Effects of Ambient Oxygen and of Fixed Nitrogen on Concentrations of Glutathione, Ascrobate, and Associated Enzymes in Soybean Root Nodules

Abstract

Soybean (Glycine max [L.] Merr.) root nodules contain the enzymes of the ascorbate-glutathione cycle for defense against activated forms of oxygen. Nodulated roots of hydroponically grown soybean plants were exposed to atmospheres containing 2, 21, 50, or alternating 21 and 50 kilopascals of 02. The activities of ascorbate (ASC) peroxidase, monodehydroascorbate (MDHA) reductase, dehydroascorbate (DHA) reductase, and glutathione (GSSG) reductase were higher in nodules exposed to high P02.Nodule contents of ascorbate and reduced glutathione were also greater in the high P02 treatments. Treatment of modulated plants with fixed nitrogen (urea) led to concomitant decreases in acetylene reduction activity, in leghemoglobin content, and in activities of ASC peroxidase, DHA reductase, and GSSG reductase. Activity of MDHA reductase and glutathione concentrations in nodules were not affected by treatment with urea. The enzymes of the ascorbate-glutathione cycle were also detected in uninfected soybean roots, although at levels substantially below those in nodules. These observations indicate that the ascorbate-glutathione cycle can adjust to varying physiological conditions in nodules and that there is a key link between N2 fixation and defenses against activated forms of oxygen.The oxygen relations of legume root nodules are extremely important in maintaining normal nodule functions. There are many aspects to the relationship between oxygen and N2 fixation in nodules. The essential role of leghemoglobin as a 02-binding protein and the 02 sensitivity of nitrogenase have long been recognized as fundamentally important factors in nodules. N2 fixation is an energy-intensive process, requiring large amounts of ATP that must be supplied by oxidative phosphorylation. Nodules have a high rate of respiratory 02 consumption, but measurements with 02 microelectrodes indicate that the P02 in nodule interior spaces is very low (24). The inner cortex of nodules presents a major impediment to 02 diffusion and is a primary factor in maintaining the low internal P02. Numerous studies utilizing flow-through gas systems for measurement of acetylene reduction and respiration have provided indirect evidence that this diffusion barrier is variable and capable of responding to gradual changes in external PO2 without damage to nitrogenase (10,

Proteins involved in biotic and abiotic stress responses as the most significant biomarkers in the ripening of Pinot Noir skins

“…Among them, it was reported the peak in the levels of ascorbate peroxidase (AsPOX), which is considered the main responsible for H 2 O 2 removal in plant cytosol, mitochondria, and chloroplasts (Dalton et al 1991;Chew et al 2003). In agreement with these results, we identified a spot corresponding to AsPOX (spot 2677) showing opposite coefficients for RS35 and RS38 models, reflecting the decreasing trend that we observed though the progression of ripening (Fig.…”

Effects of exogenous application and stem infusion of ascorbate on soybean (Glycine max) root nodules

“…Activity of DHA reductase was determined by following the decrease in A $%! due to the oxidation of NADH in reaction mixtures as described by Dalton et al (1991). Measurements of total protein concentration in extracts were performed as described by Bradford (1976) with BSA as the standard.…”

“…The macerate was centrifuged for 15 min at 12000 g. Activity of ASC peroxidase was determined in the supernatant by following the decrease in A #*! due to the peroxidation of ASC in reaction mixtures as described by Dalton et al (1991). Separate extracts were prepared for determination of the activity of DHA reductase.…”

Cloning and characterization of the katA gene of Rhizobium meliloti encoding a hydrogen peroxide-inducible catalase

“…The symbiosis is mainly characterized by its ability to fix atmospheric nitrogen, and the key enzyme of this process, the nitrogenase located in the microsymbiont, is rapidly and irreversibly inactivated by oxygen; the possible role of oxygen-derived species in this inactivation is still an open question (40). Nodules have a high potential to produce damaging oxygen-derived species such as hydrogen peroxide because of the strong reducing conditions required for nitrogen fixation and the action of several proteins, including ferredoxin, uricase, hydrogenase, and leghemoglobin (12). This hemoprotein, present in large amounts in legume nodules, is itself subject to an autoxidation process, generating superoxide anion and hydrogen peroxide (41).…”