Abstract
Main conclusion
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.
Abstract
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.
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Abbreviations
- AAS:
-
Atomic absorption spectrophotometry
- DAI:
-
Days after inoculation
- EDX:
-
Energy-dispersive X-ray spectroscopy
- ESEM:
-
Environmental scanning electron microscopy
- PAL:
-
Phenylalanine ammonia lyase
- POX:
-
Peroxidase
- PPO:
-
Polyphenol oxidase
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Acknowledgements
The authors would like to express their gratitude to Kováč family members for sorghum seed production and harvest, and Zuzana Šulavíková for her technical assistance. We would also like to thank prof. RNDr. Alexander Lux, CSc. for his valuable thoughts and support throughout this project. Furthermore, we greatly appreciate the insightful comments and kind revision of this manuscript by both reviewers and editor. This work was supported by the Scientific Grant Agency of Slovak Republic VEGA [1/0745/20] and by the Grant Agency of Czech Republic [GA 19-03909S] and was also the result of the project implementation: Comenius University in Bratislava Science Park supported by the Research and Development Operational Programme funded by the ERDF [Grant no. ITMS 26240220086].
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Authors MB, RŠ, BB and MM have received research grant from Scientific Grant Agency of Slovak Republic; BB has participated on research grant from Comenius University in Bratislava Science Park supported by the Research and Development Operational Programme funded by the ERDF; and VN and ET have received research grant from Grant Agency of Czech Republic.
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Table S1
Relative enzyme activities of POX, PPO and PAL of all treatments at each DAI. The activities are expressed in relative values, with treatment -Si at 0 DAI considered as 1. Values represent means ± SD. Different letters indicate significant difference among all treatments at P ≤ 0.05 (n = 15, ANOVA, LSD test), with independent statistic evaluation for each DAI. Stat. sign. statistical significance (XLSX 12 KB)
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Bathoova, M., Švubová, R., Bokor, B. et al. Silicon triggers sorghum root enzyme activities and inhibits the root cell colonization by Alternaria alternata. Planta 253, 29 (2021). https://doi.org/10.1007/s00425-020-03560-6
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DOI: https://doi.org/10.1007/s00425-020-03560-6