# Physiological and Metabolic Changes Induced by Fullerene C60 Derivatives in Zinc-Stressed Cucumber

## TL;DR

This study explores how fullerene C60 derivatives can help reduce the harmful effects of excess zinc on cucumber plants, though their effectiveness is limited.

## Contribution

The paper is the first to investigate the protective role of fullerene C60 derivatives against zinc toxicity in cucumber plants.

## Key findings

- Fullerene C60 derivatives partially mitigated growth reduction and leaf chlorosis caused by zinc stress.
- The compounds altered the abundance of some Zn-related metabolites, suggesting a potential antioxidant effect.
- However, fullerenes did not reduce zinc transport from roots to shoots or significantly adsorb zinc.

## Abstract

Zinc (Zn) in excess is very toxic for plants and can limit agriculture. Carbon-based engineered nanomaterials with high electron mobility and electron-accepting capability may be essential for mitigating heavy metal stress. In the present study, the protective role of some fullerene C60 derivatives (fullerenol [C60(OH)22–24] and the arginine C60 [C60(C6H13N4O2)8H8]) were tested for the first time against Zn toxicity in Cucumis sativus L. (cucumber). Plants were grown hydroponically at three concentrations of fullerenes (0, 2, and 10 mg L−1) without or with 40 µM Zn for 17 days. Plant growth, leaf chlorosis, and nutritional imbalances in combination with a metabolomics approach were analyzed. The Zn-treated plants show chlorotic leaves, the retarded growth of shoots (−20%), and roots (−49%) and nutrient imbalance. Addition of fullerene C60 derivatives suppressed loss in the dry biomass of leaves (15%) and roots (40%; fullerenol only) induced by high Zn. However, they did not alter leaf chlorophyll, shoot dry biomass, and elemental composition, including leaf Zn. Moreover, the Zn of xylem sup from roots remained unchanged by fullerenes. In an adsorption experiment, the amounts of Zn adsorbed by tested C60 were below the detection limits. The addition of C60 derivatives slightly changed the metabolite profiling in stressed plants. Nevertheless, in fullerene-treated plants, the abundance of some Zn-responsible metabolites tended to be altered in the opposite direction as compared with the metabolic responses to excessive Zn alone. There were several up-regulated metabolites protecting plants under oxidative stress. We speculate that fullerene C60 derivatives have the ability to increase antioxidant non-enzyme activity at least, improving some growth parameters. However, fullerenes did not reduce Zn transport from the root to the shoots. We concluded that the low capacity of these compounds to buffer Zn in the root zone might limit the efficiency of fullerene derivatives against Zn toxicity. Our results provide new evidence for the crucial role of Zn–fullerene interactions in the amelioration of Zn toxicity in plants.