Acetylene reduction,hydrogen evolution and nodule respiration in Phaseolus vulgaris

Summary In an experiment performed under greenhouse conditions, four cultivars of Phaseolus vulgaris L. (Venezuela-350; Aroana; Moruna; Carioca) were inoculated with three Rhizobium leguminosarum biovar phaseoli strains (C-05; C-40 = CIAT 255; C-89 = CIAT 55) and were fertilized with an N-free mineral nutrient solution. The plants were harvested 25, 40, and 55 days after emergence and the following paramenters were evaluated: Nitrogenase activity of nodulated roots, H₂ evolution by the nodules; relative efficiency of nitrogenase; respiration rates of nodulated roots and detached nodules; dry weight and total N of stems, leaves, pods, roots, and nodules. Generally the bean cultivar, Rhizobium strain, had an effect and there was an interaction effect with both symbiotic partners, on all parameters. On average, nodules represented 23% of total root respiration but the best symbiotic combinations showed lower ratios of C respired to N fixed. The maximum N-assimilation rate (between 40 and 55 days after emergence) of 11.93 mg N plant^–1 day^–1 occurred with the symbiotic combination of Carioca × C-05, while the poorest rate of 0.55 mg N plant^–1 day^–1 was recorded with Venezuela-350 × C-89. The best symbiotic combinations always showed the highest relative nitrogenase efficiency, but the differences in N₂-fixation rates cannot be explained solely in terms of conservation of energy by recycling of H₂. This requires further investigation.     

Integrated Sonochemical and Microbial Treatment for Decontamination of Nonylphenol-Polluted Water

Advanced oxidation processes (AOPs) are among the most efficient methods for wastewater treatment. To achieve the degradation of persistent organic pollutants (POPs), AOPs have been developed that employ Fenton reactions promoted by ultrasound (US) or microwaves (MW). Integrated methods combining AOPs with biological treatments are also of great interest. The present paper describes such an integrated approach for the decontamination of water from nonylphenol (NP), a common pollutant that accumulates in aquatic organisms and is quite resistant to biodegradation. Polluted water (containing 1,000 ppm of NP) was sequentially subjected to a sonochemical Fenton reaction and biosorption by the filamentous fungus Paecilomyces lilacinus. Although these methods can be used separately, the sequential approach proved more advantageous. In 1 h the sonochemical oxidation, carried out in a 300 kHz US-reactor equipped with a cooling system, halved NP content in polluted water, as determined by GC-MS analysis. The water was then inoculated with pure cultures of the fungus, whose mycelial biomass further reduced NP content in 7 days. Thus an initial NP concentration of 1,000 ppm was reduced approximately by 90%.     

Molybdenum-enriched soybean seeds enhance N accumulation, seed yield, and seed protein content in Brazil

High soybean yields require large amounts of nitrogen (N), which can be obtained mainly from symbiotic N₂ fixation. However, the efficiency of this biological process can be limited by micronutrient deficiencies, especially of molybdenum (Mo). In Brazil, soybean generally responds positively to fertilization with Mo in soils of low fertility and in fertile soils depleted of Mo due to long-term cropping. The micronutrient can be supplied by seed treatment, however toxicity of Mo sources to Bradyrhizobium strains applied to seed as inoculant has been observed, resulting in bacterial death and reductions in nodulation, N₂ fixation and grain yield. Therefore, use of seeds enriched in Mo could be a viable alternative to exterior seed treatment, allowing elite inoculant strains of Bradyrhizobium to sustain high rates of biological N₂ fixation. We demonstrated the feasibility of producing Mo-rich seeds of several soybean cultivars, by means of two foliar sprays of 400 g Mo ha⁻¹ each, between the R3 and R5 stages, with a minimum interval of 10 days between sprays. As a result of this method, considerable increases in seed-Mo content were obtained, of as much as 3000%, in comparison to seeds obtained from plants which received no Mo. In field experiments performed in soils with low N content and without any N-fertilizer supply, inoculation of Mo-rich seeds produced plants with increased N and Mo contents in the grain and higher yields of total N and of grain. In most cases, Mo-rich soybean seeds did not require any further application of Mo-fertilizer.     

Variability of nodulation and dinitrogen fixation capacity among soybean cultivars

 In order to identify soybean cultivars with higher biological N₂ fixation capacities, North American and Brazilian soybean [Glycine max (L.) Merrill] cultivars, belonging to maturity groups VI–VIII, were evaluated for nodulation parameters and N₂ fixation rates. The symbiotic performance of 152 cultivars was evaluated in pots containing 4 kg soil with an established population of the three Bradyrhizobium elkanii strains [29w (SEMIA 5019):SEMIA 566 : SEMIA 587, 22%:36%:34%] which are established in most Brazilian soils cultivated with soybean. Differences were verified among cultivars, with some accumulating up to twice as much nodule dry weight and N in tissues as others. The variability among cultivars was also confirmed when six of them were used in a field experiment, resulting in differences in nodulation, yield and total N accumulated in grains. The analysis of nodule occupancy in 12 cultivars grown either under sterile conditions and receiving a double inoculum and N-free nutrient solution, or in pots containing soil with an established population of bradyrhizobia, showed the preference of cultivars for specific strains. Received: 7 December 1998     

Nitrogen fixation capacity and nodule occupancy by Bradyrhizobium japonicum and B. elkanii strains

 In a previous study soybean Bradyrhizobium strains, used in Brazilian studies and inoculants over the last 30 years, and strains adapted to the Brazilian Cerrados, a region frequently submitted to environmental and nutritional stresses, were analyzed for 32 morphological and physiological parameters in vivo and in vitro. A cluster analysis allowed the subdivision of these strains into species Bradyrhizobium japonicum, Bradyrhizobium elkanii and a mixed genotype. In this study, the bacteria were analyzed for nodulation, N₂ fixation capacity, nodule occupancy and the ability to increase yield. The goal was to find a relationship between the strain groups and the symbiotic performance. Two strains of Brazilian B. japonicum showed higher rates of N₂ fixation and nodule efficiency (mg of N mg^–1 of nodules) under axenic conditions. These strains also showed greater yield increases in field experiments when compared to B. elkanii strains. However, no differences were detected between B. japonicum and B. elkanii strains when comparing nodule occupancy capacity. The adapted strains belonging to the serogroup B. elkanii SEMIA 566, most clustered in a mixed genotype, were more competitive than the parental strain, and some showed a higher capacity of N₂ fixation. Some of the adapted strains, such as S-370 and S-372, have shown similar N₂ fixation rates and nodulation competitiveness to two Brazilian strains of B. japonicum. This similarity demonstrates the possibility of enhancing N₂ fixing ability, after local adaptation, even within B. elkanii species. Differences in the DNA profiles were also detected between the parental SEMIA 566 and the adapted strains by analyses with the ERIC and REP-PCR techniques. Consequently, genetic, morphological and physiological changes can be a result of adaptation of rhizobia to the soil. This variability can be used to select strains capable of increasing the contribution of N₂ fixation to soybean nutrition. Received: 28 May 1997     

Ecophysiology of seedlings of three Mediterranean pine species in contrasting light regimes

Seasonal dynamics of net photosynthesis (Anet) in 2-year-old seedlings of Pinus brutia Ten., Pinus pinea L. and Pinus pinaster Ait. were investigated. Seedlings were grown in the field in two light regimes: sun (ambient light) and shade (25% of photosynthetically active radiation (PAR)). Repeated measures analyses over a 12-month period showed that Anet varied significantly among species and from season to season. Maximum Anet in sun-acclimated seedlings was low in winter (yet remained positive) and peaked during summer. Maximum Anet was observed in June in P. pinea (12 micromol m-2 s-1), July in P. pinaster (23 micromol m-2 s-1) and August in P. brutia (20 micromol m-2 s-1). Photosynthetic light response curves saturated at a PAR of 200-300 micromol m-2 s-1 in winter and in shade-acclimated seedlings in summer. Net photosynthesis in sun-acclimated seedlings did not saturate at PAR up to 1900 micromol m-2 s-1 in P. brutia and P. pinaster. Minimum air temperature of the preceding night was apparently one of the main factors controlling Anet during the day. In shade-acclimated seedlings, photosynthetic rates were reduced by 50% in P. brutia and P. pinaster and by 20% in P. pinea compared with those in sun-acclimated seedlings. Stomatal conductance was generally lower in shaded seedlings than in seedlings grown in the sun, except on days with a high vapor pressure deficit. Total chlorophyll concentration per unit leaf area, specific leaf area (SLA) and height significantly increased in P. pinea in response to shade, but not in P. pinaster or P. brutia. In response to shade, P. brutia showed a significant increase in total chlorophyll concentration but not SLA. Photosynthetic and growth data indicate that P. pinaster and P. brutia are more light-demanding than P. pinea.     

New insights into the origins and evolution of rhizobia that nodulate common bean (Phaseolus vulgaris) in Brazil

It is generally accepted that there are two major centers of genetic diversification of common beans (Phaseolus vulgaris L.): the Mesoamerican (Mexico, Colombia, Ecuador and north of Peru, probably the primary center), and the Andean (southern Peru to north of Argentina) centers. Wild common bean is not found in Brazil, but it has been grown in the country throughout recorded history. Common bean establishes symbiotic associations with a wide range of rhizobial strains and Rhizobium etli is the dominant microsymbiont at both centers of genetic diversification. In contrast, R. tropici, originally recovered from common bean in Colombia, has been found to be the dominant species nodulating field-grown common-bean plants in Brazil. However, a recent study using soil dilutions as inocula has shown surprisingly high counts of R. etli in two Brazilian ecosystems. In the present study, RFLP-PCR analyses of nodABC and nifH genes of 43 of those Brazilian R. etli strains revealed unexpected homogeneity in their banding patterns. The Brazilian R. etli strains were closely similar in 16S rRNA sequences and in nodABC and nifH RFLP-PCR profiles to the Mexican strain CFN 42^T, and were quite distinct from R. etli and R. leguminosarum strains of European origin, supporting the hypothesis that Brazilian common bean and their rhizobia are of Mesoamerican origin, and could have arrived in Brazil in pre-colonial times. R. tropici may have been introduced to Brazilian soils later, or it may be a symbiont of other indigenous legume species and, due to its tolerance to acidic soils and high temperature conditions became the predominant microsymbiont of common bean.     

Inhibition of Key Enzymes Linked to Obesity by Preparations From Mediterranean Dietary Plants: Effects on α-Amylase and Pancreatic Lipase Activities

One of the most important strategy in the treatment of obesity includes the development of nutrient digestion and absorption inhibitors. Inhibition of digestive enzymes is one of the most widely studied mechanisms used to determine the potential efficacy of natural products as hypolipidemic and hypoglycaemic agents. In vitro studies here reported were performed to evaluate the inhibitory activity of five species (as hydroalcoholic extracts) of edible plants from Calabria region (Italy) on amylase and lipase by monitoring the hydrolysis of p-NPC and the hydrolysis of glycoside bonds in digestible carbohydrate foods. The formulation obtained from Clematis vitalba L. exhibited the strongest inhibitory effect on pancreatic lipase (IC₅₀?=?0.99 mg/ml) and on α-amylase (IC₅₀?=?31.52 μg/ml). In order to explore metabolome production HPTLC analysis of the extracts was performed, revealing the predominance of (±)-catechin, caffeic acid and chlorogenic acid in C. vitalba formulation at concentration of 23.18?±?3.14, 13.63?±?0.65 and 18.88?±?0.76 mg/g, respectively. GC/MS analysis was used to identify fatty acids and terpene composition.     

Composition of peptide mixtures derived from simulated gastrointestinal digestion of prolamins from different wheat varieties

Gliadin content of wheat is highly variable, both qualitatively and quantitatively, in function of the plant genetic and of the growing conditions. The gliadins are among the major triggers of celiac disease: peptides derived from the gastrointestinal digestion of these proteins and absorbed from the lamina propria cause the immunological reactions that damage the villous structure in affected subjects. In the present work, the peptide mixtures generated by simulated gastrointestinal digestion of the prolamin fraction extracted from different wheat varieties (Triticum turgidum subsp. durum and Triticum aestivum) were characterized by LC/MS and LC-MS/MS techniques. Peptides related to the amount of α-gliadin, as well as toxic and immunogenic peptides for celiac patients have been identified and quantified using an isotopically labeled internal standard. The quantification demonstrated strong differences among the varieties tested. Some samples, belonging to the same varieties and/or cultivation area, showed a lower α-gliadin content, and a smaller amount of toxic and immunogenic peptides.