Selenium nanoparticles enhance innate immunity in aphid-stressed oat plants by modulating photosynthetic pigments, sugar, nitrogen and fatty acid metabolism, and antioxidant defense

Oat (Avena sativa L.) is an important cereal crop threatened by insect stress from the grain aphid (Sitobion avenae), which reduces photosynthetic efficiency, sugars, amino acids, and nitrogen metabolism, ultimately impairing plant growth. This study explores the beneficial effects of selenium nanoparticles (SeNPs) on oat plants under grain aphid infestation, focusing on physiological and biochemical responses. Four treatments were applied: non-infested control, SeNP-treated non-infested, aphid-infested control, and SeNPs + aphid-infested plants. Seed priming was performed with a 30 mg L⁻1 SeNP solution, followed by controlled aphid infestation over five weeks, with three replicates per treatment. Aphid stress alone decreased chlorophyll a and b, modified pigment composition, altered sugar profiles, and induced strong shifts in amino acid, fatty acid, and organic acid metabolism. Application of SeNPs to aphid-infested plants significantly enhanced photosynthetic pigments (+ 37% to + 47%), increased soluble sugars (glucose and fructose + 25% to + 34%), and improved total nitrogen content (+ 39%) along with key nitrogen-metabolism enzymes including GDH (+ 113%), GOGAT (+ 46%), and GS (+ 54%). In non-infested plants, SeNPs also increased sucrose accumulation (+ 34%). SeNPs further elevated antioxidant metabolites, with total antioxidant capacity rising by 30% under infestation, and polyphenols and tocopherols increasing by 58% and 33%, respectively. Importantly, SeNP treatment reduced aphid body weight by 30% and decreased apterous morphs by 20%, indicating enhanced plant defensive capacity. In conclusion, the research highlighted the potential of SeNPs to enhance the resilience of oat plants against grain aphid stress by improving physiological parameters, boosting sugar and nitrogen metabolism, and increasing antioxidant levels, resulting in decreased aphid populations and modified growth patterns. Future studies should explore field-scale applications and evaluate long-term ecological and agronomic impacts of nano-enabled insect-stress management strategies.