Phytoalexins legumes

Akashi, T. et al., cDNA cloning and biochemical characterization of S-adenosyl-L-methionine 2,7,4 -trihydroxyisoflavanone 4 -0-methyltransferase, a critical enzyme of the legume isofiavonoid phytoalexin pathway. Plant Cell Physiol, 44, 103, 2003. 

The antiherbivory effects of phytoalexins have been studied in our laboratory using the Mexican bean beetle and the soybean looper (44). The Mexican bean beetle, Epilachna varivestis. is an oligophagous species that feeds preferentially on legume hosts. 

Table VIII. Effect of Legume Isoflavonoid Phytoalexins...

Many flavonoids are known to be phytoalexins, antiviral agents, and to serve as antiinflammatory and antitumor compounds. Several isoflavones have estrogenic activity in mammals (70). (-)-Vestitol and sativan, isoflavans from Lotus species, are phytoalexins. 3R(-)-Vestitol from the resistant pasture legume Lotus pedunculatus, has been demonstrated to be a feeding deterrent... 

Shimada N, Akashi T, Aoki T, Ayabe S. 2000. Induction of isoflavonoid pathway in the model legume Lotus japonicus Molecular characterization of enzymes involved in phytoalexin biosynthesis. Plant Sci 160 37-47. 

Dakora, F.D., Phillips, D.A. Diverse functions of isoflavonoids in legumes transcend anti-microbial definitions of phytoalexins. Physiol Mol Plant Pathol 1996 49 1-20. 

Secondly, the deacetylated form of chitin, chitosan, does not induce phytoalexin formation in the rice system but is active in other plant culture systems [99]. Glucan elicitors induce phytoalexins in legumes (soybean, chickpea, bean, alfalfa, pea) and solanaceous sp. (potato, sweet pepper) [100]. However, anthraquinone biosynthesis was stimulated in Morinda citrifolia by both chitin and chitosan. The degree of acetylation was found to be important in inducing defense responses. During the first few days of incubation after adding elicitor,... 

Recent progress has occurred In understanding the biochemistry that occurs In plant tissues treated with phytoalexin ellcitors. This work has been facilitated by the use of cloned plant genes encoding enzymes in phytoalexin biosynthetic pathways. Thus, In legumes. It... 

Although fungitoxlclty is the most characteristic biological property, phytoalexins may be antibacterial as well. Additionally, phytoalexins of legumes have been shown to be toxic to insects, while those from the sweet potato are poisonous to vertebrates (5J. 

Plant tissue culture is an extremely useful tool for investigating biochemical and hormonal aspects of plant metabolism. Such systems have been applied to studies of host-pathogen interactions and secondary metabolism. My laboratory has been investigating the biochemical regulation of phytoalexin accumulation in host-pathogen interactions of cultured legumes. 

Table II. Phytoalexin Concentrations in HgCl -stimulated Legume Callus Tissues (48 hours)...

Sativan, vestitol, 4-methoxy-maacklaln, lsovestltol, and l808atlvan were not detected in callus cultures derived from legumes that normally produce them. These phytoalexins may have been present at very low levels or were not elicited by mercuric chloride. 

Alternatively, chalcone reductase (CHR also known as deoxychalcone synthase) together with chalcone synthase and NADPH as a cofactor act in the formation of isoliquiritigenin, which is then isomerized, again by the enzyme chalcone isomerase, to form liquiritigenin, the precursor to daidzein, and the pterocarpan phytoalexins. A type II chalcone isomerase that seems to be found exclusively in the legumes catalyzes this isomerization reaction. Glycitein synthesis is not yet clearly defined, but is likely derived from liquiritigenin via flavonoid 6-hydroxylase, and an unidentified methyltransferase. 

Resveratrol (D 22.3.3) Phytoalexin of several legumes and of Vitis vinifera... 

Legume plants also contain many Hpophilic prenylated isoflavones (10-97), which are, in comparison with the original isoflavones, more efficient defence substances against pathogenic ilicitors (microorganisms) and animal pests (phytoalexins). They arise by prenylation of isoflavone precursors by dimethylallyl diphosphate. 

Pterocarpans are a group of modified isoflavonoids occurring in small amounts in legume plants (Fabaceae) and in several other families. They typically act as phytoalexins, protecting plants against pathogens. Unlike most of the isoflavones, pterocarpans are synthesised in response to biotic and abiotic stress factors. Their important precursors are the isoflavones daidzein and formononetin. 

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