Nano-CuO stress induced modulation of antioxidative defense and photosynthetic performance of Syrian barley (Hordeum vulgare L.)

•The present study aims to unravel the nano-CuO stress impact on Syrian barley.•Nano-stress has no significant effect on maximal quantum yield of PSII (Fv/Fm).•Histochemical DAB staining indicates severe oxidative burst under prolonged stress.•Enhanced APX activity is insufficient to enforce a light control over H2O2 level.•Concomitant decline in DHAR and MDAR results futile recycling of ascorbate pool.

Nanoparticles (NPs), a new class of pollutant has raised global environmental concern. The present study highlights the impact of nano-CuO stress on Syrian barley (Hordeum vulgare L., landrace Arabi Aswad). Seedling performances in terms of antioxidant defence and chlorophyll fluorescence were studied under three different levels of stress (0.5 mM, 1 mM and 1.5 mM suspensions of copper II oxide, <50 nm particle size, prepared in ½ MS medium) at 10 and 20 day of treatment along with control. Dose dependent reduction in shoot and root growth was recorded with passage of time. The maximal quantum yield of PS II photosynthetic apparatus (Fv/Fm) did not alter after stress application. However, performance index parameter was found to be significantly decreased irrespective of stress level and treatment period. Enhanced flavonol level with concomitant increase in APX activity found to be insufficient to enforce a light control over the H2O2 level under nano-stress. Furthermore, an impairment of the collaborative action of DHAR and MDAR in stressed leaves results in a lower ability for efficient enzymatic recycling of DHA into AsA. Overall the nano-stressed leaves exhibited significant decline in GSH/GSSG ratio that might not contribute in maintaining high GSH pool essential for sustaining balanced redox status under stress condition. In addition, an isolated increase in GR activity in 1.0 and 1.5 mM nano-CuO treated leaves at 20 day does not give much protection to the nano-CuO stressed seedlings from oxidative damages.

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