The influence of water level on macrophyte growth and trophic interactions in eutrophic Mediterranean shallow lakes: a mesocosm experiment with and without fish

1. Water‐level fluctuations are typical of lakes located in the semi‐arid Mediterranean region, which is characterised by warm rainy winters and hot dry summers. Ongoing climate change may exacerbate fluctuations and lead to more severe episodes of drought, so information on the effects of water level on the functioning of lake ecosystems in such regions is crucial. 2. In eutrophic Lake Eymir, Turkey, we conducted a 4‐month (summer) field experiment using cylindrical 0.8‐m‐ (low‐water‐level) and 1.6‐m‐deep (high‐water‐level) mesocosms (kept open to the sediment and atmosphere). Fish (tench, Tinca tinca, and bleak, Alburnus escherichii) were added to half of the mesocosms, while the rest were kept fishless. Ten shoots of Potamogeton pectinatus were transplanted to each mesocosm. 3. Sampling for physicochemical variables, chlorophyll a (chl‐a), zooplankton and per cent plant volume inhabited (PVI%) by macrophytes was conducted weekly during the first 5 weeks, and subsequently biweekly. Macrophytes were harvested on the last sampling date. During the course of the experiment, the water level decreased by 0.41 ± 0.06 m. 4. Throughout the experiment, fish affected zooplankton abundance (?), nutrient concentrations (+), chl‐a (+) and water clarity (?) most strongly in the low‐water‐level mesocosms and the zooplankton community shifted towards dominance of small‐sized forms. The fishless mesocosms had a higher zooplankton/phytoplankton ratio, suggesting higher grazing. 5. Greatest macrophyte growth was observed in the low‐water‐level fishless mesocosms. However, despite high nutrient concentrations and low water clarity, macrophytes were also abundant in the fish mesocosms and particularly increased following a water‐level decrease from midsummer onwards. Macrophyte growth was poor in the high‐water‐level mesocosms, even in the fishless ones with high water clarity. This was ascribed to extensive periphyton development reducing light availability for the macrophytes. 6. Our results indicate that a reduction in water level during summer may help maintain the growth of macrophytes in Mediterranean eutrophic shallow lakes, despite a strong negative effect of fish predation on water clarity. It is therefore probable that an expected negative effect of global climate change on water clarity because of eutrophication and enhanced top‐down control of fish may be, at least partly, counteracted by reduced water level, provided that physical disturbance is not severe.     

Studies of Nitric Oxide Production in Rat Tissues in Postnatal Development by Electron Paramagnetic Resonance Spectroscopy

Biophysics - Paramagnetic complexes containing nitric oxide (NO) have been assayed in rat heart and liver tissues by EPR spectroscopy to investigate the time variation of NO production during...     

Discovery of novel anti-HIV-1 agents based on a broadly neutralizing antibody against the envelope gp120 V3 loop: a computational study

A computer-aided search for novel anti-HIV-1 agents able to mimic the pharmacophore properties of broadly neutralizing antibody (bNAb) 3074 was carried out based on the analysis of X-ray complexes of this antibody Fab with the MN, UR29, and VI191 peptides from the V3 loop of the HIV envelope protein gp120. Using these empirical data, peptidomimetic candidates of bNAb 3074 were identified by a public, web-oriented virtual screening platform (pepMMsMIMIC) and models of these candidates bound to the above V3 peptides were generated by molecular docking. The docking calculations identified four molecules exhibiting a high affinity to all of the V3 peptides. These molecules were selected as the most probable peptidomimetics of bNAb 3074. Finally, the stability of the complexes of these molecules with the MN, UR29, and VI191 V3 peptides was estimated by molecular dynamics and free energy simulations. Specific binding to the V3 loop was accomplished primarily by π–π interactions between the aromatic rings of the peptidomimetics and the conserved Phe-20 and/or Tyr-21 of the V3 immunogenic crown. In a mechanism similar to that of bNAb 3074, these compounds were found to block the tip of the V3 loop forming its invariant structural motif that contains residues critical for cell tropism. Based on these findings, the compounds selected are considered as promising basic structures for the rational design of novel, potent, and broad-spectrum anti-HIV-1 therapeutics.     

Variability of continuous insect cell lines and their identification

Continuous insect cell lines make a special object of research in biology. Insect cells in the established lines differ in the number of attributes from both normal differentiated, and embryonic cells. The period of genome destabilization necessarily precedes cell line immortalization. Genome destabilization is manifested by changes in genome size, cell karyotype, amplification of some retrotransposone families, and induction of their expression. The existence of significant genetic variability in one line puts a problem of searching for invariant attributes providing culture identification and defining the limits of normal polymorphism of cells in the culture. Using the vast collection of insect continuous cell lines stored at the N. I. Vavilov Institute of General Genetics RAS, nine lines were identified by RFLP method of mitochondrial DNA. Variability of DNA-polymorphisms, cellular karyology, morphology, immunological and biochemical attribute in the culture is discussed.     

Method of determining protein conformations by the two-dimensional nuclear Overhauser enhancement spectroscopy data

A method is suggested to determine the most probable values of the angles phi, psi of the protein backbone by the data on the availability and absence of d connectivities in the two-dimensional nuclear Overhauser enhancement spectra. In view of this, the dependences of the proton-proton distances in dipeptide units of L-amino acid residues on the dihedral angles phi, psi, chi1 are considered and the conformational states of amino acid residues of the proteins with the known spatial structure are analysed statistically. The potentialities of the method are assessed with the aid of model spectral nuclear magnetic resonance (NMR) parameters obtained from the X-ray data for the bovine pancreatic trypsin inhibitor and avian pancreatic polypeptide. It is shown that the developed procedure of structural interpretation of the NMR data allows one to correctly reproduce the local conformation of the protein backbone. The obtained backbone conformation may serve as a starting point to build and refine molecular three-dimensional structure.     

Effect of Anionic Salt and Highly Fermentable Carbohydrate Supplementations on Urine pH and on Experimentally Induced Hypocalcaemia in Cows

The objective of this experiment was to determine the effect of dietary grain on calcium homeostasis. Six rumen-fistulated dairy cows with 3 or more previous lactations and no history of parturient paresis were randomly assigned to a sequence of diets in a crossover study with 4 periods of 10 days each. Dietary treatments were: A control ration consisting of wrap grass silage alone (1), the control ration supplemented with ammonium chloride and ammonium sulphate salt solution (2), control ration following a period with supplementation (3) and control ration supplemented with increasing amounts of barley from 4 to 10 kg/cow per day, expected to produce subclinical rumen acidosis (4). Daily intake of the diets was adjusted to 14 kg DM/cow per day. On day 11, the calcium-regulating mechanisms in cows were challenged until recumbency by a standardized intravenous EDTA infusion and cows were left to recover spontaneously. Anion supplementation and the feeding of highly fermentable carbohydrate lowered urine pH below 7.0 due to subclinical acidosis. During spontaneous recovery from EDTA induced hypocalcaemia, the cows more quickly regained a whole blood free calcium concentration of 1.00 mmol/L if they had most recently been supplemented with either anionic salts or with increasing amounts of barley, as compared to the basic ration. It is concluded that so-called slug-feeding or 'steaming up' with highly fermentable carbohydrates before parturition in milk fever susceptible cows enhanced calcium homeostasis similar to the effect seen in cows on anionic diets.     

Synthesis and Properties of Some Morpholino Oligonucleotide Analogues

Abstract

The solid phase synthesis of the three types of morpholino analogues of nucleic acids has been accomplished and their hybridization properties were evaluated.     

Nifedipine loaded chitosan microspheres prepared by emulsification phase-separation

A high yield of nifedipine-chitosan microspheres could be obtained using an emulsification phase-separation method. A high level of entrapment of nifedipine in the microspheres was achieved. The microspheres exhibited excellent swelling properties. Differential scanning calorimetry, X-ray diffractometry, and scanning electron microscopy confirmed that at 1.84% loading, nifedipine was dispersed molecularly. The microspheres exhibited faster release at low loadings compared to high loadings. Fitting the data to the coupled Fickian/case II equation, showed that at low loadings polymer relaxation coefficients (k₂) were high. As the polymer content increased in the microspheres, the value of n (diffusional exponent characteristic of the release mechanism) approached one, which is indicative of zero order.