Cerium Oxide Nanoparticles Alleviate Drought Stress by Modulating Photosynthesis and Photosystem-Related Gene Expression in Barley (Hordeum vulgare L.)

Drought is an abiotic stress factor affecting crop yield and quality worldwide. Cerium oxide nanoparticles (CeO₂ NPs) or nanoceria can alleviate drought stress by modulating photosystem and gene expression. This study aims to investigate the ameliorative effects of nanoceria and possible underlying mechanisms in barley (Hordeum vulgare L.). For this purpose, barley seedlings were treated with nanoceria (50–800 mg L^-1, ~ 20 nm in diameter) under well-watered and polyethylene glycol (PEG; 10%)-induced water deficit conditions. Plant growth, biomass, pigment content, photosynthetic performance, and expression of photosystem marker genes were assessed after three weeks of treatment. PEG treatment significantly (P < 0.05) reduced growth, biomass, photosynthetic pigments (chlorophyll-a, chlorophyll-b, carotenoids), and photosystem performance (electron transport rate, maximum potential quantum efficiency of Photosystem II, and quantum yield of Photosystem II). CeO₂ NPs at 50 and 100 mg L^-1 doses significantly enhanced root and shoot length, as well as biomass. These concentrations remarkably mitigated PEG-induced reductions in growth, biomass, and photosynthetic indices. On the other side, CeO₂ NP at higher concentrations (> 200 mg L^-1) diminished this positive effect, indicating a biphasic response. Gene expression analysis revealed that while PEG treatment alone upregulated photosystem (petA, psaA, psbA, BCA) and stress (Hsp90) genes, CeO₂ NPs with PEG treatment (200 mg L^-1) decreased their expression. These findings demonstrate that nanoceria helps to ameliorate drought stress by enhancing growth and photosynthetic activity and modulating gene expression in barley.