Genotype-Dependent Effects of Silicon on Cell Wall Composition and Antioxidant Responses in Oats Under Nitrogen Deficiency

Nitrogen (N) availability strongly regulates plant growth and metabolism, and its deficiency constrains plant development and yield. Silicon (Si) has been reported to enhance plant tolerance to multiple stresses; however, its influence on N metabolism in oats remains poorly understood. This study aimed to investigate the effects of Si on cell wall composition and antioxidant responses in oat genotypes grown under N limitation. Two oat genotypes with contrasting N tolerance were hydroponically cultivated under N-deficient (0.5 mM) or N-sufficient (5 mM) conditions in combination with 0 or 2 mM Si. Growth parameters, N and Si uptake, cell wall structural components, phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase (TAL) activities, antioxidant responses, and oxidative damage were evaluated. In both genotypes grown under N deficiency, Si supply reduced shoot N content while enhancing Si accumulation. Moreover, Si application decreased lipid peroxidation in both genotypes under N-deficient conditions. In the N-sensitive genotype, Si increased cellulose deposition and antioxidant activity, whereas in the N-tolerant genotype, Si reduced lignin content and TAL activity. We conclude that Si supplementation improves the metabolic performance of oat genotypes under N-deficient conditions by modulating nutrient uptake, antioxidant responses, and cell wall composition.