Metal-catalyzed protein tyrosine nitration in biological systems

Abstract

Protein tyrosine nitration is an oxidative postranslational modification that can affect protein structure and function. It is mediated in vivo by the production of nitric oxide-derived reactive nitrogen species (RNS), including peroxynitrite (ONOO^?) and nitrogen dioxide (^?NO₂). Redox-active transition metals such as iron (Fe), copper (Cu), and manganese (Mn) can actively participate in the processes of tyrosine nitration in biological systems, as they catalyze the production of both reactive oxygen species and RNS, enhance nitration yields and provide site-specificity to this process. Early after the discovery that protein tyrosine nitration can occur under biologically relevant conditions, it was shown that some low molecular weight transition-metal centers and metalloproteins could promote peroxynitrite-dependent nitration. Later studies showed that nitration could be achieved by peroxynitrite-independent routes as well, depending on the transition metal-catalyzed oxidation of nitrite (NO₂^?) to ^?NO₂ in the presence of hydrogen peroxide. Processes like these can be achieved either by hemeperoxidase-dependent reactions or by ferrous and cuprous ions through Fenton-type chemistry. Besides the in vitro evidence, there are now several in vivo studies that support the close relationship between transition metal levels and protein tyrosine nitration. So, the contribution of transition metals to the levels of tyrosine nitrated proteins observed under basal conditions and, specially, in disease states related with high levels of these metal ions, seems to be quite clear. Altogether, current evidence unambiguously supports a central role of transition metals in determining the extent and selectivity of protein tyrosine nitration mediated both by peroxynitrite-dependent and independent mechanisms.     

Plant microbiota modified by plant domestication

Human life became largely dependent on agricultural products after distinct crop-domestication events occurred around 10,000 years ago in different geographical sites. Domestication selected suitable plants for human agricultural practices with unexpected consequences on plant microbiota, which has notable effects on plant growth and health. Among other traits, domestication has changed root architecture, exudation, or defense responses that could have modified plant microbiota. Here we present the comparison of reported data on the microbiota from widely consumed cereals and legumes and their ancestors showing that different bacteria were found in domesticated and wild plant microbiomes in some cases. Considering the large variability in plant microbiota, adequate sampling efforts and function-based approaches are needed to further support differences between the microbiota from wild and domesticated plants. The study of wild plant microbiomes could provide a valuable resource of unexploited beneficial bacteria for crops.     

Change in the H2 photoproduction capability in a synchronously grown aerobic nitrogen-fixing cyanobacterium,Synechococcus sp. Miami BG 043511

Synchronously growing cells of nitrogen-fixing Synechococcus sp. Miami BG 043511 were harvested periodically and the capability for hydrogen photoproduction in closed vessels was measured under hydrogen production conditions. The capability for hydrogen photoproduction in cells was correlated with that of cellular carbohydrate content. Cells with a high carbohydrate content exhibited a high capacity for hydrogen production and those with low carbohydrate content exhibited low capacity for hydrogen production. Nitrogenase activity at the onset of incubation did not coincide with a capability for the cells to produce hydrogen during the subsequent incubation period. Interestingly, when cells with a high capacity for hydrogen photoaccumulation were incubated, alternate periods of hydrogen and oxygen accumulation were observed at 12 hour intervals. About 0.5 ml of hydrogen per ml of cell suspension was accumulated in flasks during the initial 12-h incubation period. These observations indicate that the use of synchronous culture can be one of the ways of provide materials suitable not only for basic studies but also for applied aspects of hydrogen photoproduction.     

Competition between heather and grasses on Scottish moorlands: Interacting effects of nutrient enrichment and grazing regime

Abstract. Considerable losses and degradation of heathlands (in moorlands and lowlands) have been reported across Europe, with Calluna vulgaris (heather) being replaced by other species, often grasses. Increasing atmospheric nitrogen deposition and overgrazing have been suggested as the driving factors behind this change. This possibility was investigated in a study of the interacting effects of nutrient inputs and grazing on heather and three grass species (Nardus stricta, Deschampsia cespitosa and D. flexuosa) in the field, on a moorland in northeastern Scotland. In addition, the interacting effects of increasing nutrients and Calluna canopy height on N. stricta and D. cespitosa were studied using turves in an outdoor experimental area. In the field, fencing had a larger effect than fertilizer on the growth of all species, except for N. stricta, the species most unpalatable to herbivores. Fencing led to an increase in the height of the Calluna canopy, which may reduce light availability for the grasses. In the turf experiment, the height of the Calluna canopy affected the diameter of the grass tussocks and percentage of green matter (i.e. live leaf material), with plants under the more closed Calluna canopies being smaller. This study suggests that the slow‐growing, evergreen Calluna is a more effective competitor than the faster growing grasses when it has a tall, intact canopy, even at increased levels of nutrient supply. However, overgrazing promotes gap formation in the Calluna canopy, providing an opportunity for grasses to take advantage of increased nutrients. Thus the conservation of heather moorlands requires an understanding of the grazing level which allows Calluna to maintain sufficient canopy structure to outcompete grasses for light.     

Tannin,nitrogen, and cell wall composition of green vs. senescent Douglas-fir foliage

Summary Tannin, cell wall, and nitrogen composition of green foliage and needle litter of similar-aged Douglas-fir (Pseudotsuga menziesii Mirb. Franco) from two stands differing in density and crown closure were compared. Trees in the closed-canopy stand had a lower basal area growth rate than those in the open-canopy stand. Stands did not differ in wood basal area/ha or forest floor C/N ratios, but the closed-canopy stand had a significantly larger accumulation of forest floor biomass and significantly higher levels of field-extractable nitrogen and nitrogen mineralization rates. Green foliage from trees in the closed-canopy stand had significantly lower nitrogen, astringency, and lignin contents, but higher cellulose concentration than trees in the open-canopy stand. These trends, inconsistent with the inverse relationship often observed between nitrogen and polyphenol contents of foliage, may result from differences in relative resource availability in the two stands. In contrast to green foliage, needle litter from the two stands had comparable contents of nitrogen, cellulose, and lignin, but astringency was significantly higher in litter from the closed-canopy stand. It is suggested that, within the constraints imposed by site conditions, evergreens may alter the tannin composition of senescing foliage, potentially affecting herbivory and decomposition differently.     

Strategies for farmers and policy makers to control nitro-gen losses whilst maintaining crop production

The nitrogen (N) cycle is essentially 'leaky'. The losses of small amounts of nitrate to waters and of ammonia and nitrous oxide to the atmosphere are a part of the global biogeo-chemical N cycle. However, intensive agricultural production, industry and vehicle use have more than doubled the amount of 'reactive' N in the environment, resulting in eutrophication, ecosystem change and health concerns. Research has identified agricultural practices that cause large losses of N and, in some cases, developed solutions. This paper discusses the problems of maintaining productivity while reducing N losses, compares conventional with low input (integrated) and organic farming systems, and discusses wider options. It also looks at the need to integrate studies on N with other environmental impacts, set in the context of the whole farm system, to provide truly sustainable agricultural systems.     

Nodulation and N2 fixation byInga jinicuil,a woody legume in coffee plantations

Summary Nodule biomass and yearly C₂H₂ reduction rates are reported forInga jinicuil, a leguminous tree used for shade in Mexican coffee plantations. Annual fixation by this species approximates 35 kg ha^–1; which, when compared to nitrogen additions from fertilizers, represents an important nitrogen input to the coffee ecosystem.     

A further extension of the method for independently measuring the amount of nitrogen fixed by a legume crop

Summary The combination of using¹⁵N for determining the amount of nitrogen fixed by a legume crop in field experiments and the labelling of only one treatment at a time in each treatment combination is shown to be conceptually and experimentally valid for determining the effect of cultural practices on the amount of nitrogen fixed by a legume crop.     

Sensitivity of the woodland herb Anemone hepatica to changing environmental conditions

Abstract. The decline of deciduous woodland populations of Anemone hepatica L. in southern Sweden is documented and possible causes are discussed. The study was based on (1) re‐investigations of 6.25 km² grid‐squares first studied in 1938–1970, (2) distribution of A. hepatica in woodland sites with well‐known soil chemical properties and (3) a detailed study over 12 consecutive years into the relationships between biological characteristics of the species (number of individuals, vegetative development, flowering frequency) and environmental variables (temperature, precipitation), soil chemistry and time. There was a close relationship between soil acidity (pH, solubility of Al³⁺) and both distribution and biological characteristics. The biological variables declined significantly over time but were not related to climatic variability. Increasing soil acidity and Al³⁺ solubility are concluded to be the main factors responsible for the decline of A. hepatica in S. Swedish deciduous woodlands.     

Micronutrient availability to cereals from calcareous soils

Summary The mechanism of higher grain production of wheat (Triticum aestivum L.) by four tillage methods was explored on a sandy calcareous soil of Sahl-Al Jafara, Libya, during the year 1976–77. Tillage methods increased grain yield and dry matter weight at the boot stage in the order of no-tillage<rotovator=disc plough < subsoiler. Rotovation to 15 cm and disc ploughing to 25 cm depth enhanced grain production mainly by eliminating weed competition. In both the cases, roots penetrated < 25 cm where plough-pan existed.Further yield increases by 50 cm deep subsoiling seems to be mainly explained by N and Cu rise in plants from their marginal to optimum levels and by reduction of Mn deficiency in plant shoots. Penetration of roots beyond the 25 cm plough-pan apparently resulted in higher absorption of these nutrients from leached or native soil supplies. Subsoiling also resulted in greater Zn concentration in plant shoots which, under marginal to deficient conditions, will also increase grain production.