Phenolic compounds enter soil via plant root secreting root exudates or as leachates or as plant residue decomposition. Generally phenolic compounds released from seeds, roots or residue decomposition can act against soil borne pathogens and root feeding insect (Ndakidemi and Dakora 2003; Mandal et al., 2010). Phenolics usually accumulate in the central vacuoles of the guard cells and epidermal cells as well as in subepidermal cells of leaves and shoot (Lattanzio et al., 2006). Few phenolics are covalently linked to the plant cell wall, while others occur in waxes or on the external surfaces of the plant organ. Past studies also suggest deposition of flavonoids in nuclei of certain tree species, suggesting that flavonoid-DNA complex provides mutual protection against oxidative damage (Sharma and Sharma 1999; Lattanzio et al., 2006). Phenolic storing cells are distributed within most tissues. It is proposed that these cells by decompartmentation, rapid oxidation of their phenolic content, further lead to lignification and suberization of cells, cell death, seal off infection or injuries at the infection site as a defense response against the pathogen attack (Beckman 2000).
Plant phenolics may be divided into two forms i) Constitutive phenolics function as preformed inhibitors associated with nonhost resistance and ii) Induced phenolics that are synthesized in response to the abiotic and biotic stress (Hammerschmidt et al., 2001; Nicholson and Hammerschmidt 1992; Dixon et al., 2002). Phenolics in soil exists in three forms (Min et al., 2015):
- as a dissolved form, which moves freely in soil solution
- a sorbed form which is reversibly bounded to the soil particles or proteins and
- a polymerized form, consisting of humic substances
Plants produce phenolic allelochemicals including simple phenolics, however phenolic allelochemicals from dead plants and crops are lignin-related phenolics acids (Mushtaq and Fauconnier 2024). Cinnamic acid derivatives, notably t-cinnamic, p-coumaric, ferulic and vanillic acids possess antifungal activity (Tawata et al., 1996; Kim et al., 2004; Bisogno et al., 2007). Phenolic allelochemicals can increase cell membrane permeability. Consequently, leakage of cell content and increased lipid peroxidation leading to slow growth or death of plant tissue. In addition, phenolic allelochemicals can inhibit plant from absorbing nutrients from the surroundings and affect the normal growth of the plants (Li et al., 2010). Phenol protocatechuic acid and catechol from onion are toxic substance that provides resistance against the fungus Colletotrichum circinans causing onion smudge disease (Link and Walker 1933). Allelochemical phenolics such as ferulic acid and cinnamic acid can inhibit protein synthesis in Latuca sativa L. (Cameron and Julian 1980). Phenolics exert allelopathic effects on various physiological processes in plants such as inhibition of cell division, elongation and submicroscopic structures, various enzymes functions and activities, synthesis of plant endogenous hormones and protein synthesis (John and Sarda 2012). The production, release and addition of several phenolics act as defense mechanisms against herbivores, pest and pathogens (Misra et al., 2023).
Many of the phenolic root exudate serve as a chemotactic signal for several soil microorganisms that recognize them and move towards the plant roots in a carbon-rich rhizosphere (Taylor and Grotewold 2005). Different organisms are repelled from or attracted towards the same chemical, which then elicit different responses in different organisms. Example, isoflavones from soybean roots serve as an attractant for both the symbiotic Bradyrhizobium japonicum and the pathogenic Phytophthora sojae (Morris et al., 1998). The zoospores of soybean pathogen Phytophthora sojae respond chemotactically to the soybean isoflavones daidzein and genistein exuded from the roots of soybean in the rhizosphere, suggesting the hyphal tips from zoospores that have encysted adjacent to root may use specific host isoflavones to locate their host (Morris et al., 1998).
Beneficial bacteria and fungi as well as bacterial pathogen can induced phenolic production (Wallis and Galarneau 2020). Phenolic production is associated with salicylic acid resistance response, and interaction between jasmonic acid and salicylic acid may have a role in regulating and fine tuning the induced defense which is activated in response to the pathogen attack or insect attack or wounding (Yang et al., 2011; Wallis and Galarneau 2020). Phenolic compounds are often increased following attack during hypersensitive response that leads to cell death. Insects need living tissues for successful feeding would inhibit host defense response (Wallis and Galarneau 2020). Solanaceous plant release endogenous phenolic substances in response to pathogen attack. Whereas the exogenous phenolic substances function to prevent and control pest and diseases during the production of solanaceous plants (Wang et al., 2024). Different type of resistance strategy produce cost, especially cost associated with inducible defenses (Purrington 2000). Plants that suffer frequent and serious damage may invest mainly in constitutive defense, while plants that are attacked rarely may rely on induced defense (Wittstock and Gershenzon 2002; Lattanzio et al., 2006).
References:
Beckman, C. H. 2000 Phenolic-Storing Cells: Keys to Programmed Cell Death and Periderm Formation in Wilt Disease Resistance and in General Defense Responses in Plants? Physiol. Mol. Plant Pathol. 57(3): 101 – 110
doi.org/10.1006/pmpp.2000.0287
Bisogno, F., Mascoti, L., Sanchez, C., Garibotto, F., Giannini, F., Kurina-Sanz, M., Enriz, R. 2007 Structure-antifungal Activity Relationship of Cinnamic Acid Derivatives. J. Agric. Food Chem 55(26): 10635–10640
doi: 10.1021/jf0729098
Cameron, H. J. and Julian, G. R. 1980 Inhibition of Protein Synthesis in Lettuce (Latuca sativa L.) by Allelopathic Compounds. J. Chem. Ecol. 6(6): 989 – 995
doi: 10.1007/bf00994656
Dixon, R. A., Achnine, L., Kota, P., Liu, C-J., Reddy, M. S. S. and Wang, L. 2002 The Phenylpropanoid Pathway and Plant Defence-A Genomics Perspective. Mol. Plant Pathol. 3(5): 371 – 390
doi: 10.1046/j.1364-3703.2002.00131.x
Hammerschmidt, R., Metraux, J. P. and Van Loon, L. C. 2001 Inducing Resistance: A Summary oof Papers Presented at the First International Symposium on Induced Resistance to Plant Diseases, Corfu, May 2000. Eur. J. Plant Pathol. 107: 1-6
doi: 10.1023/A:1008753630626
John, J. and Sarda, S. 2012 Role of Phenolics in Allelopathic Interaction. Allelopathy J. 29(2): 215 -230
Kim, J. H., Campbell, B. C., Mahoney, N. E., Chan, K. L. and Molyneux, R. J. 2004 Identification of Phenolics for Control of Aspergillus flavus Using Saccharomyces cerevisiae in a Model Target-Gene Bioassay. J. Agric. Food Chem. 52(26): 7814–7821
doi: 10.1021/jf0487093
Lattanzio, V., Lattanzio, V. M. T. and Cardinali, A. 2006 Role of Phenolics in the Resistance Mechanisms of Plants against Fungal Pathogens and Insects. In: “Phytochemistry: Advances in Research”. Imperato, F (ed.). Publisher: Research Signpost 37/661 (2), Fort P.O., Trivandrum-695023 Kerala, India. Chapter 2, Page 23 – 67
Li, Z-H., Wang, Q., Ruan, X., Pan, C-D. and Jiang, D-A. 2010 Phenolics and Plant Allelopathy. Molecules 15(12): 8933 – 8952
doi: 10.3390/molecules15128933
Link, K. P. and Walker, J. C. 1933 The Isolation of Catechol from Pigmented Onion Scales and its Significance in Relation to Disease Resistance in Onions. J. Biological Chem. 100(2): 379 – 383
doi.org/10.1016/S0021-9258(18)75955-3
Mandal, S. M., Chakraborty, D. and Dey, S. 2010 Phenolic Acids Act as Signaling Molecules in Plant-Microbe Symbioses. Plant Signal Behav. 5(4): 359 – 368
doi: 10.4161/psb.5.4.10871
Min, K., Freeman, C., Kang, H. and Choi, S-U. 2015 The Regulation by Phenolic Compounds of Soil Organic Matter Dynamics Under Changing Environment. BioMed Res. Internat. 1: 825098
doi.org/10.1155/2015/825098
Misra, D., Dutta, W., Jha, G. and Ray, P. 2023 Interactions and Regulatory Functions of Phenolics in Soil-Plant-Climate Nexus. Agronomy 13(2): 280
doi.org/10.3390/agronomy13020280
Morris, P. F., Bone, E. and Tyler, B. M. 1998 Chemotropic and Contact Responses of Phytophthora sojae Hyphae to Soybean Isoflavonoids and Artificial Substrates. Plant Physiol. 117(4): 1171 – 1178
doi: 10.1104/pp.117.4.1171
Mushtaq, W. and Fauconnier, M-L. 2024 Phenolic Profiling Unravelling Allelopathic Encounters in Agroecology. Plant Stress 13: 100523
doi.org/10.1016/j.stress.2024.100523
Ndakidemi, P. A. and Dakora, F. D. 2003 Legume Seeds Flavonoids and Nitrogenous Metabolites as Signals and Protectants in Early Seedling Development. Funct. Plant Biol. 30(7): 729 – 745
doi: 10.1071/FP03042
Nicholson, R. L. and Hammerschmidt, R. 1992 Phenolic Compounds and their Role in Disease Resistance. Annu. Rev. Phytopathol. 30: 369 – 389
doi.org/10.1146/annurev.py.30.090192.002101
Purrington, C. B. 2000 Costs of Resistance. Curr. Opin. Plant Biol. 3(4): 305 – 308
doi: 10.1016/s1369-5266(00)00085-6
Sharma, A. D. and Sharma R. 1999 Anthocyanin-DNA Copigmentation Complex: Mutual Protection against Oxidative Damage. Phytochemistry 52(7): 1313 – 1318
doi.org/10.1016/S0031-9422(99)00427-6
Tawata, S., Taira, S., Kobamoto, N., Zhu, J., Ishihara, M. and Toyama, S. 1996. Synthesis and Antifungal Activity of Cinnamic Acid Esters. Biosci. Biotechnol and Biochem. 60(5): 909–910
doi: 10.1271/bbb.60.909
Taylor, L. P. and Grotewold, E. 2005 Flavonoids as Developmental Regulators. Curr. Opin. Plant Biol. 8(3): 317 – 323
doi: 10.1016/j.pbi.2005.03.005
Wallis, C. M. and Galarneau, E. R. A. 2020 Phenolic Compound Induction in Plant-Microbe and Plant-Insect Interactions: A Meta-Analysis. Front. Plant Sci. 11: 580753
doi: 10.3389/fpls.2020.580753
Wang, J., Wang, J., Yue, Z., Luo, S., Zhang, B., Yu, J. and Liu, Z. 2024 Disease and Pest Resistance through Phenolic Substances in the Solanaceae. J. Plant Growth Regul. 43: 2121 – 2136
doi:10.1007/s00344-024-11265-3
Wittstock, U. and Gershenzon, J. 2002 Constitutive Plant Toxins and their Role in Defense against Herbivores and Pathogens. Curr. Opin. Plant Biol. 5(4): 300 – 307
doi.org/10.1016/S1369-5266(02)00264-9
Yang, H-R., Tang, K., Liu, H-T. and Huang, W. D. 2011 Effect of Salicylic Acid on Jasmonic Acid-Related Defense Response of Pea Seedlings to Wounding. Scientia Horticulturae 128(3): 166 – 173
doi.org/10.1016/j.scienta.2011.01.015
BIOLOGICAL PROCESSES- A NATURE'S GIFT 