Conservation agriculture, increased organic carbon in the top-soil macro-aggregates and reduced soil CO2 emissions

Background and aims

Conservation agriculture, the combination of minimal soil movement (zero or reduced tillage), crop residue retention and crop rotation, might have the potential to increase soil organic C content and reduce emissions of CO₂.

Methods

Three management factors were analyzed: (1) tillage (zero tillage (ZT) or conventional tillage (CT)), (2) crop rotation (wheat monoculture (W), maize monoculture (M) and maize-wheat rotation (R)), and (3) residue management (with (+r), or without (?r) crop residues). Samples were taken from the 0–5 and 5–10?cm soil layers and separated in micro-aggregates (< 0.25?mm), small macro-aggregates (0.25 to 1?mm) and large macro-aggregates (1 to 8?mm). The carbon content of each aggregate fraction was determined.

Results

Zero tillage combined with crop rotation and crop residues retention resulted in a higher proportion of macro-aggregates. In the 0–5?cm layer, plots with a crop rotation and monoculture of maize and wheat in ZT+r had the greatest proportion of large stable macro-aggregates (40%) and highest mean weighted diameter (MWD) (1.7?mm). The plots with CT had the largest proportion of micro-aggregates (27%). In the 5–10?cm layer, plots with residue retention in both CT and ZT (maize 1?mm and wheat 1.5?mm) or with monoculture of wheat in plots under ZT without residues (1.4?mm) had the greatest MWD. The 0–10?cm soil layer had a greater proportion of small macroaggregates compared to large macro-aggregates and micro-aggregates. In the 0–10?cm layer of soil with residues retention and maize or wheat, the greatest C content was found in the small and large macro-aggregates. The small macro-aggregates contributed most C to the organic C of the sample. For soil cultivated with maize, the CT treatments had significantly higher CO₂ emissions than the ZT treatments. For soil cultivated with wheat, CTR-r had significantly higher CO₂ emissions than all other treatments.

Conclusion

Reduction in soil disturbance combined with residue retention increased the C retained in the small and large macro-aggregates of the top soil due to greater aggregate stability and reduced the emissions of CO₂ compared with conventional tillage without residues retention and maize monoculture (a cultivation system normally used in the central highlands of Mexico).     

Hypothyroidism modifies lipid composition of polymorphonuclear leukocytes

Thyroid hormones are important regulators of lipid metabolism. Polymorphonuclear leukocytes (PMN) are essential components of innate immune response. Our goal was to determine whether hypothyroidism affects lipid metabolism in PMN cells. Wistar rats were made hypothyroid by administrating 0.1 g/L 6-propyl-2-thiouracil (PTU) in drinking water during 30 days. Triacylglycerides (TG), cholesterol and phospholipids were determined in PMN and serum by conventional methods. The mRNA expression of LDL receptor (LDL-R), 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCoAR), sterol regulatory element binding protein 2 (SREBP-2), and diacylglycerol acyltransferase 2 (DGAT-2) were quantified by Real-Time PCR. Cellular neutral lipids were identified by Nile red staining. We found hypothyroidism decreases serum TG whereas it increases them in PMN. This result agrees with those observed in Nile red preparations, however DAGT-2 expression was not modified. Cholesterol synthesizing enzyme HMGCoAR mRNA and protein was reduced in PMN of hypothyroid rats. As expected, cholesterol content decreased in the cells although it increased in serum. Hypothyroidism also reduced relative contents of palmitic, stearic, and arachidonic acids, whereas increased the myristic, linoleic acids, and the unsaturation index in PMN. Thus, hypothyroidism modifies PMN lipid composition. These findings would emphasize the importance of new research to elucidate lipid-induced alterations in specific function(s) of PMN.     

A spontaneous genomic deletion in Listeria ivanovii identifies LIPI-2, a species-specific pathogenicity island encoding sphingomyelinase and numerous internalins

Listeria ivanovii differs from the human pathogen Listeria monocytogenes in that it specifically affects ruminants, causing septicaemia and abortion but not meningo-encephalitis. The genetic characterization of spontaneous L. ivanovii mutants lacking the virulence factor SmcL (sphingomyelinase) led us to identify LIPI-2, the first species-specific pathogenicity island from Listeria. Besides SmcL, this 22 kb chromosomal locus encodes 10 internalin (Inl) proteins: i-InlB1 and -B2 are large/surface-associated Inls similar to L. monocytogenes InlB; i-InlE to -L are small/excreted (SE)-Inls, i-InlG being a tandem fusion of two SE-Inls. Except i-inlB1, all LIPI-2 inl genes are controlled by the virulence regulator, PrfA. LIPI-2 is inserted into a tRNA locus and is unstable - half of it deleting at approximately 10(-4) frequency with a portion of contiguous DNA. The spontaneous mutants were attenuated in vivo in mice and lambs and showed impaired intracellular growth and apoptosis induction in bovine MDBK cells. Targeted knock-out mutations associated the virulence defect with LIPI-2 genes. The region between the core genome loci ysnB-tRNA(arg) and ydeI flanking LIPI-2 contained different gene complements in the different Listeria spp. and even serovars of L. monocytogenes, including remnants of the PSA bacteriophage int gene in serovar 4b, indicating it is a hot spot for horizontal genome diversification. LIPI-2 is conserved in L. ivanovii ssp. ivanovii and londoniensis, suggesting an early acquisition during the species' evolution. LIPI-2 is likely to play an important role in the pathogenic and host tropism of L. ivanovii.     

A New Conformation in Sarcoplasmic Reticulum Calcium Pump and Plasma Membrane Ca2+ Pumps Revealed by a Photoactivatable Phospholipidic Probe

The purpose of this work was to obtain structural information about conformational changes in the membrane region of the sarcoplasmic reticulum (SERCA) and plasma membrane (PMCA) Ca²⁺ pumps. We have assessed changes in the overall exposure of these proteins to surrounding lipids by quantifying the extent of protein labeling by a photoactivatable phosphatidylcholine analog 1-palmitoyl-2-[9-[2′-[¹²⁵I]iodo-4′-(trifluoromethyldiazirinyl)-benzyloxycarbonyl]-nonaoyl]-sn-glycero-3-phosphocholine ([¹²⁵I]TID-PC/16) under different conditions. We determined the following. 1) Incorporation of [¹²⁵I]TID-PC/16 to SERCA decreases 25% when labeling is performed in the presence of Ca²⁺. This decrease in labeling matches qualitatively the decrease in transmembrane surface exposed to the solvent calculated from crystallographic data for SERCA structures. 2) Labeling of PMCA incubated with Ca²⁺ and calmodulin decreases by approximately the same amount. However, incubation with Ca²⁺ alone increases labeling by more than 50%. Addition of C28, a peptide that prevents activation of PMCA by calmodulin, yields similar results. C28 has also been shown to inhibit ATPase SERCA activity. Interestingly, incubation of SERCA with C28 also increases [¹²⁵I]TID-PC/16 incorporation to the protein. These results suggest that in both proteins there are two different E₁ conformations as follows: one that is auto-inhibited and is in contact with a higher amount of lipids (Ca²⁺ + C28 for SERCA and Ca²⁺ alone for PMCA), and one in which the enzyme is fully active (Ca²⁺ for SERCA and Ca²⁺-calmodulin for PMCA) and that exhibits a more compact transmembrane arrangement. These results are the first evidence that there is an autoinhibited conformation in these P-type ATPases, which involves both the cytoplasmic regions and the transmembrane segments.Although membrane proteins constitute more than 20% of the total proteins, the structure of only few of them is known in detail. An important group of integral membrane proteins are ion-motive ATPases. These proteins belong to the family of P-type ATPases, which share in common the formation of an acid-stable phosphorylated intermediate as part of its reaction cycle. Crystallographic information is available for a few members of this family. There are several crystal structures of the Ca²⁺ pump of sarcoplasmic reticulum (SERCA)² revealing different conformations (1–5), and recently, crystal structures of the H⁺-ATPase (6) and of the Na,K-ATPase were reported as well (7).We are interested in obtaining structural information about the plasma membrane calcium pump (PMCA). This pump is an integral part of the Ca²⁺ signaling mechanism (8). It is highly regulated by calmodulin, which activates this protein by binding to an auto-inhibitory region and changing the conformation of the pump from an inhibited state to an activated one (8, 9). Crystallization of PMCA is particularly challenging because there is no natural source from which this protein can be obtained in large quantities. Moreover, the presence of several isoforms in the same tissue further complicates efforts to obtain a homogeneous sample suitable for crystallization.Information about the structure and assembly of the transmembrane domain of an integral membrane protein can also be obtained from the analysis of the lipid-protein interactions. In this work, we have used a hydrophobic photolabeling method to study the noncovalent interactions between PMCA and the surrounding phospholipids under different experimental conditions that lead to known conformations. We employed the photoactivatable phosphatidylcholine analog 1-palmitoyl-2-[9-[2′-[¹²⁵I]iodo-4′-(trifluoromethyldiazirinyl)-benzyloxycarbonyl]-nonaoyl]-sn-glycero-3-phosphocholine ([¹²⁵I]TID-PC/16) that has been previously used to analyze lipid-protein interfaces (10–12). This reagent is located in the phospholipidic milieu, and upon photolysis it reacts indiscriminately with its molecular neighbors. It is thus possible to directly analyze the interaction between a membrane protein and lipids belonging to its immediate environment (13–15). By measuring the amount of labeling of SERCA in conditions that promote conformations for which there are well resolved crystal structures, we were able to validate this photolabeling approach as a convenient tool for analyzing conformational changes within transmembrane regions. Furthermore, using this technique on PMCA and comparing the results obtained for SERCA, we were able to draw structural conclusions about these proteins under activated and inhibited states.     

Mycobiota and mycotoxins in fermented feed,wheat grains and corn grains in Southeastern Buenos Aires Province,Argentina

Wheat (as bran) and corn (as dry grain or fermented feed) are main ingredients of feedstuffs used in local cattle and pig farms in the South of the Buenos Aires Province (Argentina). Therefore, determining mycobiota and mycotoxins in wheat and corn is of prime importance for developing feed management techniques to optimise animal production and to minimize toxicity. Then, a mycological survey was carried out in the Southeastern part of the Buenos Aires Province, in order to identify the mycobiota and the main mycotoxins present in fermented feed, wheat grain and corn grain samples. Samples were cultured for fungal quantification, isolation and identification, and analysed for deoxynivalenol (DON), zearalenone (ZEA), T-2 toxin and aflatoxins (AFLA). Penicillium (74%), Aspergillus (32%) and Scopulariopsis (21%) were the prevalent genera in fermented feed. Penicillium (70%), Fusarium (47%) and Aspergillus (34%) were the most frequent fungi isolated from corn. Penicillium (42%), Fusarium (27%) and Alternaria (25%) were the most frequently recovered genera from wheat. DON was detected in 59% of the corn samples, in 45% of the wheat samples and in 38% of the silage samples. ZEA was detected in 36% of the corn samples, in 49% of the wheat samples and in 16% of the silage samples. T-2 toxin and aflatoxin B1 were each detected in 4% of the corn samples. Eighteen percent of the fermented feed samples showed T-2 contamination. Fermented feed and wheat samples were negative for AFLA.     

Screening of plant peptidases for the synthesis of arginine-based surfactants

Partially purified preparations with proteolytic activity, obtained from South American native plants, were used as biocatalysts in condensation reactions of N-protected arginine alkyl ester derivatives with decylamine and dodecylamine in low-water content systems. The final products are cationic surfactants with potential application as emulsifiers and preservatives. Most of the proteolytic extracts were obtained from latex of species belonging to the Asclepiadaceae family (araujiain from Araujia hortorum, asclepain c from Asclepias curassavica and funastrain from Funastrum clausum). Hieronymain was obtained from unripe fruits of Bromelia hieronymi (Bromeliaceae). Plant proteases from commercial sources (papain and bromelain) were also tested as catalysts in the same reactions. Araujiain and funastrain furnished good reaction conversions (60–84%, with a ratio synthesis/hydrolysis of 2–5) similar to those obtained with commercial papain. Moreover, araujiain was the biocatalyst which rendered the best conversions (60%) for the synthesis of the two novel Bz-Arg-NH-dodecylamide (Bz-Arg-NHC₁₂) and Bz-Arg-NH-decylamide (Bz-Arg-NHC₁₀) derivatives. Moderate to poor conversions (10–50%, showing a ratio synthesis/hydrolysis of 0.5–1) were achieved with asclepain c, hieronymain and bromelain. The screening presented in this work revealed that, although these are structurally similar, their behavior for the synthesis of this kind of products differ among them.     

Trypanosoma cruzi: Biological characterization of a isolate from an endemic area and its susceptibility to conventional drugs

We describe some biological and molecular characteristics of a Trypanosoma cruzi isolate derived from a Triatomine captured in Nicaragua. PCR based typification showed that this isolate, named Nicaragua, belonged to the lineage Tc I. Nicaragua infected culture cells were treated with allopurinol, showing different behavior according to the cellular compartment, being cardiomyocyte primary cultures more resistant to this drug. The course of the infection in a mice experimental model and its susceptibility to benznidazole and allopurinol was analyzed. In benznidazole treatment, mice reverted the high lethal effect of parasites during the acute infection, however, a few parasites were detected in the heart of 88% of mice 1 year post-infection. Since T. cruzi is a heterogeneous species population it is important to study and characterize different parasites actually circulating in humans in endemic areas. In this work we show that T. cruzi Nicaragua isolate, is sensitive to early benznidazole treatment.     

The Intra-Hippocampal Leucine Administration Impairs Memory Consolidation and LTP Generation in Rats

Leucine accumulates in fluids and tissues of patients affected by maple syrup urine disease, an inherited metabolic disorder, predominantly characterized by neurological dysfunction. Although, a variable degree of cognition/psychomotor delay/mental retardation is found in a considerable number of individuals affected by this deficieny, the mechanisms underlying the neuropathology of these alterations are still not defined. Therefore, the aim of this study was to investigate the effect of acute intra-hippocampal leucine administration in the step-down test in rats. In addition, the leucine effects on the electrophysiological parameter, long-term potentiation generation, and on the activities of the respiratory chain were also investigated. Male Wistar rats were bilaterally administrated with leucine (80 nmol/hippocampus; 160 nmol/rat) or artificial cerebrospinal fluid (controls) into the hippocampus immediately post-training in the behavioral task. Twenty-four hours after training in the step-down test, the latency time was evaluated and afterwards animals were sacrificed for assessing the ex vivo biochemical measurements. Leucine-treated animals showed impairment in memory consolidation and a complete inhibition of long-term potentiation generation at supramaximal stimulation. In addition, a significant increment in complex IV activity was observed in hippocampus from leucine-administered rats. These data strongly indicate that leucine compromise memory consolidation, and that impairment of long-term potentiation generation and unbalance of the respiratory chain may be plausible mechanisms underlying the deleterious leucine effect on cognition.