Nitric oxide alleviates wheat yield reduction by protecting photosynthetic system from oxidation of ozone pollution * Caihong Li a , Yanjie Song a, b , Liyue Guo a , Xian Gu a, b , Mahmud A. Muminov c , Tianzuo Wang a, b, * a State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, The Chinese Academy of Sciences, Beijing 100093, PR China b College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, PR China c Laboratory of Environmental Problems, Samarkand State University, Samarkand, Uzbekistan article info Article history: Received 27 September 2017 Received in revised form 25 January 2018 Accepted 28 January 2018 Keywords: Nitric oxide Ozone Wheat (Triticum aestivum) Reactive oxygen species Grain yield abstract Accelerated industrialization has been increasing releases of chemical precursors of ozone. Ozone con- centration has risen nowadays, and it's predicted that this trend will continue in the next few decades. The yield of many ozone-sensitive crops suffers seriously from ozone pollution, and there are abundant reports exploring the damage mechanisms of ozone to these crops, such as winter wheat. However, little is known on how to alleviate these negative impacts to increase grain production under elevated ozone. Nitric oxide, as a bioactive gaseous, mediates a variety of physiological processes and plays a central role in response to biotic and abiotic stresses. In the present study, the accumulation of endogenous nitric oxide in wheat leaves was found to increase in response to ozone. To study the functions of nitric oxide, its precursor sodium nitroprusside was spayed to wheat leaves under ozone pollution. Wheat leaves spayed with sodium nitroprusside accumulated less hydrogen peroxide, malondialdehyde and electro- lyte leakage under ozone pollution, which can be accounted for by the higher activities of superoxide dismutase and peroxidase than in leaves treated without sodium nitroprusside. Consequently, net photosynthetic rate of wheat treated using sodium nitroprusside was much higher, and yield reduction was alleviated under ozone fumigation. These findings are important for our understanding of the po- tential roles of nitric oxide in responses of crops in general and wheat in particular to ozone pollution, and provide a viable method to mitigate the detrimental effects on crop production induced by ozone pollution, which is valuable for keeping food security worldwide. © 2018 Elsevier Ltd. All rights reserved. 1. Introduction Ground-level ozone (O 3 ) is recognized as one of the most deleterious rural air pollutants due to its powerful oxidization and phytotoxicity (Fiore et al., 2012; Li and Blande, 2015; Carriero et al., 2016). After entering the 21st century, O 3 concentrations are increasing at a rate of approximately 0.5e2% per year over the northern mid-latitudes (Intergovernmental Panel on Climate Change, 2013). The rapid process of urbanization and industriali- zation is inevitably releasing more and more chemical precursors of O 3 , and leading to rising O 3 concentrations worldwide (Sitch et al., 2007; Wang et al., 2007). In addition to being a greenhouse gas and harmful to human health, potential impacts of ozone on agriculture are larger than the direct impacts of climate change in some re- gions, with predicted up to 26% of global annual yield reductions for some crops by 2030 (Avnery et al., 2011b). Take wheat as an instance, published documents showed that ozone resulted in 6.4e14.9% of yield loss now, and this number would rise to 14.8e23.0% by 2020 (Feng et al., 2015). Wheat is one of the most vital crops worldwide, and more than half of the world population relies on it as their primary principal food (Zhu et al., 2011; Saitanis et al., 2014; Li et al., 2016). It was estimated that global yield of wheat must increase constantly by 2% annually until 2020 to satisfy the requirements driven by growing human population and prosperity (Singh et al., 2007). Moreover, growing human population on earth means that the food demands will increase for more than 40 years (Godfray et al., 2010). However, * This paper has been recommended for acceptance by Klaus Kummerer. * Corresponding author. State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, the Chinese Academy of Sciences, Beijing 100093, PR China. E-mail address: tzwang@ibcas.ac.cn (T. Wang). Contents lists available at ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol https://doi.org/10.1016/j.envpol.2018.01.093 0269-7491/© 2018 Elsevier Ltd. All rights reserved. Environmental Pollution 236 (2018) 296e303