Silicon inhibits the growth of Alternaria alternata into sorghum root cells by maintaining their integrity through stimulating biochemical defense reactions rather than by silica-based physical barrier creation. Although the ameliorating effect of silicon (Si) on plant resistance against fungal pathogens has been proven, the mechanism of its action needs to be better understood on a cellular level. The present study explores the effect of Si application in sorghum roots infected with fungus Alternaria alternata under controlled in vitro conditions. Detailed anatomical and cytological observations by both fluorescent and electron microscopy revealed that Si supplementation results in the inhibition of fungal hyphae growth into the protoplast of root cells. An approach of environmental scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy enabling spatial detection of Si even at low concentrations showed that there is no continual solid layer of silica in the root cell walls of the rhizodermis, mesodermis and exodermis physically blocking the fungal growth into the protoplasts. Additionally, biochemical evidence suggests that Si speeds up the onset of activities of phenylpropanoid pathway enzymes phenylalanine ammonia lyase, peroxidases and polyphenol oxidases involved in phenolic compounds production and deposition to plant cell walls. In conclusion, Si alleviates the negative impact of A. alternata infection by limiting hyphae penetration through sorghum root cell walls into protoplasts, thus maintaining their structural and functional integrity. This might occur by triggering plant biochemical defense responses rather than by creating compact Si layer deposits.

Comenius University Science Park Comenius University in Bratislava Ilkovicova 8 841 04 Bratislava Slovak Republic

Department of Plant Physiology Faculty of Natural Sciences Comenius University in Bratislava Mlynska dolina Ilkovicova 6 842 15 Bratislava 4 Slovak Republic

Environmental Electron Microscopy Group Institute of Scientific Instruments of the Czech Academy of Sciences Kralovopolska 147 612 00 Brno Czech Republic

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Abbai R, Kim YJ, Mohanan P, Farh MEA, Mathiyalagan R, Yang DU, Rangaraj S, Venkatachalam R, Kim YJ, Yang DC (2019) Silicon confers protective effect against ginseng root rot by regulating sugar efflux into apoplast. Sci Rep 9:18259. https://doi.org/10.1038/s41598-019-54678-x PubMed DOI PMC

Araujo MUP, Rios JA, Silva ET, Rodrigues FA (2019) Silicon alleviates changes in the source-sink relationship of wheat plants infected by Pyricularia oryzae. Phytopathology 109:1129–1140. https://doi.org/10.1094/PHYTO-11-18-0428-R PubMed DOI

Bathoova M, Bokor B, Soukup M, Lux A, Martinka M (2018) Silicon-mediated cell wall modifications of sorghum root exodermis and suppression of invasion by fungus Alternaria alternata. Plant Pathol 67:1891–1900. https://doi.org/10.1111/ppa.12906 DOI

Bekker TF, Kaiser C, van der Merwe R, Labuschagne N (2006) In-vitro inhibition of mycelial growth of several phytopathogenic fungi by soluble potassium silicate. S Afr J Plant Soil 23:169–172. https://doi.org/10.1080/02571862.2006.10634750 DOI

Bennett WF, Tucker BB, Maunder AB (1990) Modern grain sorghum production. Iowa State University Press, Iowa

Bokor B, Vaculík M, Slováková Ľ, Masarovič D, Lux A (2014) Silicon does not always mitigate zinc toxicity in maize. Acta Physiol Plant 36:733–743. https://doi.org/10.1007/s11738-013-1451-2 DOI

Bradford MM (1976) A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal Biochem 72:248–254. https://doi.org/10.1006/abio.1976.9999 DOI

Broggi LE, González HH, Resnik SL, Pacin A (2007) Alternaria alternata prevalence in cereal grains and soybean seeds from Entre Ríos, Argentina. Rev Iberoam Micol 24:47–51. https://doi.org/10.1016/s1130-1406(07)70012-8 PubMed DOI

Bush RK, Prochnau JJ (2004) Alternaria-induced asthma. J Allergy Clin Immunol 113:227–234. https://doi.org/10.1016/j.jaci.2003.11.023 PubMed DOI

Calviño M, Messing J (2012) Sweet sorghum as a model system for bioenergy crops. Curr Opin Biotechnol 23:323–329. https://doi.org/10.1016/j.copbio.2011.12.002 PubMed DOI

Chen D, Cao B, Wang S, Liu P, Deng X, Yin L, Zhang S (2016) Silicon moderated the K deficiency by improving the plant-water status in sorghum. Sci Rep 6:e22882. https://doi.org/10.1038/srep22882 DOI

Coskun D, Deshmukh R, Sonah H, Menzies JG, Reynolds O, Ma JF, Kronzucker HJ, Bélanger RR (2019) The controversies of silicon’s role in plant biology. New Phytol 221:67–85. https://doi.org/10.1111/nph.15343 PubMed DOI

Dallagnol LJ, Rodrigues FA, Pascholati SF, Fortunato AA, Camargo LEA (2015) Comparison of root and foliar applications of potassium silicate in potentiating post-infection defences of melon against powdery mildew. Plant Pathol 64:1085–1093. https://doi.org/10.1111/ppa.12346 DOI

Đorđević B, Neděla V, Tihlaříková E, Trojan V, Havel L (2019) Effects of copper and arsenic stress on the development of Norway spruce somatic embryos and their visualization with the environmental scanning electron microscope. New Biotechnol 48:35–43. https://doi.org/10.1016/j.nbt.2018.05.005 DOI

Elzein A, Heller A, Ndambi B, de Mol M, Kroschel J, Cadisch G (2010) Cytological investigations on colonization of sorghum roots by the mycoherbicide Fusarium oxysporum f. sp. strigae and its implications for Striga control using a seed treatment delivery system. Biol Control 53:249–257. https://doi.org/10.1016/j.biocontrol.2010.02.002 DOI

Epstein E (1994) The anomaly of silicon in plant biology. Proc Natl Acad Sci USA 91:11–17. https://doi.org/10.1073/pnas.91.1.11 PubMed DOI

Exley C (1998) Silicon in life: a bioinorganic solution to bioorganic essentiality. J Inorg Biochem 69:139–144. https://doi.org/10.1016/S0162-0134(97)10010-1 DOI

Exley C (2015) A possible mechanism of biological silicification in plants. Front Plant Sci 6:853. https://doi.org/10.3389/fpls.2015.00853 PubMed DOI PMC

Exley C, Guerriero G, Lopez X (2020) How is silicic acid transported in plants? Silicon 12:2641–2645. https://doi.org/10.1007/s12633-019-00360-w DOI

Fleck AT, Nye T, Repenning C, Stahl F, Zahn M, Schenk MK (2011) Silicon enhances suberization and lignification in roots of rice (Oryza sativa). J Exp Bot 62:2001–2011. https://doi.org/10.1093/jxb/erq392 PubMed DOI

Fortunato AA, da Silva WL, Rodrigues FÁ (2014) Phenylpropanoid pathway is potentiated by silicon in the roots of banana plants during the infection process of Fusarium oxysporum f. sp. cubense. Phytopathology 104:597–603. https://doi.org/10.1094/PHYTO-07-13-0203-R PubMed DOI

Fraser CM, Chapple C (2011) The phenylpropanoid pathway in Arabidopsis. Arabidopsis Book 9:0152. https://doi.org/10.1199/tab.0152 DOI

Frew A, Powell JR, Sallam N, Allsopp PG, Johnson SN (2016) Trade-offs between silicon and phenolic defenses may explain enhanced performance of root herbivores on phenolic-rich plants. J Chem Ecol 42:768–771. https://doi.org/10.1007/s10886-016-0734-7 PubMed DOI

Frič F, Fuchs WH (1970) Veränderungen der Aktivität einiger Enzyme im Weizenblatt in Abhängigkeit von der temperaturlabilen Verträglichkeit für Puccinia graminis tritici. Phytopathology 67:161–174. https://doi.org/10.1111/j.1439-0434.1970.tb02457.x DOI

Guerriero G, Hausman JF, Legay S (2016) Silicon and the plant extracellular matrix. Front Plant Sci 7:463. https://doi.org/10.3389/fpls.2016.00463 PubMed DOI PMC

Guével MH, Menzies JG, Bélanger RR (2007) Effect of root and foliar applications of soluble silicon on powdery mildew control and growth of wheat plants. Eur J Plant Pathol 119:429–436. https://doi.org/10.1007/s10658-007-9181-1 DOI

Hodson MJ, Sangster AG (1993) The interaction between silicon and aluminium in Sorghum bicolor (L.) Moench: growth analysis and X-ray microanalysis. Ann Bot 72:389–400. https://doi.org/10.1006/anbo.1993.1124 DOI

Holbein J, Franke RB, Marhavý P, Fujita S, Górecka M, Sobczak M, Geldner N, Schreiber L, Grundler FMW, Siddique S (2019) Root endodermal barrier system contributes to defence against plant-parasitic cyst and root-knot nematodes. Plant J 100:221–236. https://doi.org/10.1111/tpj.14459 PubMed DOI

Izaguirre-Mayoral ML, Brito M, Baral B, Garrido MJ (2017) Silicon and nitrate differentially modulate the symbiotic performances of healthy and virus-infected Bradyrhizobium-nodulated cowpea (Vigna unguiculata), yardlong bean (V. unguiculata subsp. sesquipedalis) and mung bean (V. radiata). Plants 6:40. https://doi.org/10.3390/plants6030040 DOI PMC

Jiang N, Fan X, Lin W, Wang G, Cai K (2019) Transcriptome analysis reveals new insights into the bacterial wilt resistance mechanism mediated by silicon in tomato. Int J Mol Sci 20:761. https://doi.org/10.3390/ijms20030761 DOI PMC

Johnson SN, Reynolds OL, Gurr GM, Esveld JL, Moore BD, Tory GJ, Gherlenda AN (2019) When resistance is futile, tolerate instead: silicon promotes plant compensatory growth when attacked by above- and belowground herbivores. Biol Lett 15:20190361. https://doi.org/10.1098/rsbl.2019.0361 PubMed DOI PMC

Kar M, Mishra D (1976) Catalase, peroxidase and polyphenoloxidase activities during rice leaf senescence. Plant Physiol 57:315–319. https://doi.org/10.1104/pp.57.2.315 PubMed DOI PMC

Kim SG, Kim KW, Park EW, Choi D (2002) Silicon-induced cell wall fortification of rice leaves: a possible cellular mechanism of enhanced host resistance to blast. Phytopathology 92:1095–1103. https://doi.org/10.1094/PHYTO.2002.92.10.1095 PubMed DOI PMC

Konstantinova P, Bonants PJM, van Gent-Pelzer MPE, van der Zouwen P, van den Bulk R (2002) Development of specific primers for detection and identification of Alternaria spp. in carrot material by PCR and comparison with blotter and plating assays. Mycol Res 106:23–33. https://doi.org/10.1017/S0953756201005160 DOI

Kordalewska M, Brillowska-Dabrowska A, Jagielski T, Dworecka-Kaszak B (2015) PCR and real-time PCR assays to detect fungi of Alternaria alternata species. Acta Biochim Pol 62:707–712. https://doi.org/10.18388/abp.2015_1112 PubMed DOI

Lukačová Z, Švubová R, Kohanová J, Lux A (2013) Silicon mitigates the Cd toxicity in maize in relation to cadmium translocation, cell distribution, antioxidant enzymes stimulation and enhanced endodermal apoplasmic barrier development. Plant Growth Regul 70:89–103. https://doi.org/10.1007/s10725-012-9781-4 DOI

Lukačová Z, Švubová R, Janikovičová S, Volajová Z, Lux A (2019) Tobacco plants (Nicotiana benthamiana) were influenced by silicon and were not infected by dodder (Cuscuta europaea). Plant Physiol Biochem 139:179–190. https://doi.org/10.1016/j.plaphy.2019.03.004 PubMed DOI

Lux A, Luxová M, Hattori T, Inanaga S, Sugimoto Y (2002) Silicification in sorghum (Sorghum bicolor) cultivars with different drought tolerance. Physiol Plant 115:87–92. https://doi.org/10.1034/j.1399-3054.2002.1150110.x PubMed DOI

Lux A, Luxová M, Abe J, Tanimoto E, Hattori T, Inanaga S (2003) The dynamics of silicon deposition in the sorghum root endodermis. New Phytol 158:437–441. https://doi.org/10.1046/j.1469-8137.2003.00764.x DOI

Lux A, Lukačová Z, Vaculík M, Švubová R, Kohanová J, Soukup M, Martinka M, Bokor B (2020) Silicification of root tissues. Plants 9:111. https://doi.org/10.3390/plants9010111 DOI PMC

Ma JF, Tamai K, Yamaji N, Mitani N, Konishi S, Katsuhara M, Ishiguro M, Murata Y, Yano M (2006) A silicon transporter in rice. Nature 440:688–691. https://doi.org/10.1038/nature04590 PubMed DOI

Ma JF, Yamaji N, Mitani N, Tamai K, Konishi S, Fujiwara T, Katsuhara M, Yano M (2007) An efflux transporter of silicon in rice. Nature 448:209–212. https://doi.org/10.1038/nature05964 DOI

Markovich O, Kumar S, Cohen D, Addadi S, Fridman E, Elbaum R (2019) Silicification in leaves of sorghum mutant with low silicon accumulation. Silicon 11:2385–2391. https://doi.org/10.1007/s12633-015-9348-x DOI

Masarovič D, Slováková Ľ, Bokor B, Bujdoš M, Lux A (2012) Effect of silicon application on Sorghum bicolor exposed to toxic concentration of zinc. Biologia 67:706–712. https://doi.org/10.2478/s11756-012-0054-5 DOI

Mattei D, Dias-Arieira CR, Mendes Lopes AP, Miamoto A (2017) Influence of Rocksil DOI

Medeiros HA, Resende RS, Ferreira FC, Freitas LG, Rodrigues FÁ (2015) Induction of resistance in tomato against Meloidogyne javanica by Pochonia chlamydosporia. Nematoda 2:e10015. https://doi.org/10.4322/nematoda.10015 DOI

Mitani N, Chiba Y, Yamaji N, Ma JF (2009) Identification and characterization of maize and barley Lsi2-like silicon efflux transporters reveals a distinct silicon uptake system from that in rice. Plant Cell 21:2133–2142. https://doi.org/10.1105/tpc.109.067884 PubMed DOI PMC

Mohaghegh P, Khoshgoftarmanesh AH, Shirvani M, Sharifnabi B, Nili N (2011) Effect of silicon nutrition on oxidative stress induced by Phytophthora melonis infection in cucumber. Plant Dis 95:455–460. https://doi.org/10.1094/pdis-05-10-0379 PubMed DOI

Murashige T, Skoog F (1962) A revised medium for rapid growth and bio-assays with tobacco tissue cultures. Physiol Plant 15:473–497. https://doi.org/10.1111/j.1399-3054.1962.tb08052.x DOI

Najihah NI, Hanafi MM, Idris AS, Hakim MA (2015) Silicon treatment in oil palms confers resistance to basal stem rot disease caused by Ganoderma boninense. Crop Prot 67:151–159. https://doi.org/10.1016/j.cropro.2014.10.004 DOI

Neděla V, Tihlaříková E, Runštuk J, Hudec J (2018) High-efficiency detector of secondary and backscattered electrons for low-dose imaging in the ESEM. Ultramicroscopy 184:1–11. https://doi.org/10.1016/j.ultramic.2017.08.003 PubMed DOI

Ning D, Song A, Fan F, Li Z, Liang Y (2014) Effects of slag-based silicon fertilizer on rice growth and brown-spot resistance. PLoS ONE 9:102681. https://doi.org/10.1371/journal.pone.0102681 DOI

Ramouthar PV, Caldwell PM, McFarlane SA (2016) Effect of silicon on the severity of brown rust of sugarcane in South Africa. Eur J Plant Pathol 145:53–60. https://doi.org/10.1007/s10658-015-0812-7 DOI

Rasoolizadeh A, Labbé C, Sonah H, Deshmukh RK, Belzile F, Menzies JG, Bélanger RR (2018) Silicon protects soybean plants against Phytophthora sojae by interfering with effector-receptor expression. BMC Plant Biol 18:97. https://doi.org/10.1186/s12870-018-1312-7 PubMed DOI PMC

Ratnayake RMRNK, Daundasekera WAM, Ariyarathne HM, Ganehenege MY (2016) Soil application of potassium silicate reduces the intensity of downy mildew in bitter gourd (Momordica charantia L.) leaves. Ceylon J Sci 45:23–31. https://doi.org/10.4038/cjs.v45i1.7361 DOI

Reissinger A, Winter S, Steckelbroeck S, Hartung W, Sikora RA (2003) Infection of barley roots by Chaetomium globosum: evidence for a protective role of the exodermis. Mycol Res 107:1094–1102. https://doi.org/10.1017/S0953756203008189 PubMed DOI

Rodrigues FÁ, McNally DJ, Datnoff LE, Jones JB, Labbé C, Benhamou N, Menzies JG, Bélanger RR (2004) Silicon enhances the accumulation of diterpenoid phytoalexins in rice: a potential mechanism for blast resistance. Phytopathology 94:177–183. https://doi.org/10.1094/PHYTO.2004.94.2.177 PubMed DOI PMC

Sangster AG, Parry DW (1976) Endodermal silicification in mature, nodal roots of Sorghum bicolor (L.) Moench. Ann Bot 40:373–379. https://doi.org/10.1093/oxfordjournals.aob.a085140 DOI

Sasaki T, Antonio B (2009) Sorghum in sequence. Nature 457:547–548. https://doi.org/10.1038/457547a PubMed DOI

Silva WL, Cruz MFA, Fortunato AA, Rodrigues FA (2015) Histochemical aspects of wheat resistance to leaf blast mediated by silicon. Sci Agric 72:322–327. https://doi.org/10.1590/0103-9016-2014-0221 DOI

Soukup M, Martinka M, Cigáň M, Ravaszová F, Lux A (2014) New method for visualization of silica phytoliths in Sorghum bicolor roots by fluorescence microscopy revealed silicate concentration-dependent phytolith formation. Planta 240:1365–1372. https://doi.org/10.1007/s00425-014-2179-y PubMed DOI

Soukup M, Martinka M, Bosnić D, Čaplovičová M, Elbaum R, Lux A (2017) Formation of silica aggregates in sorghum root endodermis is predetermined by cell wall architecture and development. Ann Bot 120:739–753. https://doi.org/10.1093/aob/mcx060 PubMed DOI PMC

Soukup M, Zancajo VMR, Kneipp J, Elbaum R (2019) Formation of root silica aggregates in sorghum is an active process of the endodermis. J Exp Bot. https://doi.org/10.1093/jxb/erz387 DOI PMC

Spurr AR (1969) A low-viscosity epoxy resin embedding medium for electron microscopy. J Ultrastruct Res 26:31–43. https://doi.org/10.1016/S0022-5320(69)90033-1 PubMed DOI

Thomma BPHJ (2003) Alternaria spp.: from general saprophyte to specific parasite. Mol Plant Pathol 4:225–236. https://doi.org/10.1046/j.1364-3703.2003.00173.x PubMed DOI

Torres MR, Ramos AJ, Soler J, Sanchis V, Marı́n S, (2003) SEM study of water activity and temperature effects on the initial growth of Aspergillus ochraceus, Alternaria alternata and Fusarium verticillioides on maize grain. Int J Food Microbiol 81:185–193. https://doi.org/10.1016/S0168-1605(02)00226-X PubMed DOI

Vaculík M, Landberg T, Greger M, Luxová M, Stoláriková M, Lux A (2012) Silicon modifies root anatomy, and uptake and subcellular distribution of cadmium in young maize plants. Ann Bot 110:433–443. https://doi.org/10.1093/aob/mcs039 PubMed DOI PMC

Van Bockhaven J, Steppe K, Bauweraerts I, Kikuchi S, Asano T, Höfte M, De Vleesschauwer D (2015) Primary metabolism plays a central role in moulding silicon-inducible brown spot resistance in rice. Mol Plant Pathol 16:811–824. https://doi.org/10.1111/mpp.12236 PubMed DOI PMC

Vlašínová H, Neděla V, Đorđević B, Havel L (2017) Bottlenecks in bog pine multiplication by somatic embryogenesis and their visualization with the environmental scanning electron microscope. Protoplasma 254:1487–1497. https://doi.org/10.1007/s00709-016-1036-1 PubMed DOI

Wang T, Chen X, Luo X, Jiang H, Chen M, Wang Z (2018) Formation of Si nanoparticle in Al matrix for Al-7wt.%Si alloy during complex shear flow casting. J Alloys Compd 739:30–34. https://doi.org/10.1016/j.jallcom.2017.12.243 DOI

Weerahewa D, David D (2015) Effect of silicon and potassium on tomato anthracnose and on the postharvest quality of tomato fruit (Lycopersicon esculentum Mill.). J Natl Sci Found Sri Lanka 43:273–280. https://doi.org/10.4038/jnsfsr.v43i3.7959 DOI

Whan JA, Dann EK, Aitken EA (2016) Effects of silicon treatment and inoculation with Fusarium oxysporum f. sp. vasinfectum on cellular defences in root tissues of two cotton cultivars. Ann Bot 118:219–226. https://doi.org/10.1093/aob/mcw095 PubMed DOI PMC

White TJ, Bruns T, Lee SS, Taylor JW (1990) Amplification and direct sequencing of fungal ribosomal RNA genes for phylogenetics. In: Innis MA, Gelfand DH, Sninsky JJ, White TJ (eds) PCR protocols: a guide to methods and applications. Academic Press Inc, New York, pp 315–322

Yamaji N, Sakurai G, Mitani-Ueno N, Ma JF (2015) Orchestration of three transporters and distinct vascular structures in node for intervascular transfer of silicon in rice. Proc Natl Acad Sci USA 112:11401–11406. https://doi.org/10.1073/pnas.1508987112 PubMed DOI

Ye M, Song Y, Long J, Wang R, Baerson SR, Pan Z, Zhu-Salzman K, Xie J, Cai K, Luo S, Zeng R (2013) Priming of jasmonate-mediated antiherbivore defense responses in rice by silicon. Proc Natl Acad Sci USA 110:3631–4363. https://doi.org/10.1073/pnas.1305848110 DOI