Nitrate supply decreases fermentation and alleviates oxidative and ionic stress in nitrogen-fixing soybean exposed to saline waterlogging.

Nitrate (NO3 - ) nutrition is known to mitigate the damages caused by individual stresses of waterlogging and salinity. Here, we investigated the role of NO3 - in soybean plants exposed to these stresses in combination. Nodulated soybean cultivated under greenhouse conditions and daily fertilised with a nutrient solution without nitrogen were subjected to the following treatments: Water, NO3 - , NaCl, and NaCl+NO3 - . Then, plants were exposed to waterlogging (6days) and drainage (2days). Compared to plants exposed to isolated stress, the saline waterlogging resulted in higher concentrations of H2 O2 , O2 ˙- , and lipid peroxidation at the whole-plant level, mainly during drainage. Furthermore, saline waterlogging increased fermentation and the concentrations of Na+ and K+ in roots and leaves both during waterlogging and drainage. NO3 - supplementation led to augments in NO3 - and NO levels, and stimulated nitrate reductase activity in both organs. In addition, NO3 - nutrition alleviated oxidative stress and fermentation besides increasing the K+ /Na+ ratio in plants exposed to saline waterlogging. In conclusion, NO3 - supplementation is a useful strategy to help soybean plants overcome saline waterlogging stress. These findings are of high relevance for agriculture as soybean is an important commodity and has been cultivated in areas prone to saline waterlogging.

Waterlogging priming alleviates the oxidative damage, carbohydrate consumption, and yield loss in soybean (Glycine max) plants exposed to waterlogging.

In this study, we tested whether waterlogging priming at the vegetative stage would mitigate a subsequent waterlogging event at the reproductive stage in soybean [Glycine max (L.) Merr.]. Plants (V3 stage) were subjected to priming for 7days and then exposed to waterlogging stress for 5days (R2 stage) with non-primed plants. Roots and leaves were sampled on the fifth day of waterlogging and the second and fifth days of reoxygenation. Overall, priming decreased the H2 O2 concentration and lipid peroxidation in roots and leaves during waterlogging and reoxygenation. Priming also decreased the activity of antioxidative enzymes in roots and leaves and increased the foliar concentration of phenols and photosynthetic pigments. Additionally, priming decreased fermentation and alanine aminotransferase activity during waterlogging and reoxygenation. Finally, priming increased the concentration of amino acids, sucrose, and total soluble sugars in roots and leaves during waterlogging and reoxygenation. Thus, primed plants were higher and more productive than non-primed plants. Our study shows that priming alleviates oxidative stress, fermentation, and carbohydrate consumption in parallel to increase the yield of soybean plants exposed to waterlogging and reoxygenation.

Iron toxicity increases oxidative stress and impairs mineral accumulation and leaf gas exchange in soybean plants during hypoxia.

Iron toxicity is a major challenge faced by plants in hypoxic soils; however, the consequences of such combined stress for soybean (Glycine max) remain to be determined. Here we assessed the physiological responses of soybean plants exposed to hypoxia and a high concentration of iron. Soil-grown plants cultivated in a greenhouse until the vegetative stage were transferred to a hydroponic system containing nutrient solution and subjected to two oxygen conditions (normoxia (6.2 mg L-1) and hypoxia (0.33 mg L-1)) and two iron concentrations (Fe-EDTA) (0.09 and 1.8 mM) for 72 h. During hypoxia, high concentrations of iron in the nutrient solution resulted in increased iron accumulation in roots and leaves. Under this condition, the concentrations of zinc, nitrogen, potassium, and calcium decreased in the roots, while the concentration of nitrogen and magnesium decreased in the leaves. Additionally, during hypoxia, the higher concentration of iron led to an increase in the activity of the antioxidant enzymes in roots and leaves, while decreased the levels of the photosynthetic pigments, leaf gas exchange, and plant growth. In conclusion, high iron concentration in the root medium results in a considerably more severe damage condition to soybean plants under hypoxia compared to plants grown under low iron availability.

Tolerance of Landoltia punctata to arsenate: an evaluation of the potential use in phytoremediation programs.

Plants used in phytoremediation should accumulate and tolerate a specific pollutant. Here, we aimed at evaluating a possible arsenic (As) accumulation and mechanisms of tolerance against As-induced damage in Landoltia punctata to explore this species for phytoremediation. Plants were subjected to increasing As levels. As absorption was higher with increasing As levels. The activity of superoxide dismutase and glutathione reductase as well as anthocyanin levels increased with As levels. Catalase and peroxidase activities increased in plants subjected to As levels up to 1.0 mg L-1 and decreased at higher levels. Due to the antioxidant system, higher levels of reactive oxygen species were restrained in plants under low levels of As. However, the levels of superoxide anion, hydrogen peroxide, and lipid peroxidation increased in response to the impaired antioxidant system induced by the highest As levels. Biomass decreased in plants exposed to As and scanning electron microscopy revealed root structural damage in the root cap of plants under 3.0 mg L-1 As. This work highlights that L. punctata can be considered a hyperaccumulator species and has potential for As phytoremediation when levels are lower than 1.0 mg L-1-a concentration 100-fold higher than that recommended for drinking water. Novelty Statement: Landoltia punctata can be considered a hyperaccumulator species and has the potential for arsenic phytoremediation when levels are lower than 1.0 mg L-1.

Does oxidative stress determine the thermal limits of the regeneration niche of Vriesea friburgensis and Alcantarea imperialis (Bromeliaceae) seedlings?

The predicted environmental changes may be detrimental to initial seedling growth, particularly the expected increase in air temperature. We therefore investigated the thermal limits for growth and development of Vriesea friburgensis and Alcantarea imperialis seedlings in the context of oxidative stress. The optimal temperatures for the growth of V. friburgensis and A. imperialis were 25 and 25-30 °C, respectively. Extreme temperatures (15, 30, or 35 °C) induced oxidative stress in both species with significant accumulation of hydrogen peroxide (H2O2) and nitric oxide (NO). Under oxidative stress, the amount of chlorophyll decreased in both species, more prominently in V. friburgensis, while carotenoid levels dramatically increased in A. imperialis. Notably, the activities of superoxide dismutase, catalase (CAT), and ascorbate peroxidase increased in A. imperialis at extreme temperatures. Similar results were observed for V. friburgensis; however, the activity of CAT remained unaffected regardless of temperature. Seedlings of A. imperialis survived at a wider range of temperatures than V. friburgensis, which had greater than 40% mortality when growing at 30 °C. Overall, precise control of cellular H2O2 and NO levels takes place during the establishment of A. imperialis seedlings, allowing the species to cope with relatively high temperatures. The thermal limits of the fundamental niches of the species investigated, determined based on the ability of seedlings to cope with oxidative stress, were distinct from the realized niches of these species. The results suggest that recruitment success is dependent on the ability of seedlings to handle extreme temperature-triggered oxidative stress, which limits the regeneration niche.

Salinity-induced accumulation of endogenous H2S and NO is associated with modulation of the antioxidant and redox defense systems in Nicotiana tabacum L. cv. Havana.

Salinity is one of the abiotic factors that most affect crop growth and production. This study focused on the effect of high salinity on the endogenous levels of the signaling molecules hydrogen sulfite (H2S) and nitric oxide (NO) in Nicotiana tabacum leaves and the extent of these for the biochemically-driven plant tolerance to such abiotic stress. The NaCl treatment for 10days led to an expressive augment of H2S and NO levels. This increase was correlated with the raise of l-Cys and l-Arg and the induction of l-cysteine desulfhydrase, cyanoalanine synthase, cysteine synthase, nitrate reductase and arginase, enzymes known to be involved in the biosynthesis of H2S or NO. The enzymatic antioxidant system (superoxide dismutase and catalase activity) was boosted and the non-enzymatic antioxidant glutathione was intensively oxidized in leaves upon stress allowing plants to cope with oxidative stress. Lower stomatal conductance was observed in stressed plants in comparison with control ones. Moreover, the high activity of antioxidant enzymes and high rate of glutathione oxidation following salt stress were considerably decreased upon NO or H2S scavenging. Thus, increment in NO and H2S levels and their interplay, along with metabolic and physiological changes, contributed to tobacco survival to extreme salinity conditions.

Quinolines: Microwave-assisted synthesis and their antifungal, anticancer and radical scavenger properties.

An efficient method for the synthesis of quinolines using microwave irradiation was developed providing 28 quinolines with good yields. The reaction procedures are environmentally friendly, convenient, mild and of easy work-up. Quinolines were evaluated for their antifungal, anticancer and antioxidant properties and exhibited high activities in all tests performed.