Abstract
We characterized zinc oxide nanoparticles (ZnO NPs) by dynamic light scattering (DLS) measurements, and transmission electron microscopy (TEM), while we evaluated photosystem II (PSII) responses, Zn uptake kinetics, and hydrogen peroxide (H2O2) accumulation, in C. nodosa exposed to 5 mg L−1 and 10 mg L−1 ZnO NPs for 4 h, 12 h, 24 h, 48 h and 72 h. Four h after exposure to 10 mg L−1 ZnO NPs, we noticed a disturbance of PSII functioning that became more severe after 12 h. However, after a 24 h exposure to 10 mg L−1 ZnO NPs, we observed a hormetic response, with both time and dose as the basal stress levels needed for induction of the adaptive response. This was achieved through the reduced plastoquinone (PQ) pool, at a 12 h exposure, which mediated the generation of chloroplastic H2O2; acting as a fast acclimation signaling molecule. Nevertheless, longer treatment (48 h and 72 h) resulted in decreasing the photoprotective mechanism to dissipate excess energy as heat (NPQ) and increasing the quantum yield of non-regulated energy loss (ΦNO). This increased the formation of singlet oxygen (1O2), and decreased the fraction of open reaction centers, mostly after a 72-h exposure at 10 mg L−1 ZnO NPs due to increased Zn uptake compared to 5 mg L−1.
Highlights
The small size of nanoparticles (NPs) provides them with special physical and chemical properties that are not found in bulk materials allowing their utilization, among others, in agricultural products, catalysis, cosmetics, electronics, energy production, engineering, food industry, pharmaceutics and textiles [1,2,3,4,5].Among the variety of metal NPs that are often used for marketable purposes, zinc oxide (ZnO)NPs are the most commonly used ones [6,7,8]
This increased the formation of singlet oxygen (1 O2 ), and decreased the fraction of open reaction centers, mostly after a 72-h exposure at 10 mg L−1 zinc oxide nanoparticles (ZnO NPs) due to increased Zn uptake compared to 5 mg L−1
We evaluated ZnO NPs effects on C. nodosa photosystem II (PSII) photochemistry by chlorophyll fluorescence imaging analysis, and detected reactive oxygen species (ROS) generation as a byproduct of ZnO NP’s effects, linking the ROS generation to PSII functionality
Summary
The small size of nanoparticles (NPs) provides them with special physical and chemical properties that are not found in bulk materials allowing their utilization, among others, in agricultural products, catalysis, cosmetics, electronics, energy production, engineering, food industry, pharmaceutics and textiles [1,2,3,4,5].Among the variety of metal NPs that are often used for marketable purposes, zinc oxide (ZnO)NPs are the most commonly used ones [6,7,8]. ZnO NPs, with their unique chemical and physical properties, such as high photostability, broad range of radiation absorption, high electrochemical coupling coefficient, and high chemical stability, are widely used in a diversity of applications, varying from paints to chemicals, from tires to ceramics, and from pharmaceuticals to agriculture [3,9]. An essential aspect of the risk assessment of NPs is to understand their interactions with plants, a basic component of all ecosystems [11]. Manufactured NPs are unavoidably released into the soil and through streams, rivers, and sewage treatment they reach the sea [5]. Since NPs end in aquatic ecosystems, aquatic plants may be at higher risks than terrestrial. There is a need to evaluate the risks related to NP presence in aquatic ecosystems [12]
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