Abstract
The role of nitric oxide (NO) and sulfur (S) on stomatal responses and photosynthetic performance was studied in mustard (Brassica juncea L.) in presence or absence of salt stress. The combined application of 100 μM NO (as sodium nitroprusside) and 200 mg S kg−1 soil (S) more prominently influenced stomatal behavior, photosynthetic and growth performance both in the absence and presence of salt stress. The chloroplasts from salt-stressed plants had disorganized chloroplast thylakoids, but combined application of NO and S resulted in well-developed chloroplast thylakoids and properly stacked grana. The leaves from plants receiving NO plus S exhibited lower superoxide ion accumulation under salt stress than the plants receiving NO or S. These plants also exhibited increased activity of ATP-sulfurylase (ATPS), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) and optimized NO generation that helped in minimizing oxidative stress. The enhanced S-assimilation of these plants receiving NO plus S resulted in increased production of cysteine (Cys) and reduced glutathione (GSH). These findings indicated that NO influenced photosynthesis under salt stress by regulating oxidative stress and its effects on S-assimilation, an antioxidant system and NO generation. The results suggest that NO improves photosynthetic performance of plants grown under salt stress more effectively when plants received S.
Highlights
The global aim of increasing agricultural productivity by 70% by the year 2050 for approximately 2.3 billion individuals is facing severe obstructions, primarily due to increasing abiotic stress factors (FAO, Food and Agricultural Organization, 2009)
Application of nitric oxide (NO) and S together resulted in maximum values of the above observed photosynthetic parameters in plants grown with or without salt compared to control
The positive effect of the combined treatment of NO and S was through their influence on stomatal responses, Sassimilation and the antioxidant system
Summary
The global aim of increasing agricultural productivity by 70% by the year 2050 for approximately 2.3 billion individuals is facing severe obstructions, primarily due to increasing abiotic stress factors (FAO, Food and Agricultural Organization, 2009). These factors such as cold, drought, flooding, freezing, heat, salinity, or oxidizing agents disturb plant metabolism and negatively impact productivity (Wang et al, 2004; Mian et al, 2011). Salt stress is one of the major abiotic stress factors occupying more than 45 million hectares of irrigated land (Munns and Tester, 2008) It causes excess production of reactive oxygen species (ROS) resulting in induced oxidative stress and inhibition of the Calvin-Benson cycle enzymes (Fatma et al, 2014; Nazar et al, 2014). These mechanisms are upregulation of activity of enzymatic antioxidants; ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR), and superoxide dismutase, and production of non-enzymatic antioxidants; ascorbate (AsA), reduced glutathione (GSH), carotenoids, tocopherol, Nitric Oxide Alleviates Salt Stress that help in neutralizing or scavenging ROS (Noctor et al, 2012; Khan and Khan, 2014; Nazar et al, 2015)
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