Translocation of Nano-Gold, -Silver and -copper in Calendula officinalis L. Tissues under foliar exposure

Abstract

Nanosized materials contribute significantly to modern industry and agriculture, with both beneficial and potentially adverse effects on plant systems. This study investigated the capacity of Calendula officinalis L. to accumulate and translocate gold (AuNPs), silver (AgNPs), and copper (CuNPs) nanoparticles applied by foliar spraying over a 28-day period, at concentrations ranging from 1 to 100 mg/L. Metal accumulation in plant tissues and soil was quantified using atomic absorption and optical emission spectrometry. The highest accumulation occurred for gold nanoparticles, reaching up to 143 mg/kg in leaves and 94 mg/kg in stems. In comparison, copper and silver levels in plant tissues remained below 50 mg/kg. Notably, CuNP treatments led to a concentration-dependent decrease in copper content in both roots and soil, while AuNPs and AgNPs increased their respective concentrations in these compartments—likely due to interactions with root exudates affecting rhizosphere dynamics. Physiological responses of calendula leaves varied depending on nanoparticle type and dose. Low concentrations (1–10 mg/L) generally stimulated or maintained photosynthetic pigment levels, antioxidant activity, and phenolic compound content. However, higher concentrations (50–100 mg/L) tended to inhibit pigment accumulation and modify antioxidant and phenolic profiles. Gold and silver NPs mostly enhanced antioxidant activity, whereas copper NPs induced a more variable response depending on dosage. These findings highlight the complex interplay between nanoparticle characteristics and plant physiology, and underline the necessity of precise dosage control when considering the application of metal nanoparticles in agricultural contexts.