Abstract
ABSTRACT: In this work, we compared nitrate-supplied plants (non-nodulated) with non-nitrate-supplied plants (nodulated) under oxygen privation of root system (hypoxia) and re-oxygenation (post-hypoxia; recovery) in order to verify whether N sources affect the antioxidant system during oxidative stress caused by hypoxia and post-hypoxia conditions. Antioxidant enzymatic activities, ascorbate redox state, and reactive oxygen species (ROS) levels were analyzed in roots and leaves of two soybean genotypes, Fundacep 53 RR and BRS Macota at reproductive stage R2, during hypoxia and post-hypoxia in an experiment carried out in a hydroponic system. The antioxidant system was strongly induced in roots of nitrate-supplied plants of both genotypes, with high activity of superoxide dismutase, ascorbate peroxidase, catalase, glutathione reductase and guayacol peroxidase. It also increased reduced ascorbate and ascorbate redox state and decreased ROS production under hypoxia and recovery, while in leaves of nodulated and non-nodulated plants, a slight increase on antioxidant system was observed. Nitrate may benefit soybean plants under hypoxic conditions and subsequent re-oxygenation by inducing the antioxidant system mainly in roots to cope with ROS production and reduce oxidative damage.
Highlights
Waterlogging, or flooding, causes oxygen deprivation to plant roots (Limami et al, 2014) and leads to inhibition of mitochondrial oxidative phosphorylation and decrease in ATP production (van Dongen and Licausi, 2015)
The beneficial effects of nitrate have been attributed to nitric oxide (NO) production via the nitrate reductase activity in cytosol and within mitochondria via cytochrome c oxidase (COX) (Gupta and Igamberdiev, 2011)
Antioxidant enzymatic activity The antioxidant enzymatic system of plants subjected to hypoxia and subsequent re-oxygenation are shown in roots (Figures 1A, B, C, D, E and F and 3A, B, C, D, E and F) and leaves
Summary
Waterlogging, or flooding, causes oxygen deprivation to plant roots (Limami et al, 2014) and leads to inhibition of mitochondrial oxidative phosphorylation and decrease in ATP production (van Dongen and Licausi, 2015). The beneficial effects of nitrate have been attributed to nitric oxide (NO) production via the nitrate reductase activity in cytosol (van Dongen and Licausi, 2015) and within mitochondria via cytochrome c oxidase (COX) (Gupta and Igamberdiev, 2011). Most studies have shown beneficial effects of nitrate on N and C metabolism in waterlogged plants and that hypoxia followed by re-oxygenation promotes ROS production. Therefere, nitrate is supposed to be beneficial by alleviating the effects of ROS production through the induction of the antioxidative activity of enzymes to reduce oxidative damage. Superoxide dismutase (SOD) plays a key role in scavenging superoxide radical (O2−) anion into hydrogen peroxide (H2O2) (Simova-Stoilova et al, 2012)
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