Volatilização de amônia do solo após a aplicação de ureia convencional ou com inibidor de urease

Volatilização de NH3 é a principal reação que diminui a eficiência de utilização pelas plantas do N proveniente da ureia, quando ela é aplicada sobre a superfície do solo. A fim de minimizar essa perda, produtos têm sido misturados à ureia para inibir temporariamente a ação da urease. Este trabalho objetivou avaliar alternativas de aplicação de um fertilizante com inibidor de urease, visando a diminuir a volatilização de NH3 relativamente à ureia convencional, em algumas condições ambientais e de solo. Foram desenvolvidos quatro experimentos, todos em condições de laboratório, em 2007 e 2008, em Cambissolo Húmico. Os tratamentos variaram em cada estudo e incluíram combinações de níveis de pH do solo (natural; 5,5; 6,3; e 6,8), umidade do solo (5, 10 ou 20 % de água) e temperaturas ambientais (18 e 35 ºC), além de estados físicos (sólido ou líquido) e de métodos de aplicação dos fertilizantes (na superfície ou incorporado ao solo). As unidades experimentais foram constituídas por bandejas plásticas (23 x 51 x 17 cm) com 12 kg de solo, numa espessura de 15 cm, sobre as quais foram instaladas câmaras coletoras de NH3. A amônia volatilizada foi determinada em várias épocas, nos primeiros 28 dias após a aplicação dos fertilizantes. O pico de volatilização diária de NH3 ocorreu sempre na primeira semana depois da adição dos fertilizantes ao solo, e aconteceu dois a três dias mais tarde para a ureia com inibidor de urease, em relação à ureia convencional. A volatilização de NH3 nem sempre foi maior para a ureia convencional em comparação ao fertilizante contendo inibidor de urease, tampouco para o estado líquido em relação ao granulado. A volatilização de NH3 aumentou com a elevação do pH, da temperatura e da dose aplicada de N e foi menor nos extremos de umidade (solo com 5 % ou com 20 % de água). Para os fertilizantes aplicados sobre a superfície do solo, a taxa máxima de perda diária foi correspondente a 14 kg ha-1 de N, e a perda total acumulada variou de 2 a 50 % do N aplicado, dependendo principalmente do estado físico em que o fertilizante foi aplicado, da umidade do solo e da temperatura ambiente. A incorporação dos fertilizantes amídicos ao solo foi a maneira mais eficaz de minimizar as perdas de N por volatilização.

Effects of nickel and nitrogen soil fertilization on lettuce growth and urease activity

Nickel is a micronutrient involved in nitrogen metabolism and a constituent of the urease molecule. Plant growth and urease activity were evaluated in lettuce (Lactuca sativa L.) grown in soil-filled pots in a 2 x 8 factorial design with two nitrogen (N) sources and eight Ni rates, with five replications. Nitrogen was applied at 200 mg dm-3 (half the dose incorporated into the soil at seedling transplanting and half top-dressed later) using the sources NH4NO3 (AN) and CO(NH2)2 (Ur). The Ni treatments (0, 2, 4, 8, 12, 16, 24 and 32 mg dm-3) were applied as NiCl2. The shoot dry-matter yield, leaf urease activity, Ni levels in the lettuce leaves and Ni levels extracted from soil with Mehlich-3 (M-3) and DTPA were determined. In the plants supplied with AN, the shoot dry-matter yield was higher than in those supplied with Ur. There was no difference in shoot dry matter in response to soil-applied Ni. The leaf urease activity increased with Ni application, regardless of the N source. The extractions with M-3 and DTPA were efficient to evaluate Ni availability for lettuce in the Red-Yellow Latosol.

Synthesis of angiotensin-converting enzyme (ACE) inhibitors: an important class of antihypertensive drugs

This report outlines the discovery, the design and development of new compounds, and, structure-activity relationships for this drug category. Updated approaches to planned syntheses of new worthy ACE-inhibitors are also exploited.

Sistema em fluxo para determinação espectrofotométrica de uréia em plasma de sangue animal empregando leguminosa como fonte natural da enzima urease

A spectrophotometric flow injection analysis (FIA) procedure employing natural urease enzyme source for the determination of urea in animal blood plasma was developed. Among leguminous plants used in the Brazilian agriculture, the Cajanus cajan specie was selected as urease source considering its efficiency and availability. A minicolumn was filled with leguminous fragments and coupled to the FIA manifold, where urea was on-line converted to ammonium ions and subsequently it was quantified by spectrophotometry. The system was employed to determine urea in animal plasma samples without any prior treatment. Accuracy was assessed by comparison results with those obtained employing the official procedure and no significant difference at 90 % confidence level was observed. Other profitable features such as an analytical throughput of 30 determinations per hour, a reagent consumption of 19.2 mg sodium salicylate, 0.5 mg sodium hipochloride and a relative standard deviation of 1.4 % (n= 12) were also obtained.

Structural bioinformatics study of cyclin-dependent kinases complexed with inhibitors

The present work describes molecular models for the binary complexes CDK9, CDK5 and CDK1 complexed with Flavopiridol and Roscovitine. These structural models indicate that the inhibitors strongly bind to the ATP-binding pocket of CDKs and the structural comparison with the complexes CDK2:Flavopiridol and CDK2:Roscovitine correlates the structural differences with differences in inhibition of these CDKs by the inhibitors. These structures open the possibility of testing new inhibitor families, in addition to new substituents for the already known lead structures such as flavones and adenine derivatives.

Inhibitors of Clostridium histolyticum colagenase

Different substances were tested as inhibitors of Clostridium histolyticum collagenase, both experimental and theoretically. The in vitro collagenase activity, alone and in the presence of inhibitors, was quantified by reaction with bovine collagen and dosage of the releasing amino acids. Collagenase-inhibitor interaction was studied theoretically by docking computational calculations. Only one among the tested substances showed inhibitor activity against the bacterial collagenase.

Inhibitors of human collagenase, MMP1

Different common drugs (Meloxicam, Tenoxicam and Piroxicam, and sodium alendronate) were tested both experimental and theoretically as inhibitors of interstitial human collagenase, also known as matrix metalloproteinase 1 (MMP-1). The in vitro collagenase activity, alone and in the presence of inhibitors, was quantified by the reaction with a fluorescent synthetic substrate and measuring the change of emission. Collagenase-inhibitor interaction was studied theoretically by computational calculations. Three among the four tested substances showed moderate inhibiting activity against the human collagenase.

Análise epidemiológica e emprego do teste rápido da urease em pacientes com úlcera péptica perfurada

OBJETIVO: Analisar o perfil epidemiológico de pacientes com úlcera péptica gastroduodenal perfurada e verificar se a presença do H. pylori nas secreções peritoneais e intraluminais desses pacientes pode ser avaliada pelo teste rápido da urease. MÉTODOS: Realizou-se estudo prospectivo, transversal, descritivo, com dados de pacientes atendidos em um hospital de abrangência regional, em portadores de úlcera péptica perfurada. Coletou-se, no transoperatório, amostras de líquido peritoneal (na proximidade da perfuração) e da secreção intraluminal, sendo encaminhadas para cultura e teste rápido de urease. RESULTADOS: Quatorze pacientes foram analisados. A média etária foi 41,06 anos, todos homens, brancos (71,4%), tabagistas (57,2%), IMC < 30 (85,7%), com história prévia de dispepsia (78,6%). Sorologia para H. pylori foi positiva em 84,6% dos casos. O teste rápido da urease foi positivo em 78,6% das amostras do tubo digestivo e em 42,8% das amostras da cavidade peritoneal; 41,6% foram positivos em ambos os locais, 50% somente na cavidade digestiva e 8,4% exclusivamente na cavidade peritoneal. Dos 11 pacientes com sorologia positiva para H. pylori 100% apresentaram positividade em pelo menos um dos sítios pesquisados. CONCLUSÃO: Verificou-se que a incidência foi menor que a esperada. Há associação significativa entre a infecção pelo H. pylori e a ocorrência de perfuração. A presença deste patógeno pode ser avaliada tanto pela sorologia quanto pela realização do teste rápido da urease do fluido coletado na cavidade peritoneal e na luz gástrica/duodenal.

Competitiveness of ALS inhibitors resistant and susceptible biotypes of Greater Beggarticks (Bidens subalternans)

The continuous use of ALS-inhibiting herbicides has led to the evolution of herbicide-resistant weeds worldwide. Greater beggarticks is one of the most troublesome weeds found in the soybean production system in Brazil. Recently, a greater beggarticks biotype that is resistant (R) to ALS inhibitors due to Trp574Leu mutation in the ALS gene was identified. Also, the adaptive traits between susceptible (S) and R to ALS inhibitors biotypes of greater beggarticks were compared. Specifically, we aimed to: (1) evaluate and compare the relative growth rates (RGR) between the biotypes; (2) analyze the seed germination characteristics of R and S biotypes under different temperature conditions; and (3) evaluate their competitive ability in a replacement series study. The experiments were conducted at the University of Arkansas, USA, in 2007 and at Universidade Federal do Rio Grande do Sul (Federal University of Rio Grande do Sul), Brazil, in 2008. Plant proportions for replacement series studies were respectively 100:0, 75:25, 50:50, 25:75 and 0:100, with a total population of 150 plants m-2. There was no difference in RGR between R and S biotypes. The R-biotype germination rate was lower than that of the S biotype. However, at low temperature conditions (15 ºC), the reverse was observed. In general, there is no difference in the competitive ability between R and S greater beggarticks biotypes.

Eletrolite leakage as a technique to diagnose euphorbia heterophylla biotypes resistant to ppo-inhibitors herbicides

The action of herbicides that affect the integrity of cell membranes and cause leakage, like PPO-inhibitors, can be detected by measuring the electric conductivity (EC) of a solution in which the plant tissue target is incubated in the presence of herbicide. The objectives of this work were to confirm PPO resistance in a new Euphorbia heterophylla (EPHHL) biotype, and to compare the electrolyte leakage from R and S to PPO-inhibitors biotypes, using two different methods of incubation in a solution containing herbicides. One experiment was carried in greenhouse and three in laboratory, with a completely randomized design. In the greenhouse experiment, four biotypes of EPHHL were sprayed with seven rates of fomesafen to confirm resistance in suspected biotypes. Leaf disks from R and S EPHHL biotypes in the second and the third experiments and entire leaves in the fourth experiment were incubated in a solution containing PPO-inhibitors to subsequently determine EC of solution. The study confirmed the resistance to PPO-inhibitors in two EPHHL biotypes. There were no significant differences between S and R biotypes in the experiments with the incubation of leaf disks, but incubation of entire leaves of EPHHL S biotype showed higher EC when in a solution with fomesafen, in comparison to the R biotype. The results of this work are an indirect evidence that resistance to PPO-inhibitors is related to lower absorption of herbicide by the shoots and also to some kind of mechanism to cope with oxidative stress.

Resistance to ACCase inhibitors in Eleusine indica from Brazil involves a target site mutation

Eleusine indica (goosegrass) is a diploid grass weed which has developed resistance to ACCase inhibitors during the last ten years due to the intensive and frequent use of sethoxydim to control grass weeds in soybean crops in Brazil. Plant dose-response assays confirmed the resistant behaviour of one biotype obtaining high resistance factor values: 143 (fenoxaprop), 126 (haloxyfop), 84 (sethoxydim) to 58 (fluazifop). ACCase in vitro assays indicated a target site resistance as the main cause of reduced susceptibility to ACCase inhibitors. PCR-generated fragments of the ACCase CT domain of the resistant and sensitive reference biotype were sequenced and compared. A point mutation was detected within the triplet of aspartate at the amino acid position 2078 (referred to EMBL accession no. AJ310767) and resulted in the triplet of glycine. These results constitute the first report on a target site mutation for a Brazilian herbicide resistant grass weed.

Growth inhibitors in turfgrass

Well-maintained lawns are comfortable and safe places for leisure activities and sports practice, and they also bring environmental benefits; for example, they reduce soil exposure to erosion and releases atmospheric CO2, thus reducing the greenhouse effect. However, regardless of the purpose of use or the choice of the plant species to form the lawn, the highest costs involve cutting that is needed to keep the turfgrass at its appropriate height. Successive lawn cutting operations are necessary basically because of the vegetative and reproductive growth of turfgrass which, in Brazil, occurs mainly from October to March. Expenditures with successive mechanical cuttings have fostered the search of alternative procedures to keep lawn plants at appropriate height, such as the use of plant growth inhibitors, an increasingly interesting procedure. Since the use of this technology in Brazil is still at its early stage, the aim of this literature review is to examine aspects associated with lawn management by using growth inhibitors. Another alternative is to increase the knowledge of the classification and rational application of the different compounds currently available in the market.

DNA topoisomerase inhibitors: biflavonoids from Ouratea species

Topoisomerase inhibitors are agents with anticancer activity. 7"-O-Methyl-agathisflavone (I) and amentoflavone (II) are biflavonoids and were isolated from the Brazilian plants Ouratea hexasperma and O. semiserrata, respectively. These biflavonoids and the acetyl derivative of II (IIa) are inhibitors of human DNA topoisomerases I at 200 µM, as demonstrated by the relaxation assay of supercoiled DNA, and only agathisflavone (I) at 200 µM also inhibited DNA topoisomerases II-alpha, as observed by decatenation and relaxation assays. The biflavonoids showed concentration-dependent growth inhibitory activities on Ehrlich carcinoma cells in 45-h culture, assayed by a tetrazolium method, with IC50 = 24 ± 1.4 µM for I, 26 ± 1.1 µM for II and 10 ± 0.7 µM for IIa. These biflavonoids were assayed against human K562 leukemia cells in 45-h culture, but only I showed 42% growth inhibitory activity at 90 µM. Our results suggest that biflavonoids are targets for DNA topoisomerases and their cytotoxicity is dependent on tumor cell type.

Glycosaminoglycans affect the interaction of human plasma kallikrein with plasminogen, factor XII and inhibitors

Human plasma kallikrein, a serine proteinase, plays a key role in intrinsic blood clotting, in the kallikrein-kinin system, and in fibrinolysis. The proteolytic enzymes involved in these processes are usually controlled by specific inhibitors and may be influenced by several factors including glycosaminoglycans, as recently demonstrated by our group. The aim of the present study was to investigate the effect of glycosaminoglycans (30 to 250 µg/ml) on kallikrein activity on plasminogen and factor XII and on the inhibition of kallikrein by the plasma proteins C1-inhibitor and antithrombin. Almost all available glycosaminoglycans (heparin, heparan sulfate, bovine and tuna dermatan sulfate, chondroitin 4- and 6-sulfates) reduced (1.2 to 3.0 times) the catalytic efficiency of kallikrein (in a nanomolar range) on the hydrolysis of plasminogen (0.3 to 1.8 µM) and increased (1.9 to 7.7 times) the enzyme efficiency in factor XII (0.1 to 10 µM) activation. On the other hand, heparin, heparan sulfate, and bovine and tuna dermatan sulfate improved (1.2 to 3.4 times) kallikrein inhibition by antithrombin (1.4 µM), while chondroitin 4- and 6-sulfates reduced it (1.3 times). Heparin and heparan sulfate increased (1.4 times) the enzyme inhibition by the C1-inhibitor (150 nM).

Interruption of the blood-stage cycle of the malaria parasite, Plasmodium chabaudi, by protein tyrosine kinase inhibitors

Malaria is a devastating disease caused by a unicellular protozoan, Plasmodium, which affects 3.7 million people every year. Resistance of the parasite to classical treatments such as chloroquine requires the development of new drugs. To gain insight into the mechanisms that control Plasmodium cell cycle, we have examined the effects of kinase inhibitors on the blood-stage cycle of the rodent malaria parasite, Plasmodium chabaudi. In vitro incubation of red blood cells for 17 h at 37ºC with the inhibitors led to a decrease in the percent of infected cells, compared to control treatment, as follows: genistein (200 µM - 75%), staurosporine (1 µM - 58%), R03 (1 µM - 75%), and tyrphostins B44 (100 µM - 66%) and B46 (100 µM - 68%). All these treatments were shown to retard or prevent maturation of the intraerythrocytic parasites. The diverse concentration ranges at which these inhibitors exert their effects give a clue as to the types of signals that initiate the transitions between the different developmental stages of the parasite. The present data support our hypothesis that the maturation of the intraerythrocytic cycle of malaria parasites requires phosphorylation. In this respect, we have recently reported a high Ca2+ microenvironment surrounding the parasite within red blood cells. Several kinase activities are modulated by Ca2+. The molecular identification of the targets of these kinases could provide new strategies against malaria.