Nano calcium alleviates arsenic toxicity in rice (Oryza sativa L.) seedlings via cell wall remodeling and antioxidant defense system

• Nano calcium reduces Cd uptake in roots and enhance nutrition • Nano calcium maintains antioxidant capacity, ion homeostasis to counter As • Nano calcium improves rice growth under As stress • Cell wall play a important role in As detoxification. Arsenic (As) contamination in agricultural soils and water is a serious threat to crop productivity and food safety. Calcium oxide nanoparticles (CaO-NPs), as nanoparticle-based amendments have emerged as a novel technology for heavy-metal toxicity in plants. This study explored the use of CaO-NPs to mitigate As stress in rice seedlings. Rice plants were grown under four treatments: control, As stress, CaO-NP supplementation, and combined CaO-NP+As. We measured growth parameters, chlorophyll content, antioxidant enzyme activities, nutrient uptake, As accumulation, and cell wall properties. Arsenic exposure severely inhibited plant growth and chlorophyll, induced oxidative stress, and elevated As accumulation in tissues. CaO-NP treatment significantly alleviated these effects: seedlings exposed to CaO-NPs+As showed improved morphology, higher chlorophyll content, and enhanced activities of antioxidant enzymes relative to As-alone. CaO-NPs also reduced As accumulation in rice shoots by promoting As sequestration in root cell walls and improving the uptake of essential nutrients like Ca and Fe. CaO-NPs confer tolerance to As by balancing nutrient homeostasis, reducing oxidative damage through a strengthened antioxidant system, and remodeling cell walls to immobilize As. These results highlight the promising capabilities of CaO nanoparticles (CaO-NPs) as a nanotechnological approach for mitigating As toxicity in rice, contributing to safer, more sustainable crop production in contaminated areas.