Abstract
Nitric oxide (NO) is an important signaling molecule associated with many biochemical and physiological processes in plants under stressful conditions. Nitrate reductase (NR) not only mediates the reduction of NO3− to NO2− but also reduces NO2− to NO, a relevant pathway for NO production in higher plants. Herein, we hypothesized that sugarcane plants supplied with more NO3− as a source of N would produce more NO under water deficit. Such NO would reduce oxidative damage and favor photosynthetic metabolism and growth under water limiting conditions. Sugarcane plants were grown in nutrient solution and received the same amount of nitrogen, with varying nitrate:ammonium ratios (100:0 and 70:30). Plants were then grown under well-watered or water deficit conditions. Under water deficit, plants exhibited higher root [NO3−] and [NO2−] when supplied with 100% NO3−. Accordingly, the same plants also showed higher root NR activity and root NO production. We also found higher photosynthetic rates and stomatal conductance in plants supplied with more NO3−, which was associated with increased root growth. ROS accumulation was reduced due to increases in the activity of catalase in leaves and superoxide dismutase and ascorbate peroxidase in roots of plants supplied with 100% NO3− and facing water deficit. Such positive responses to water deficit were offset when a NO scavenger was supplied to the plants, thus confirming that increases in leaf gas exchange and plant growth were induced by NO. Concluding, NO3− supply is an interesting strategy for alleviating the negative effects of water deficit on sugarcane plants, increasing drought tolerance through enhanced NO production. Our data also provide insights on how plant nutrition could improve crop tolerance against abiotic stresses, such as drought.
Highlights
Nitric oxide (NO) is a diatomic radical gas and important signaling molecule in animals (Bogdan, 2015), fungi (Cánovas et al, 2016), bacteria (Crane et al, 2010), and plants (Mur et al, 2013)
Nitrite, and Ammonium We found no differences in leaf [NO3–] in plants subjected to water deficit (Figure 1A)
Root [NO3–] was significantly higher in plants supplied with 100% NO3– under water deficit when compared to plants supplied with 70% NO3– under water deficit (Figure 1B)
Summary
Nitric oxide (NO) is a diatomic radical gas and important signaling molecule in animals (Bogdan, 2015), fungi (Cánovas et al, 2016), bacteria (Crane et al, 2010), and plants (Mur et al, 2013). In plants, increasing evidence indicates NO as a key component of the signaling network, controlling numerous physiological and metabolic processes such as seed germination (Albertos et al, 2015), flowering (He et al, 2004), root growth (Fernandez-Marcos et al, 2011), respiration, stomatal conductance (Moreau et al, 2010; Wang et al, 2015), and adaptive responses to biotic and abiotic stresses (Shan et al, 2015; Fatma et al, 2016). NO synthesis is increased in plants under drought and its role in promoting acclimation responses to cope with water deficit has been suggested (Cai et al, 2015; Silveira et al, 2017a). Spraying Snitrosogluthatione (GSNO)—a NO donor—on sugarcane plants resulted in higher photosynthesis under drought, promoting plant growth under stressful condition (Silveira et al, 2016)
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