al., attempted cloning of the tomatinase gene from B. cinerea using the tomatinase from S. lycopersici as a probe, they isolated a gene with high sequence homology, whose product had not tomatinase activity but was able to detoxify avenacin A-l [97], the saponin from oats related to some extent to tomatine. 

Burkhardt, H.J., Maizel, J. V., Mitchell, H.K. Avenacin, an antimicrobial substance isolated fromAvena sativa. II. Structure. Biochemistry 1964 3 426-431. 

Avenacin A-1 Avena sativa (oats) (Poaceae) Permeabilizes membranes... 

These crops possess constitutive allelochemicals that provide protection against attack by fungal pathogens. Graminaceous plants contain the hydrox-amic acids l,4-benzoxazin-3(4//)-ones DIMBOA (8.33) and DIBOA (8.34) and related benzoxazoles 8.35 and 8.36 which are stabilized as their glycosides. The roots of oats contain the triterpene avenacin (8.37) as an allelochemical. Various... 

The isolation of avenacins A-1, A-2, B-1 and B-2, chemical defences against cereal take-all disease. Structure of the aglycones, the avenestergenins and their anhydro dimers, M.J. Begley, L. Crombie, W.M.L. Crombie and D.A. Whiting, J. Chem. Soc., Perkin Trans 1, 1986, 1905. 

Pathogenicity of take-aH fungus to oats its relationship to the concentration and detoxification of the four avenacins, W.M.L. Crombie, L. Crombie, J.B. Green and J.A. Lucas, Phytochemistry, 1986, 25, 2075. 

When oat roots were used for bioassay, zoospores were first attracted and then caused lysis which raises the possibility that oat crops and their residues might be used to reduce soil populations of zoosporic plant pathogens. The cystospores were insensitive to concentrations of saponins or oat root extract that lysed zoospores. The zoospores lytic principle in oat root extract/exudate was believed to be a saponin, avenacin (61). The effects of avenacin (61) or root extracts on zoospores were identical to those of /0-aescin and consistent with a role of membrane active agents. Toxic effects of saponins on zoospores were also observed in Pseudoperonospora humuli Miyabe Takah. and Phytophthora spp. [139,140]. 

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