Disease resistance in plants depends on the activation of more than one biochemical pathway. The antimicrobial phytoalexins produced by Phaseolus vulgaris are the prenylated isoflavonoids kievitone and phaseollidin (Turbek et al., 1992).
Phaseollin and phaseollidin accumulated as a defense response in bean against the infection caused by Colletotrichum lindemuthianum. However, phaseollidin accumulated earlier than phaseollin and at greater concentration (Soriano-Richards et al., 1998). Phaseollin caused loss of electrolytes and betacyanin from beet root storage tissue and killed beet leaf protoplasts. The death of cell by phaseollin may result in loss of integrity of the tonoplast which allows the release of harmful plant metabolites or hydrolytic enzymes into cytoplasm (Hargreaves 1980). Bean plant response to nine different races of Pseudomonas syringae pv phaseolicola causing bacterial halo blight. The accumulation of isoflavonoid, phaseollin in bean restricted the bacterial growth (Bozkurt and Soylu 2011). Hypersensitive response in Phaseolus vulgaris was observed when leaf tissue was inoculated with pseudomonas phaseolicola which showed high concentration of isoflavonoid phytoalexins phaseollin (pterocarpan), phaseollinisoflavan (isoflavan) and kievitone (isoflavanone) (Gnanamanickam and Patil 1977).
Kievitone is an isoflavanone and occurs in hypocotyls of Phaseolus vulgaris L. infected with Rhizoctonia solani (Smith et al., 1973). It may contribute to disease resistance by restricting the spread of fungus Rhizoctonia solani in invaded tissue (Smith et al., 1975). High molecular weight cell wall component from Colletotrichum lindemuthianum elicited browning and phytoalexin accumulation. Kievitone was the main phytoalexin produced by the cotyledons (Theodorou and Smith 1979). The mycelial growth of Aphanomyces euteiches, Rhizoctonia solani and Fusarium solani f. sp. phaseoli was inhibited by kievitone (Smith 1976). Phaseollinisoflavan and kievitone are a strong bactericidal compound (Wyman and Van Etten 1978).
Neoflavonoids:
Neoflavonoid is a group of C-15 naturally occurring compounds which are related structurally and biogenetically to the flavonoids and to the isoflavonoids. Neoflavonoid is found in Guttiferae, the Papilionoideae (subfamily of Leguminosae) and is also present in Rubiaceae, Passifloraceae and Polypodiaceae (Donnelly and Sheridan 1988). They are based on 4-phenylcoumarin skeleton. Neoflavonoid include 4-arylcoumarins (neoflavones), 4-arylchromanes, dalbergiones and dalbergiquinols (Garazd et al., 2003). Depending on the position of phenyl ring three major classes of flavonoids can be identified: flavonoids (phenyl ring at the C-2 position), isoflavonoids (phenyl ring at the C-3 position) and neoflavonoids (phenyl ring at the C-4 position) (Sarbu et al., 2019). Beside these three major classes a fourth category is identified as minor flavonoid which consists of chalcones and aurones that do not have benzopyran backbone (Sarbu et al., 2019). Derivatives of neoflavonoid also named as 4-arylcoumarins possess biological activity like antimicrobial, antioxidant, cytotoxic etc. (Wang et al., 2017).
Neoflavones display antibacterial activity. Structural activity exhibited function related to antimicrobial activity. Lactone opened ring in neoflavonoids showed effective inhibition (Son et al., 2018). Garazd et al.(2003) present physico-chemical data of neoflavones, mesuagin and mesuarin neoflavones exhibit antibacterial activity. Neoflavonoid S(+)-3’-hydroxy-4’,2,4,5-tetramethoxydalbergiquinol and a benzofuran together with two known neoflavonoids from Dalbergia melanoxylon were tested for their inhibitory activity against microorganisms. All compounds showed weak activity or were inactive (Lin et al., 2020). The open-chain neoflavonoids can be subdivided according to their oxidation level giving dalbergiquinol, dalbergione and benzophenone groups (Donnelly and Sheridan 1988). It is interesting to compare the compounds of different oxidation levels isolated from one Dalbergia species.
According to the molecular structure the neoflavonoids can be divided into dalbergiphenols, dalbergiones, dalbergins, benzophenones and other types (Liu et al., 2017). The three neoflavonoids as listed:
- (1S,8R,9S)-1,5-dihydroxy-4,12-dimethoxy-8-vinyl-tricyclo[7.3.1.02,7]trideca-2,4,6,11-tetraen-10-one
- 2,5,2’,5’-tetrahydroxy-4-methoxy-4-methoxybenzophenone
- 2,5,3’-trihydroxy-4-methoxybenzophenone
are evaluated for inhibitory activity against three fungal and seven bacterial strains. However none of the three neoflavonoids showed potential antimicrobial activities in vitro (Wang et al., 2020). Neoflavonoid and various other isoflavonoids prevent colonization of plant by plant pathogens. They act as natural defense molecules for plant.
References:
Bozkurt, I. A. and Soylu, S. 2011 Determination of Responses of Different Bean Cultivars against Races of Pseudomonas syringae pv phaseolicola, Causal Agent of Halo Blight of Bean. Euphytica 179: 417 – 425
doi.org/10.1007/s10681-010-0339-0
Donnelly, D. M. X. and Sheridan, H. 1988 Neoflavonoids. In: “The Flavonoid”. Harborne, J. B. (ed.). Chapman and Hall Ltd. London. pp: 211 – 232
doi: 10.1007/978-1-4899-2913-6_6
Garazd, M. M., Garazd, Y. L. and Khilya, V. P. 2003 Neoflavones. 1. Natural Distribution and Spectral and Biological Properties. Chem. Nat. Compd. 39(1): 54 – 121
doi: 10.1023/A:1024140915526
Gnanamanickam, S. S. and Patil, S. S. 1977 Accumulation of Antibacterial Isoflavonoids in Hypersensitively Responding Bean Leaf Tissues Inoculated with Pseudomonas phaseolicola. Physiol. Plant Pathol. 10(2): 159 – 168
doi.org/10.1016/0048-4059(77)90019-4
Hargreaves, J. A. 1980 A Possible Mechanism for the Phytotoxicity of the Phytoalexin Phaseollin. Physiol. Plant Pathol. 16(3): 351 – 357
doi.org/10.1016/S0048-4059(80)80007-5
Lin, S., Liu, R-H., Ma, G-Q., Mei, D-Y., Shao, F. and Chen, L-Y. 2020 Two New Compounds from the Heartwood of Dalbergia melanoxylon. Nat. Prod. Res. 34(19): 2794- 2801
doi: 10.1080/14786419.2019.1591397
Liu, R-H., Lin, S., Zhang, P-Z., Chen, L-Y., Huang, H-L. and Mei, D-Y. 2017 Neoflavonoids and their Pharmacological Activities in Dalbergia genus. Zhongguo Zhong Yao Za Zhi. 42(24): 4707 – 4715
doi: 10.19540/j.cnki.cjcmm.20170928.013
Sarbu, L. G., Bahrin, L. G., Babil, C., Stefan, M. and Birsa, M. L. 2019 Synthetic Flavonoids with Antimicrobial Activity: A Review. J. Appl. Microbiol. 127(5): 1282 – 1290
doi.org/10.1111/jam.14271
Smith, D. A. 1976 Some Effect of the Phytoalexin, Kievitone on the Vegetative Growth of Aphanomyces euteiches, Rhizoctonia solani and Fusarium solani f. sp. phaseoli. Physiol. Plant Pathol. 9(1): 45 – 48
doi.org/10.1016/0048-4059(76)90074-6
Smith, D. A., VanEtten, H. D. and Bateman, D. F. 1975 Accumulation of Phytoalexins in Phaseolus vulgaris hypocotyls Following Infection by Rhizoctonia solani. Physiol. Plant Pathol. 5(1): 51 – 64
doi.org/10.1016/0048-4059(75)90070-3
Smith, D. A., Van Etten, H. D. and Bateman, D. F. 1973 Kievitone: the Principal Antifungal Component of “Substance II” Isolated from Rhizoctonia Infected Bean Tissues. Physiol. Plant Pathol. 3(2): 179 – 184
doi.org/10.1016/0048-4059(73)90080-5
Son, N. T., Oda, M., Hayashi, N., Yamaguchi, D., Kawagishi, Y., Takahashi, F., Harada, K., Cuong, N. M. and Fukuyama, Y. 2018 Antimicrobial Activity of the Constituents of Dalbergia tonkinensis and Structural-Bioactive Highlights. Nat. Prod. Communication 13(2):
doi.org/10.1177/1934578X1801300212
Soriano-Richards, E., Uribe-Salas, D. and Ibarra-Barrera, G. 1998 Phaseollidin Stored in Vacoules and the Phytoalexin Response in Bean. Plant Pathol. 47(4): 480 – 485
doi.org/10.1046/j.1365-3059.1998.00264.x
Theodorou, M. K. and Smith, I. M. 1979 The Response of French Bean Varieties to Components Isolated from Races of Colletotrichum lindemuthianum. Physiol. Plant Pathol. 15(3): 297 – 309
doi.org/10.1016/0048-4059(79)90081.x
Turbek, C. S., Smith, D. A. and Schardl, C. L. 1992 An Extracellular Enzyme from Fusarium solani f. sp. phaseoli which Catalyses Hydration of the Isoflavonoid Phytoalexin Phaseollidin. FEMS Microbiol. Lett. 94(1-2): 187 -190
doi.org/10.1111/j.1574-6968.1992.tb05312.x
Wang, M-F., Ma, G-Q., Shao, F., Liu, R-H., Chen, L-Y., Liu, Y., Yang, L. and Meng, X-W. 2020 Neoflavonoids from the Heartwood of Dalbergia melanoxylon. Nat. Prod. Res. 1-7
doi: 10.1080/14786419.2020.1800692
Wang, B., Li, N., Liu, T., Sun, J. and Wang, X. 2017 Synthesis and Biological Evaluation of Novel Neoflavonoid Derivatives as Potential Antidiabetic Agents. RSC Adv. 7: 34448 – 34460
doi: 10.1039/c7ra06457h
Wyman, J. G. and Van Etten, H. D. 1978 Antibacterial Activity of Selected Isoflavonoids. Phytopathology 68: 583 – 589
BIOLOGICAL PROCESSES- A NATURE'S GIFT 