Flavonoid with two aromatic rings joined by three carbon chain (heterocyclic pyran ring) (C6-C3-C6) are structurally diverse secondary metabolites in plant with different functions. The structural diversity of flavonoids is derived by complex substitution of these carbon skeletons through hydroxylation, glycosylation, methylation, phenylation etc. (Naoumkina et al., 2010). Different modifications of flavonoid skeleton affect their antimicrobial activity. The flavonoid glycoside analogues exhibited antifungal activity against different Fusarium oxysporum f. sp. dianthi   pathotype (Galeotti et al., 2008). The prenylated flavonoids showed antibacterial and antifungal activity (Sohn et al., 2004). Flavonoid with variable phenolic structures are found in fruits, vegetables and certain beverages. They function as signal molecule, phytoalexins, detoxifying agents and antimicrobial defensive compounds (Panche et al., 2016). Flavonoid class include chalcones, aurones, isoflavones, flavones, flavonols, anthocyanins, proanthocyanidins, flavanones and flavanols (Nix et al., 2017). Specialized cells of plant synthesize phenolics and store them in their vacuoles. Such phenolic-storing cells are distributed within most tissues. Beckman (2000) proposed that these cells by decompartmentation, rapid oxidation of their phenolic content followed by lignification and suberization of cells and cell death, seal off infection or injuries at the site of cellular penetration. If this defense fails and the infection persist, then the same processes promote build-up of indole acetic acid (IAA) and ethylene that causes metabolic cascade in cells that includes secondary metabolism and growth response to produce a peridermal defense.  Flavonoid compounds are transported to the site of infection and induce the hypersensitivity reaction, a defense mechanism of plant in response to the infection resulting in programmed cell death (Mierziak et al., 2014).  

Flavonoid inhibit fungal growth either by disrupting plasma membrane or by induction of mitochondrial dysfunction. The inhibition mechanisms may also include cell wall formation, cell division, ribonucleic acid (RNA) and protein synthesis (Al Aboody and Mickymaray 2020).  Increased resistance in older seedlings of cotton to Rhizoctonia solani infection was due to increase in catechin (Hunter 1974), catechin is flavan-3-ol monomer is an effective antifungal defense against rust infection (Ullah et al., 2017). Flavonoid can kill or inhibit bacterial cell by causing membrane disruption, inhibition of nucleic acid synthesis, quorum sensing which impairs their ability to form biofilms, the antimicrobial action can also inhibit cell envelop synthesis  (Gorniak et al., 2019). Sophoraflavanone G isolated from Sophora exigua exerts antibacterial effect by reducing the fluidity of cellular membrane (Tsuchiya and Iinuma 2000).  Many flavonoid have evolved as bioactive compounds that interfere with nucleic acid or proteins and show antimicrobial or insecticidal properties (Panche et al., 2016). Flavonoid can modulate the activity of auxin-transporting P-glycoproteins and appears to modulate the activity of regulatory proteins such as phosphatases and kinases (Peer and Murphy 2007).  Rutin a flavonoid can function as an activator to improve plant disease resistance (Yang et al., 2016). Polyphenol-rich plant extract may have antibacterial activity (Taguri et al., 2006). Rutin classified as a polyphenolic substance exhibits bactericidal and fungicidal activity in vitro assay. Polyphenolic substances disrupt the cell wall and the cell membrane integrity of microbial cells thereby releases intracellular components (Yang et al., 2016), inhibits nucleotide synthesis and ATP synthesis resulting in inhibition of microorganism (Ahmad et al., 2012). Kaempferol a polyphenol can bind to DNA helicase and inhibits its ATPase activity (Adamczak et al., 2020). Likic et al. (2014) propose modulation of IAA transport through the action of kaempferol has a regulatory role in plant defense responses against virus infection. They also suggest kaempferol to be part of auxin dependent defense response which limits virus infection and that this defense response is activated prior to salicylic acid dependent defense response.

Flavonoid and nitrogenous metabolites such as alkaloids, terpenoids, peptides and amino acids are components of plant seeds. Conjugated form of these compounds are soluble in water and are released in soil. These metabolites in soil may serve as eco-sensing signals for rhizobia and arbuscular mycorrhiza for establishment of symbioses. They may also serve as defense molecules against pathogens and insect pests and can control the plant pest (Striga) of cereal crops (Ndakidemi and Dakora 2003).

Formation of reactive oxygen species (ROS), a by-product of oxidation/reduction (redox) reaction can attack biomolecule causing DNA mutation, protein denaturation and membrane lipid peroxidation they disturb normal cellular metabolism and cause molecular damage or if severe can result in cell death (Racchi 2013). Flavonoid play a role as antioxidant agent and scavenge ROS which are generated on pathogen attack. Flavonoid reduce the production of ROS either by suppression of singlet oxygen or by inhibition of ROS-generating enzymes (cyclooxygenase, lipoxygenase, monooxygenase and xanthine oxidase) or by chelation of transition metal ions which may catalyse ROS production (Mierziak et al., 2014). Flavonoid comprises of phenolic compound with range of biological function. Many biological roles of flavonoid is attributed to cytotoxicity and antioxidant abilities (Pourcel et al., 2007). The variability in content and composition of phenolic compounds provides opportunity to develop resistant cultivar to pathogen attack.  

                                             See Part V (B) for further information ……..


Adamczak, A., Ozarowski, M. and Karpinski, T. M. 2020 Antibacterial Activity of Some Flavonoids and Organic Acids Widely Distributed in Plants. J. Clin. Med. 9(1): 109


Ahmad, Z., Ahmad, M., Okafor, F., Jones, J., Abunameh, A. M., Cheniya, R. K. and Kady, I. O. 2012 Effect of Structural Modulation of Polyphenolic Compounds on the Inhibition of Escherichia coli ATP synthase. Int. J. Biol. Macromol. 50(3): 476 – 486

doi: 10.1016/j.ijbiomac.2012.01.019

Al Aboody, M. S. and Mickymaray, S. 2020 Anti-Fungal Efficacy and Mechanisms of Flavonoids. Antibiotics 9(2): 45

doi: 10.3390/antibiotics9020045

Beckman, C. H. 2000 Phenolic-Storing Cells: Keys to Programmed Cell Death and Periderm Formation in Wilt Disease Resistance and in General Defence Responses in Plants? PMPP 57(3): 101 – 110

Galeotti, F., Barile, E., Curir, P., Dolci, M. and Lanzotti, V. 2008 Flavonoids from Carnation (Dianthus caryophyllus) and their Antifungal Activity. Phytochem. Lett. 1(1): 44 – 48

Gorniak, I., Bartoszewski, R. and Kroliczewski, J.    2019 Comprehensive Review of Antimicrobial Activities of Flavonoids. Phytochem. Rev. 18: 241 – 272                          

Hunter, R. E. 1974 Inactivation of Pectic Enzymes by Polyphenols in Cotton Seedlings of Different Ages Infected with Rhizoctonia solani. Physiol. Plant Pathol. 4(2): 151 – 159

Likic, S., Sola, I., Ludwig-Muller, J. and Rusak, G. 2014 Involvement of Kaempferol in the Defense Response of Virus Infected Arabidopsis thaliana. Eur. J. Plant Pathol. 138(2): 257 – 271

doi: 10.1007/s10658-013-0326-0

Mierziak, J., Kostyn, K. and Kulma, A. 2014 Flavonoids as Important Molecules of Plant Interactions with the Environment. Molecules 19(10): 16240 – 16265

doi: 10.3390/molecules191016240

Naoumkina, M. A., Zhao, Q., Gallego-Giraldo, L., Dai, X., Zhao, P. X. and Dixon, R. A. 2010 Genome-wide Analysis of Phenylpropanoid Defense Pathways. Mol. Plant Pathol. 11(6): 829 – 846

doi: 10.1111/j.1364-3703.2010.00648.x

Ndakidemi, P. A. and Dakora, F. D. 2003 Legume Seed Flavonoids and Nitrogenous Metabolites as Signals and Protectants in Early Seedling Development. Functional Plant Biol. 30(7): 729 – 745

doi: 10.1071/fp03042

Nix, A., Paull, C. and Colgrave, M. 2017 Flavonoid Profile of the Cotton Plant Gossypium hirsutum. Plants 6 (43): 1 – 14

doi: 10.3390/plants6040043

Panche, A. N., Diwan, A. D. and Chandra, S. R. 2016 Flavonoids: An Overview. J. Nutr. Sci. 5: e47

doi: 10.1017/jns.2016.41

Peer, W. A. and Murphy, A. S. 2007 Flavonoids and Auxin Transport: Modulators or Regulators? Trends Plant Sci. 12(12): 556 – 563

doi: 10.1016/j.tplants.2007.10.003

Pourcel, L., Routaboul, J-M., Cheynier, V., Lepiniec, L. and Debeaujon, I. 2007 Flavonoid Oxidation in Plants: from Biochemical Properties to Physiological Functions. Trends Plant Sci. 12(1): 29 – 36

doi: 10.1016/j.tplants.2006.11.006

Racchi, M. L. 2013 Antioxidant Defenses in Plants with Attention to Prunus and Citrus spp. Antioxidants (Basel) 2(4): 340 – 369

doi: 10.3390/antiox2040340

Sohn, H. Y., Son, K. H., Kwon, C. S., Kwon, G. S. and Kang, S. S. 2004 Antimicrobial and Cytotoxic Activity of 18 Prenylated Flavonoids Isolated from Medicinal Plants: Morus alba L., Morus mongolica Schneider, Broussnetia papyrifera(L.) Vent, Sophora flavescens Ait and Echinosophora koreensis Nakai. Phytomedicine 11(7 – 8): 666 – 672

doi: 10.1016/j.phymed.2003.09.005

Taguri, T., Tanaka, T. and Kouno, I. 2006 Antibacterial Spectrum of Plant Polyphenols and Extract Depending upon Hydroxyphenyl Structure. Biol. Pharm. Bull. 29(11): 2226 – 22235

doi: 10.1248/bpb.29.2226

Tsuchiya, H. and Iinuma, M. 2000 Reduction of Membrane Fluidity by Antibacterial Sophoraflavanone G Isolated from Sophora exigua. Phytomedicine 7(2): 161 – 165

Ullah, C., Unsicker, S. B., Fellenberg, C., Constabel, C. P., Schmidt, A., Gershenzon, J. and Hammerbacher, A. 2017 Flavan-3-ols are an Effective Chemical Defense against Rust Infection . Plant Physiol. 175(4): 1560 – 1578

doi: 10.1104/pp.17.00842

Yang, W., Xu, X., Li, Y., Wang, Y., Li, M., Wang, Y., Ding, X. and Chu, Z. 2016 Rutin-Mediated Priming of Plant Resistance to Three Bacterial Pathogens Initiating the Early SA Signal Pathway. PLoS One 11(1):e0146910

doi: 10.1371/journal.pone.0146910

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