Zinc Uptake, Photosynthetic Efficiency and Oxidative Stress in the Seagrass Cymodocea nodosa Exposed to ZnO Nanoparticles

Paraskevi Malea; Katerina Charitonidou; Ilektra Sperdouli; Zoi Mylona; Michael Moustakas

doi:10.3390/ma12132101

Zinc Uptake, Photosynthetic Efficiency and Oxidative Stress in the Seagrass Cymodocea nodosa Exposed to ZnO Nanoparticles

Materials (Basel). 2019 Jun 29;12(13):2101. doi: 10.3390/ma12132101.

Authors

Paraskevi Malea¹, Katerina Charitonidou^{1

2}, Ilektra Sperdouli^{1

3}, Zoi Mylona¹, Michael Moustakas⁴

Affiliations

¹ Department of Botany, Aristotle University of Thessaloniki, GR-54124 Thessaloniki, Greece.
² School of Agricultural Sciences, University of Thessaly, GR-38446 Volos, Greece.
³ Institute of Plant Breeding and Genetic Resources, Hellenic Agricultural Organisation-Demeter, Thermi, GR-57001 Thessaloniki, Greece.
⁴ Department of Botany, Aristotle University of Thessaloniki, GR-54124 Thessaloniki, Greece. moustak@bio.auth.gr.

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 (Φ_NO). 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.

Keywords: adaptive response; hormetic response; hydrogen peroxide; marine angiosperms; non-photochemical quenching; photoprotective mechanism; plastoquinone pool; reactive oxygen species (ROS); redox state; zinc oxide nanoparticles.