Isoflavonoid are a group of secondary metabolites common to the leguminous plants that play a role in plant defense responses and nodulation. Isoflavones have a role in plant disease responses (Dixon 2001) of soybean to pathogen attack (Wegulo et al., 2005). They can be divided into aglycones and glycones. Aglycones isoflavones are without sugar moiety for example genistein, daidzein, glycitein, formononetin and biochanin A (Dixon 2004). Glycosidic isoflavone such as daidzin, genistin, glycitin, ononin etc. are often present in high levels in healthy plants (Murakami et al., 2014; Durango et al., 2018). Absidia coerulea and Absidia glauca transform genistein and biochanin A. As a result of glycosylation of genistein and biochanin A, genistin and sissotrin is obtained (Sordon et al., 2017). Biochanin A and genistein have fungicidal property (Rivera-Vargas et al., 1993). Lotus leaves produce a number of isoflavans a specific class of isoflavonoid as a defense response against pathogens (Lanot and Morris 2005). High concentration of isoflavonoid phytoalexins was detected when cultivars were infected with in Cercospora arachidicola than when they were infected with Puccinia arachidis (Edwards et al., 1995). Weidenborner and Jha (1994) studied the structural-activity of isoflavonoid in relation to antifungal activities and observed that the unreduced structure of isoflavones has less inhibitory effect on the growth of fungi whereas, reduced isoflavones i.e. isoflavans showed very weak activity.
The effect of soybean isoflavones on pathogenic fungi was studied to corelate the fungistatic activity to their composition and structure (Naim et al., 1974). Guo et al. (2011) concluded soybean isoflavones daidzein and genistein that are released in rhizosphere may act as allelochemicals when interaction takes place between root and soil microbial community depending on the duration of monocropping. Continuous monocropping of soybean led to change in the soil microbial community structure which resulted in change of rhizosphere isoflavones. Both the isoflavones can be easily degraded in soil. During the process of biodegradation, diadzein and genistein exerted an effect on soil microbes and subsequently changed the microbial community structure (Guo et al., 2011). The zoospores of Phytophthora sojae arechemotactically attracted to isoflavones genistein and daidzein that are released by soybean roots (Tyler et al., 1996). Isoflavone genistein, daidzein and glicitein glycosides in soybean inhibited growth of Trichoderma lignorum, Rhizoctonia solani, Fusarium oxysporum, Pythium spp., Rhizopus spp. and Sclerotium rolfsii (Naim et al., 1974). The fungicidal activity of isoflavones from soybean and chickpea has been studied and it was observed that isoflavones and isoflavanones are variable in their activity whereas, isoflavans are moderately active inhibitors of fungal growth (Kramer et al., 1984). Armillaria mellea, the fungal pathogen causing root rot is able to convert the antifungal compound genistein from leguminous plant into an intermediate metabolites (Curir et al., 2006). Isoflavonoids of the biochanin A series showed high antifungal activity, while genistein isoflavan and other isoflavan with two hydroxyl and one methoxy group were fungitoxic (Weidenborner et al., 1990). Elicitation of plants with fungal phytotoxin prior to infection resulted in higher levels of prenylated iso-flavones, especially phytoalexins luteone and wighteone and their different glycoconjugates in comparison to those observed in plants infected only with fungal spores (Wojakowska et al., 2015).
Genistein is a free aglycone and inhibits fungal infection and spread of plant disease (Formela et al., 2014). As signal molecules, sugars stimulated accumulation of isoflavones including genistein. Infection with hemibiotrophic fungus Fusarium oxysporum enhanced the synthesis of genistein, wighteone and luteone in cells of embryo axes of yellow lupin with high endogenous level of sucrose, glucose and fructose (Formela et al., 2014).
Soybean leaves on attack by bacterial pathogen accumulate isoflavone aglucones, isoflavone glucosides and glyceollin. Isoflavone aglycones and isoflavone conjugates are induced in soybean leaves not only by pathogens but also by foliar insect herbivory (Murakami et al., 2014). Conjugation of isoflavone in the plant cell is related to storage in the vacuole (Yu et al., 2000). Glyceollin inhibits the growth of soil-borne fungal pathogen Fusarium solani f. sp. glycines (Lozovaya et al., 2004). Infection with zoospores of the phytopathogenic oomycetes Phytophthora megasperma f .sp. glycinea race 1 resulted in accumulation of glyceollin l in soybean (Schmidt et al., 1992).
Isoflavonone production pave way for rice plants to enter into symbiotic relationship with rhizobia. The membrane component play a role in the interaction of symbiotic or pathogenic bacteria with their host organisms, the function of this membrane must usually be to serve as a permeability barrier to prevent the entry of noxious compound and at the same time to allow the influx of nutrient molecules (Nikaido 2003).
Isoflavone production affects rhizosphere structure of microbial community thereby affecting growth and health of plants.
See Part V (F) for further information ………
References:
Curir, P., Dolci, M., Corea, G., Galeotti, F. and Lanzotti, V. 2006 The Plant Antifungal Isoflavone Genistein is Metabolized by Armillaria mellea Vahl to give Non-fungitoxic Products. Plant Biosystem 140(2): 156 – 162
doi.org/10.1080/11263500600756363
Dixon, R. A. 2004 Phytoestrogens. Annu. Rev. Plant Biol. 55: 225 – 261
doi: 10.1146/annurev.arplant.55.031903.141729
Dixon, R. A. 2001 Natural Products and Plant Disease Resistance. Nature 411(6839): 843 -847
doi: 10.1038/35081178
Durango, D., Murillo, J., Echeverri, F., Escobar, G. and Quinones, W. 2018 Isoflavonoid Composition and Biological Activity Extracts from Soybean Seedlings Treated by Different Elicitors. An. Acad. Bras. Cienc. 90(2) [Sppl. 1]: Rio de Janeiro
doi.org/10.1590/0001-3765201820170785
Edwards, C., Strange, R. N. and Cole, D. L. 1995 Accumulation of Isoflavonoid Phytoalexins in Leaves of Arachis hypogaea Differing in Reaction to Rust (Puccinia arachidis) and Early Leafspot (Cercospora arachidicola). Plant Pathol. 44(3): 573 – 579
doi.org/10.1111/j.1365-3059.1995.tb01679.x
Formela, M., Samardakiewicz, S., Marczak, L., Nowak, W., Narozna, D., Bednarski, W., Kasprowicz-Maluski, A. and Morkunas, I. 2014 Effects of Endogenous Signals and Fusarium oxysporum on the Mechanism Regulating Genistein Synthesis and Accumulation in Yellow Lupine and their Impact on Plant Cell Cytoskeleton. Molecules 19(9): 13392 – 13421
doi: 10.3390/molecules190913392
Guo, Z., Kong, C-H., Wang, J-G. and Wang, Y-F. 2011 Rhizosphere Isoflavones (diadzein and genistein) Levels and their Relation to the Microbial Community Structure of Mono-Cropped Soybean Soil in Field and Controlled Conditions. Soil Biol. Biochem. 43(11): 2257 – 2264
doi: 10.1016/j.soilbio.2011.07.022
Kramer, R. P., Hindorf, H., Jha, H. C., Kallage, J. and Zilliken, F. 1984 Antifungal Activity of Soybean and Chickpea Isoflavonones and their Reduced Derivatives. Phytochem. 23(10): 2203 – 2205
doi.org/10.1016/S0031-9422(00)80520-8
Lanot, A. and Morris, P. 2005 Elicitation of Isoflavan Phytoalexins. In: “Lotus japonicus Handbook”. Marquez, A. J. (eds.). Springer, Dordrecht. Chapter 7.6: 355 – 361
doi: 10.1007/1-4020-3735-X_35
Lozovaya, V., Lygin, A. V., Zernova, O. V., Li, S., Hartman, G. L. and Widholm, J. M. 2004 Isoflavonoid Accumulation in Soybean Hairy Roots upon Treatment with Fusarium solani. Plant Physiol. Biochem. 42(7-8): 671 -679
doi: 10.1016/j.plaphy.2004.06.007
Murakami, S., Nakata, R., Aboshi, T., Yoshinaga, N., Teraishi, M., Okumoto, Y., Ishihara, A., Morisaka, H., Huffaker, A., Schmelz, E. and Mori, N. 2014 Insect-Induced Daidzein, Formononetin and their Conjugates in Soybean Leaves. Metabolites 4(3): 532-546
doi: 10.3390/metabo4030532
Naim, M., Gestetner, B., Zilkah, S., Birk, Y. and Bondi, A. 1974 Soybean Isoflavones Characterization, Determination and Antifungal Activity. J. Agric. Food Chem. 22(5): 806 – 810
doi: 10.1021/jf60195a031
Nikaido, H. 2003 Molecular Basis of Bacterial Outer Membrane Permeability Revisited. Microbiol. Mol. Biol. Rev. 67(4): 593 – 656
doi: 10.1128/mmbr.67.4.593-656.2003
Rivera-Vargas, L. I., Schmitthenner, A. F. and Graham, T. L. 1993 Soybean Flavonoid Effects on and Metabolism by Phytophthora sojae. Phytochem. 32(4): 851-857
doi.org/10.1016/0031-9422(93)85219-H
Schmidt, P. E., Parniske, M. and Werner, D. 1992 Production of the Phytoalexin Glyceollin l by Soybean Roots in Response to Symbiotic and Pathogenic Infection. Botanica Acta 105(1): 18 – 25
doi.org/10.1111/j.1438-8677.1992.tb00262.x
Sordon, S., Poplonski, J., Tronina, T. and Huszcza, E. 2017 Microbial Glycosylation of Daidzein, Genistein and Biochanin A: Two New Glucosides of Biochanin A. Molecules 22(1): 81
doi: 10.3390/molecules22010081
Tyler, B. M., Wu, M., Wang, J., Cheung, W. and Morris, P. F. 1996 Chemotactic Preferences and Strain Variation in the Response of Phytophthora sojae Zoospores to Host Isoflavones. Appl. Environ. Microbiol. 62(8): 2811 – 2817
doi: 10.1128/aem.62.8.2811-2817.1996
Wegulo, S. N., Yang, X-B., Martinson, C. A. and Murphy, P. A. 2005 Effects of Wounding and Inoculation with Sclerotinia sclerotiorum on Isoflavone Concentrations in Soybean. Can. J. Plant Sci. 85(4): 749 – 760
doi.org/10.4141/P04-076
Weidenborner, M. and Jha, H. C. 1994 Structure-activity Relationships among Isoflavonoids with Regard to their Antifungal Properties. Mycol. Res. 98(12): 1376 – 1378
doi.org/10.1016/S0953-7562(09)81066-6
Weidenborner, M., Hindorf, H., Jha, H. C., Tsotsonos, P. and Egge, H. 1990 Antifungal Activity of Isoflavonoids in Different Reduced Stages on Rhizoctonia solani and Sclerotium rolfsii. Phytochem. 29(3): 801 – 803
doi.org/10.1016/0031-9422(90)80022-9
Wojakowska, A., Kulak, K., Kachlicki, P. and Ski, S. S. 2015 Metabolic Response of Narrow Leaf Lupine (Lupinus angustifolius) Plants to Elicitation and Infection with Colletotrichum lupini under Field Conditions. Acta Physiologiae Plantarum 37(8): 152
doi: 10.1007/s11738-015-1896-6
Yu, O., Jung, W., Shi, J., Croes, R. A., Fader, G. M., McGoingle, B. and Odell, J. T. 2000 Production of the Isoflavones Genistein and Daidzein in Non-Legume Dicot and Monocot Tissues. Plant Physiol. 124(2): 781- 794
doi.org/10.1104/pp.124.2.781
BIOLOGICAL PROCESSES- A NATURE'S GIFT 