Sulfur (S) is an essential nutrient required for plant growth and development and has a role in plant resistance against diseases. In plants sulfur and sulfur-containing compounds, directly or indirectly take part in biotic and abiotic stress management, metabolism and signaling (Narayan et al., 2022). Sulfur is a structural component of protein disulfide bonds, amino acids, vitamins and cofactor (Narayan et al., 2022). Most of the sulfur in soil is present in organic matter. While the inorganic sulfate is in inorganic sulfur form (Schoenau and Malhi 2008). The sulfur that is present in soil solution is the sulfate which is available to the plant. The microbial conversion of organic sulfur in the form of humus and crop residues to sulfate is termed as mineralization (Schoenau and Malhi 2008). Microorganisms mobilize organic sulfur in soil through sulfatase activity. Sulfatases are hydrolytic enzymes and sulfatase-producing bacteria are abundant in rhizosphere, and their activity contributes directly to the plant growth-promoting effects (Elkatmis et al., 2026). Pseudomonas putida a rhizosphere bacterium mobilizes bounded sulfur for it to be used by plants as plant nutrition (Kertesz and Mirleau 2004). Application of S in soil in form of inorganic sulfate salts can markedly increase the disease resistance of crop against certain fungal pathogens (Kunstler et al., 2020).
It is worth noting sulfur dioxide can induce stomatal closure like hydrogen sulfide (H2S) but in a less efficient way (Liu et al., 2021). Sulfur and diverse sulfur containing compound contribute to plant defense against a wide array of plant pathogens. H2S a gaseous signaling molecule plays multiple roles in regulation of plant growth, development and plant responses to stress conditions (Vojtovic et al., 2020). Volatile S compound is thought to have a role because H2S is toxic to fungi (Bloem et al., 2004). The release of S-containing gases appears to be part of response to fungal infection (Bloem et al., 2012). Sulfate supply was found to be neutral or beneficial for tolerance against fungal pathogen but neutral for bacterial pathogens under in vitro conditions (Kruse et al., 2007). The study suggest that plant-pathogen interactions and sulfur metabolism are linked by jasmonic acid as signal (Kruse et al., 2007).
Sulfur-containing defense compounds in plant defense response to pathogen includes sulfur containing amino acids such as cysteine and methionine, the tripeptide glutathione, thionins and defensins, glucosinolates and phytoalexins as well as reactive sulfur species and hydrogen sulfide. (Kunstler et al., 2020). Glutathione modulates defense signaling network by cross-communication with plant hormone during biotic stress (Kunstler et al., 2020, Zhu et al., 2021). Glutathione is required for both local and systemic resistance of Nicotiana benthamiana to tobacco mosaic virus infection through a differential modulation of salicylic acid signaling and reactive oxygen species (Zhu et al., 2021). Plants deploy sulfur-rich metabolites, including volatile organic compounds, glucosinolates and the phytoalexin camalexin, to restrict pathogens, modulate beneficial associations and structure rhizosphere communities (Elkatmis et al., 2026). Organosulfur compounds in Allium species such as garlic and onion, act as S-containing phytoanticipins, like glucosinolate (Elkatmis et al., 2026). The sulfur-containing secondary metabolites glucosinolate occur naturally in Brassica species (Rhee et al., 2020). Brassica rotation crop may reduce soilborne potato disease (Larkin and Lynch 2018). Crops in Brassicaceae family such as broccoli, cabbage, cauliflower, kale, turnip, radish, canola, rapeseed and various mustard produce sulfur compound glucosinolates that breaks down to produce isothiocyanates that are toxic to many soil organisms as part of process known as biofumigation (Larkin and Lynch 2018). Biofumigation is beneficial use of Brassica as green manure as they can release isothiocyanates in soil that suppress pest and disease organism (Sarwar et al., 1998; Matthiessen and Kirkegaard 2007). Glucosinolates upon hydrolysis by endogenous thioglucosidases known as myrosinases produce many different products (e.g. isothiocyanates, thiocyanates and nitriles) and these hydrolysis products have several biological activities such as defense compound and attractants (Halkier and Gershenzon 2006).
Cysteine inhibits in a concentration-dependent manner both mycelial growth and the spore germination of the fungal pathogens Phaeomoniella chlamydospora and Phaeoacremonium minimum causing grapevine trunk (esca) disease (Roblin et al., 2018). Cysteine can control fungal diseases either by acting as an early signal directing plant host reaction or/and by acting directly on fungal development (Roblin et al., 2018).
Phytoanticipins and phytoalexins have a role in plant defense against plant pathogens e.g. allicin and camalexins. Allicin is a phytoanticipins i.e. produced from a preformed substrate without further expenditure of cellular energy or metabolism (i.e. passively) upon pathogen attack (Borlinghaus et al., 2014). Garlic plants have alliin/alliinase system, which is responsible for production of allicin in freshly injured tissue, and which has an antimicrobial effect against the pathogens. Allicin being a thiosulfinate is a reactive sulfur species and undergoes redox-reaction with thiol groups in glutathione and proteins, which is thought to be essential for its biological activity (Borlinghaus et al., 2014). Camalexin a phytoalexin of Arabidopsis thaliana is induced in response to various plant pathogens challenge (Glawisching 2007).
Thionins are a small cationic plant peptides with antimicrobial activity. They play a role in plant defense by destroying the cell membranes of pathogens and trigger immune responses (Riseh et al., 2025).
References:
Bloem, E., Riemenschneider, A., Volker, J., Papenbrock, J., Schmidt, A., Salac, I., Haneklaus, S. and Schnug, E. 2004 Sulphur Supply and Infection with Pyrenopeziza brassicae Influence L-cysteine Desulphydrase Activity in Brassica napus L. J. Exp. Bot. 55(406): 2305 – 2312
doi: 10.1093/jxb/erh236
Bloem, E., Haneklaus, S., Kesselmeier, J. and Schnug, E. 2012 Sulfur Fertilization and Fungal Infection Affect the Exchange of H2S and COS from Agricultural Crops. J. Agric. Food Chem. 60(31): 7588 – 7596
doi.org/10.1021/jf301912h
Borlinghaus, J., Albrecht, F., Gruhlke, M. C. H., Nwachukwu, I. D. and Slusarenko, A. J. 2014 Allicin: Chemistry and Biological Properties. Molecules 19(8): 12591 – 12618
doi: 10.3390/molecules190812591
Elkatmis, B., Turksoy, G. M., Rodriguez, E., Rahmoune, B., Koprivova, A. and Kopriva, S. 2026 Sulfur as a Central Integrator of Plant-Microbe Interactions: From Nutrient Cycling to Immune Signaling and Microbiome Assembly. J. Exp. Bot. pp 01 – 18
doi.org/10.1093/jxb/erag186
Glawischnig, E. 2007 Camalexin. Phytochemistry 68(4): 401 – 406
doi: 10.1016/j.phytochem.2006.12.005
Halkier, B. A. and Gershenzon, J. 2006 Biology and Biochemistry of Glucosinolates. Annu. Rev. Plant Biol. 57: 303 – 333
doi.org/10.1146/annurev.arplant.57.032905.105228
Kertesz, M. and Mirleau, P. 2004 The Role of Soil Microbes in Plant Sulphur Nutrition. J. Exp. Bot. 55(404): 1939 – 1945
dio.org/10.1093/jxb/erh176
Kruse, C., Jost, R., Lipschis, M., Kopp, B., Hartmann, M. and Hell, R. 2007 Sulfur-enhanced Defence: Effects of Sulfur Metabolism, Nitrogen Supply and Pathogen Lifestyle. Plant Biol. (Stuttg) 9(5): 608 – 619
doi: 10.1055/s-2007-965432
Kunstler, A., Gullner, G., Adam, A. L., Nagy, J. K. and Kiraly, L. 2020 The Versatile Roles of Sulfur-Containing Biomolecules in Plant Defense-A Road to Disease Resistance. Plant (Basel) 9(12): 1705
doi: 10.3390/plants9121705
Larkin, R. P. and Lynch, R. P. 2018 Use and Effects of Different Brassicas and Other Rotation Crops on Soilborne Diseases and Yield of Potato. Horticulturae 4(4): 37
doi.org/10.3390/horticulturae4040037
Liu, H., Wang, J., Liu, J., Liu, T. and Xue, S. 2021 Hydrogen Sulfide (H2S) Signaling in Plant Development and Stress Responses. aBIOTECH 2(1): 32 – 63
doi: 10.1007/s42994-021-00035-4
Matthiessen, J. and Kirkegaard, J. A. 2007 Biofumigation and Enhanced Biodegradation: Opportunity and Challenge in Soilborne Pest and Disease Management. Critical Reviews in Plant Sciences 25(3): 235 – 265
doi: 10.1080/07352680600611543
Narayan, O. P., Kumar, P., Yadav, B., Dua, M. and Johri, A. K. 2022 Sulfur Nutrition and its Role in Plant Growth and Development. Plant Signal. Behav. 18(1): 2030082
doi: 10.1080/15592324.2022.2030082
Rhee, J-H., Choi, S., Lee, J-E., Hur, O-S., Ro, N-Y., Hwang, A-J., Ko, H-C., Chung, Y-J., Noh, J. J. and Assefa, A. D. 2020 Glucosinolate Content in Brassica Genetic Resources and their Distribution Pattern Within and Between Inner, Middle and Outer Leaves. Plant (Basel) 9(11): 1421
doi: 10.3390/plants9111421
Riseh, R. S., Fathi, F., Vatankhah, M. and Kennedy, J. F. 2025 Thionins: Potential Use in Plant Defense against Pathogens. Plant Mol. Biol. 115(4): 77
doi: 10.1007/s11103-025-01612-7
Roblin, G., Octave, S., Faucher, M., Fleurat-Lessard, P. and Berjeaud, J-M. 2018 Cysteine: A Multifaceted Amino Acid Involved in Signaling Plant Resistance and Antifungal Development. Plant Physiol. Biochem. 129: 77 – 89
doi: 10.1016/j.plaphy.2018.05.024
Sarwar, M., Kirkegaard, J. A., Wong, P. T. W. and Desmarchelier, J. M. 1998 Biofumigation Potential of Brassicas. Plant and Soil 201(1): 103 – 112
doi: 10.1023/A:1004381129991
Schoenau, J. J. and Malhi, S. S. 2008 Sulfur Forms and Cycling Processes in Soil and their Relationship to Sulfur Fertility. In: “Sulfur: A Missing Link Between Soils, Crops and Nutrition”. Jez, J. (eds.). Volume 50 Book Series: Agronomy Monographs Chapter 1: Pages 01 – 10
doi.org/10.2134/agronmonogr50.c1
Vojtovic, D., Luhova, L. and Petrivalsky, M. 2020 Something Smells Bad to Plant Pathogens: Production of Hydrogen Sulfide in Plants and its Role in Plant Defense Responses. J. Adv. Res. 27: 199 – 209
doi: 10.1016/j.jare.2020.09.005
Zhu, F., Zhang, Q-P., Che, Y-P., Zhu, P-X., Zhang, Q-Q. and Ji, Z-L. 2021 Glutathione Contributes to Resistance Responses to TMV through a Differential Modulation of Salicylic Acid and Reactive Oxygen Species. Mol. Plant Pathol. 22(12): 1668 – 1687
doi: 10.1111/mpp.13138
BIOLOGICAL PROCESSES- A NATURE'S GIFT 