Impact of nano-CuO stress on rice (Oryza sativa L.) seedlings Arun Kumar Shaw, Zahed Hossain ⇑ Plant Stress Biology Lab, Department of Botany, West Bengal State University, Kolkata 700 126, West Bengal, India highlights  The present study highlights the response of rice seedlings to nano-CuO stress.  Stress induced modulation of antioxidant enzymes and metabolites were studied.  Histochemical staining with NBT and DAB indicate severe oxidative burst.  Elevated APX and GR activity do not protect stressed cells from oxidative damage.  Decline in DHAR renders stressed cells in futile recycling of ascorbate pool. article info Article history: Received 1 February 2013 Received in revised form 16 May 2013 Accepted 19 May 2013 Available online xxxx Keywords: Antioxidant Nano-CuO stress Nanoparticles Nanotoxicology Rice ROS abstract Indiscriminate release of metal oxide nanoparticles (NPs) into the environment due to anthropogenic activities has become a serious threat to the ecological system including plants. The present study assesses the toxicity of nano-CuO on rice (Oryza sativa cv. Swarna) seedlings. Three different levels of stress (0.5 mM, 1.0 mM and 1.5 mM suspensions of copper II oxide, <50 nm particle size) were imposed and seedling growth performance was studied along control at 7 and 14 d of experiment. Modulation of ascorbate–glutathione cycle, membrane damage, in vivo ROS detection, foliar H 2 O 2 and proline accumu- lation under nano-CuO stress were investigated in detail to get an overview of nano-stress response of rice. Seed germination percentage was significantly reduced under stress. Higher uptake of Evans blue by nano-CuO stressed roots over control indicates loss of root cells viability. Presence of dark blue and deep brown spots on leaves evident after histochemical staining with NBT and DAB respectively indicate severe oxidative burst under nano-copper stress. APX activity was found to be significantly increased in 1.0 and 1.5 mM CuO treatments. Nevertheless, elevated APX activity might be insufficient to scavenge all H 2 O 2 produced in excess under nano-CuO stress. That may be the reason why stressed leaves accumu- lated significantly higher H 2 O 2 instead of having enhanced APX activity. In addition, increased GR activity coupled with isolated increase in GSH/GSSG ratio does not seem to prevent cells from oxidative damages, as evident from higher MDA level in leaves of nano-CuO stressed seedlings over control. Enhanced proline accumulation also does not give much protection against nano-CuO stress. Decline in carotenoids level might be another determining factor of meager performance of rice seedlings in combating nano-CuO stress induced oxidative damages. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Indiscriminate release of metal oxide nanoparticles (NPs) into the environment due to anthropogenic activities has become a serious threat to the ecological system including plants. Plant nanotoxicology is an emerging and less-explored area of research for the plant stress biologists. By definition, nanoparticles (NPs) are ultrafine particles that typically have at least one dimension less than 100 nm in size. Apart from its wide applications in drug and gene delivery, tissue engineering, bio-detection of pathogens and tumour therapy, NPs are also known to be toxic for biological systems including plants. The negative impacts of NPs on plant development and metabolism depend on the size, concentration and chemistry of NPs, as well as the chemical milieu of the subcel- lular sites to which the NPs are deposited (Dietz and Herth, 2011). Uptake of NPs through primary roots is usually barred due to presence of suberinized exo- and endodermis. However, lateral root junctions are the primary sites through which NPs could enter the xylem via cortex and the central cylinder (Dietz and Herth, 2011). NPs upon dissolution act as metal ions, able to interact with 0045-6535/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2013.05.044 Abbreviations: DAB, 3 0 3 0 -diaminobenzidine; GSH, reduced glutathione; GSSG, oxidized glutathione; MDA, malondialdehyde; NBT, nitro blue tetrazolium; NPs, nanoparticles; ROS, reactive oxygen species. ⇑ Corresponding author. Tel.: +91 33 25241975; fax: +91 33 2524 1977. E-mail address: zahed_kly@yahoo.com (Z. Hossain). Chemosphere xxx (2013) xxx–xxx Contents lists available at SciVerse ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere Please cite this article in press as: Shaw, A.K., Hossain, Z. Impact of nano-CuO stress on rice (Oryza sativa L.) seedlings. Chemosphere (2013), http:// dx.doi.org/10.1016/j.chemosphere.2013.05.044