# Aluminum and copper oxide nanoparticles alter secondary metabolites, antioxidants, and biochemical markers in key lime: in vitro approach

## TL;DR

This study examines how aluminum and copper oxide nanoparticles affect key lime plants, revealing toxic effects from copper and potential benefits from aluminum.

## Contribution

The study provides new insights into the differential toxicity of Al2O3 and CuO nanoparticles on lime plants and their biochemical responses.

## Key findings

- CuO-NPs caused toxicity at all concentrations, leading to oxidative stress and lipid peroxidation.
- Al2O3-NPs increased antioxidant compounds and photosynthetic pigments in lime plants.
- Copper accumulation from CuO-NPs disrupted nutrient balance and chelating molecules in lime plants.

## Abstract

The expansive usage of metal oxide nanoparticles (NPs) as a potential constituent in modern nano-enabled products raises threats to environmental safety and crop production. Key lime is an economic plant enriched with secondary metabolites and imperative bioactive compounds. NPs can alter lime’s essential components, making it an ideal model for monitoring NPs’ toxicity. Hence, a comparative analysis of two synthesized metallic NPs, aluminum (Al2O3) and copper (CuO) at concentrations of 0, 100, 200, and 500 mg/L, was conducted to assess their impact on the growth and quality attributes of lime plants under controlled micro-conditions.

Observations from germination, growth, physiological, biochemical, and ionomic attributes showed that Al2O3-NPs had variable effects in a concentration-dependent manner, while CuO-NPs were toxic at all concentrations. Heatmap and principal component analysis revealed that CuO-NPs instigated more pronounced toxic effects compared with Al2O3-NPs at each applied concentration, as evidenced by heightened oxidative stress symptoms. CuO-NPs exerted their toxicity by over-accumulating reactive oxygen radicals and methylglyoxal and elevating lipoxygenase activity, causing peroxidation of membrane lipids and attenuation of photosynthetic pigments. Al2O3-NPs-treated plants relatively up-regulated the pool of phenolics, flavonoids, anthocyanins, ascorbic acid, and α-tocopherol as well as stimulated the activity of enzymatic antioxidants. Ionomics analysis showed excessive copper accumulation in toxic levels (~ 15-fold), which triggered nutritional imbalance (Mg, Si, P, S, Cl, K, Ca, Fe, Cu, and Zn) and disruption of chelating molecules, nitric oxide, and hydrogen sulfide.

This work provides precious insights into the differential impacts of metallic NPs on the development and quality of lime plants and the underlying mechanisms involved in NPs accumulation, highlighting the possible hazards of manufactured NPs in the environment, especially for valuable plant species. However, the controlled use of NPs—particularly aluminum oxide—may offer agronomic benefits, but their application must be carefully handled to prevent toxicity.