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.

Production of crude xylanase from Thermoascus aurantiacus CBMAI 756 aiming the baking process.

In recent years, the baking industry has focused its attention on substituting several chemical compounds with enzymes. Enzymes that hydrolyze nonstarch polysaccharides, such as xylanase, lead to the improvement of rheological properties of dough, loaf specific volume, and crumb firmness. The purpose of this study was to find a better solid-state fermentation substrate to produce high levels of xylanase and low levels of protease and amylase, which are enzymes involved in bread quality, from Thermoascus aurantiacus CBMAI 756. Wheat bran, corncob, and corn straw were used as energy sources. The enzyme extract of corncob showed high xylanase activity (130 U/mL) and low amylase and protease activity (<1 and 15 U/mL, respectively). This enzyme profile may be more profitable for the baking industry, because it results in a slower degradation of gluten. Our results confirm this finding, because the enzyme obtained by fermentation in corncob resulted in a gluten with a higher specific volume than all the other substrates that were tested. The crude xylanase presented maximum activity at a pH of 5, and the optimum temperature was 75 °C. It was stable up to 70 °C for an hour and at a pH range from 4 to 10.

The action of glibenclamide on glycogen catabolism and related parameters in the isolated perfused rat liver.

Inhibitory effects on glycogenolysis have been reported for glibenclamide in the presence of insulin after stimulation of glycogenolysis by glucagon. Inhibition of oxidative phosphorylation, which has been equally reported for this drug, however, should stimulate glycogenolysis. The present work aimed to find an answer to the question of how glibenclamide affects glycogen catabolism in the liver of fed rats undergoing substrate- and hormone-free perfusion. The experimental system was the isolated perfused liver of ad libitum fed rats. Metabolites in the outflowing perfusate were assayed enzymatically. Oxygen uptake was measured polarographically. Glibenclamide (25-500 microM) stimulated glucose production and lactate release, with a clear correlation between concentrations and effects. Maximal stimulations were 132 and 127% for lactate production and glucose release, respectively. At low glibenclamide concentrations (up to 100 microM) both oxygen uptake and pyruvate production were stimulated, but at higher concentrations inhibition took place. Uric acid production was stimulated by glibenclamide. All effects of glibenclamide are probably due to decreases in oxidative phosphorylation. Stimulation of glucose release is the opposite of what should be expected for a hypoglycemic drug and it also contrasts with some reports of diminishing effects in the presence of glucagon plus insulin. This means that the stimulatory action on glycogenolysis that was seen as a net effect under the specific conditions of the present work could be counterbalancing inhibitory effects in vivo. This combination of events could eventually diminish the effectiveness of the drug as a hypoglycemic agent in the fed state.

Inhibition by extracellular ATP of organic anion transport in the perfused rat liver.

The action of extracellular ATP on organic anion transport in the bivascularly perfused rat liver was investigated, using bromosulfophthalein as a model substance. Transport was measured by means of the multiple-indicator dilution technique. The action of portal 100 microM ATP presented the following characteristics: (a) inhibition of bromosulfophthalein single pass extraction; the inhibition degree decreased with increasing bromosulfophthalein doses; (b) diminution of the influx rate coefficients; (c) 86.7% decrease of the maximal activity of the saturable component for bromosulfophthalein transport, but 100% increase of the non-saturable component; (d) diminution of the bromosulfophthalein flow-limited distribution space; (e) no significant alteration of the rate coefficients for metabolic sequestration. The action of ATP on organic anion transport in the intact liver occurred at much lower concentrations (10x) than those previously reported for isolated hepatocytes. This reinforces the suggestion that inhibition of organic anion transport could be a physiologically relevant effect of extracellular ATP.