Biochemical and physiological changes in maize plants supplied with silicon and infected by Exserohilum turcicum

Northern leaf blight (NLB), caused by Exserohilum turcicum, is one of the most important diseases affecting maize production worldwide. The effect of silicon (Si) on maize resistance against NLB was investigated through an in-depth analysis of physiological and biochemical changes (measurements of gas exchange and chlorophyll (Chl) a fluorescence parameters, activities of host defence enzymes and those involved in the antioxidative metabolism, and the determination of other metabolites) on plants non-supplied (-Si) or supplied (+Si) with Si and inoculated with E. turcicum. Higher foliar Si concentration contributed to reducing the foliar NLB symptoms in +Si plants. Both antioxidant (ascorbate peroxidase, catalase, glutathione reductase and peroxidase) and host defence (chitinase, beta-1,3-glucanase, polyphenoloxidase and phenylalanine ammonia-lyase) enzymes had their activities greater for +Si plants compared to -Si plants. Lower levels of hydrogen peroxide and malondialdehyde were obtained for +Si plants in contrast to -Si plants. Net CO2 assimilation rate, stomatal conductance to water vapour, transpiration rate and internal CO2 concentration had their values significantly increased for +Si plants compared to -Si plants from 5 to 20 days after inoculation. The maximum quantum yield of photosystem II, effective quantum yield of the photosystem, quantum yield of regulated energy dissipation and quantum yield of non-regulated energy dissipation were less impacted on the leaves of +Si plants compared to -Si plants. The Chl a concentration was kept higher for +Si plants than for -Si plants. Taken together, this study brings biochemical and physiological pieces of evidence that a more robust antioxidative metabolism, great activities of host defence-related enzymes and the preservation of the photosynthetic machinery were all potentiated by Si contributing, therefore, for less NLB symptoms.

Automated summary

Silicon can effectively enhance maize resistance against Northern leaf blight (NLB) by reducing foliar symptoms, increasing activities of antioxidant and host defense enzymes, and maintaining photosynthetic efficiency.