Soybean phytoalexins

Welle, R. and Schroder, J., Expression cloning in Escherichia coli and preparative isolation of the reductase coacting with chalcone synthase during the key step in the biosynthesis of soybean phytoalexins. Arch. Biochem. Biophys., 293, 377, 1992. 

To test the validity of the bioassay itself we prepared a diet containing increasing amounts of rotenone, a compound derived from isoflavones and thus chemically not far removed from the soybean phytoalexins. Results in this case followed exactly the expected dose response curve (Table VII). Both survival and weight gain of larvae were drastically affected by increasing concentrations of rotenone. This experiment showed that the bioassay would be capable of detecting toxic effects of the phytoalexins on the soybean looper larvae, if such effects were acute. It showed also that the detoxification mechanisms in the soybean looper, a rather polyphagous insect, may permit it to adequately overcome the antibiotic effect of the isoflavonoid phytoalexins, but not that of the isoflavone rotenone. 

Fig. 29. Proposed biosynthetic pathway of the soybean phytoalexin, glyceollin I. Reprinted from Reference 49 with permission of Academic Press Inc.

Hart S V, Kogan M, Paxton J D 1983. Effect of soybean phytoalexins on the herbivorous insects Mexican bean beetle and soybean looper. J Chem Ecol 9 657-672... 

Other common phytoalexins in food materials are pisatin, cinnamylphenols, glyceolin, phaseolin [13401 -40-6] (14), and 5-deoxykieritol in peas, beans, soybeans, and lima beans viniferin in grapes momilactones and ory2alexins in rice a-tomatine in tomato lubimen in eggplant and capsidiol in green peppers. 

M. Pamiske, B. Ahiborn, and D. Werner, Isoflavonoid-inducible resistance to the phytoalexin glyceollin in. soybean rhizobia. J. Bacterial 173 2222 (1991). 

P. E. Schmidt, M. Pamiske, and D. Werner, Production of the phytoalexin glyceollin I by soybean root response to symbiotic and pathogenic infection. Bot. Acta. 105 18 (1992). 

Welle, R. et al.. Induced plant responses to pathogen attack. Analysis and heterologous expression of the key enzyme in the biosynthesis of phytoalexins in soybean Glycine max L. Merr. cv. Harosoy 63). Eur. J. Biochem., 196, 423, 1991. 

Welle, R. and Grisebach, H., Phytoalexin synthesis in soybean cells elicitor induction of reductase involved in biosynthesis of 6 -deoxychalcone. Arch. Biochem. Biophys., 272, 97, 1989. 

Schopfer, C.R. et al., Molecular characterization and functional expression of dihydroxypterocar-pan 6a-hydroxylase, an enzyme specific for pterocarpanoid phytoalexin biosynthesis in soybean... 

Biggs, D.R., Welle, R., and Grisebach, H., Intracellular localization of prenyltransferases of isoflavonoid phytoalexin biosynthesis in bean and soybean. Planta, 181, 244, 1990. 

FIGURE 8.6 Structure of the phytoalexin isoflavonoid pterocarpans, maackianin, and pisatin from garden pea, and the isoflavones daidzein and genistein from soybean. 

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. 

Takeuchi, Y., Yoshikawa, M., Takeba, G., Kunisuke, T., Shibata, D. Florino, O. (1990). Molecular cloning and ethylene induction of mRNA encoding a phytoalexin elicitor-releasing factor P-l,3-glu-canase, in soybean. Plant Physiology 93, 673-82. 

Sharp, J. K., Valent, B., and Albersheim, P. 1984. Purification and partial characterization of a P-glucan fragment that elicits phytoalexin accumulation in soybean. J. Biol. Chem. 259, 11312-11320... 

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,... 

A feature of some pterocarpan phytoalexins (e.g., pisatin and glyceollin of pea and soybean, respectively) is their hydroxylation at position 6a, a reaction catalyzed by a microsomal cytochrome P450 monooxygenase.49 50 A cDNA encoding this enzyme was recently characterized from elicited soybean cell cultures.51 The microsomal protein, expressed in yeast cells, catalyzed the stereoselective hydroxylation of (6a/ , lla/ )-3,9-dihydroxypterocarpan to its 6a-hydroxy derivative. It was also demonstrated that the enzyme expression is regulated at the transcriptional level.51... 

HAGMANN, M.-L., HELLER, W., GRISEBACH, H Induction of phytoalexin synthesis in soybean. Stereospecific 3,9-dihydroxypterocarpan 6a-hydroxylase from elicitor-induced soybean cell cultures. Eur. J.Biochem., 1984,142,127-131. 

KOCHS, G., GRISEBACH, H., Phytoalexin synthesis in soybean purification and reconstitution of cytochrome P450 3,9-dihydroxypterocarpan 6a-hydroxylase and separation from cytochrome P450 cinnamate 4-hydroxylase. Arch Biochem. Biophys., 1989,273,543-553. 

ZAHRINGER, U EBEL, J., MULHEIRN, L.J., LYNE, R.L., GRISEBACH, H., Induction of phytoalexin synthesis in soybean - dimethylallyl pyrophosphate trihydroxypterocarpan dimethylallyltransferase from elicitor-induced cotyledons. FEBSLett., 1979,101,90-92. 

WELLE, R., GRISEBACH, H., Properties and solubilization of the prenyltransferase of isoflavonoid phytoalexin biosynthesis in soybean. Phytochemistry, 1991,30,479-484. 

Metalaxyl is clearly fungicidal i n vitro to a variety of phycomycetous fungi. Its activity in vivo may also be enhanced by stimulation of host plant defenses including hypersensitive cell death (104), accumulation of phytoalexins such as glyceollin (121), and cal lose encasement of hyphae (122) after fungal infection of metalaxy1-treated soybeans. However, the mi vivo concentration of the compound in cell sap may be sufficient for fungitoxicity alone to account for its protective activity (123). 

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