The effect of light levels on daily patterns of chlorophyll fluorescence and organic acid accumulation in the tropical CAM treeClusia hilariana

Sandy plains are characteristic of the coastal region of Brazil. We investigated the diel patterns of changes in organic acid levels, leaf conductance and chlorophylla fluorescence for sun-exposed and shaded plants ofClusia hilariana, one of the dominant woody species in the sandy coastal plains of northern Rio de Janeiro state. Both exposed and shaded plants showed a typical CAM pattern with considerable diel oscillations in organic acid levels. The degradation of both malic and citric acids during the midday stomatal closure period could lead to potential CO₂ fixation rates of 28 mol m^-2 s^-1 in exposed leaves. Moreover, exposed leaves exhibited large increases in total non-photochemical quenching (q_N) accompanied by a substantial decrease in effective quantum yield during the course of the day. However, these potential high rates of CO₂ fixation and the increases inqn of exposed plants were not enough to maintain the primary electron acceptor of photosystem II (q_A) in a low reduction state, similar to that of shaded plants. As a result, there was a moderate increase in the reduction state of q_A throughout the day. Most of the decline in photochemical efficiency of exposed leaves ofC. hilariana was reversible, as evidenced by the high levels of pre-dawn potential quantum yields (F_v/F_m) and their rapid recovery after sunset. However, the depletion of the organic acid pool in the afternoon resulted in an accentuated subsequent drop in F_v/F_m, suggesting that prolonged periods of water stress accompanied by high irradiance levels may expose plants ofC. hilariana in unprotected habitats to the danger of photoinhibition.     

Cyclodextrins enhance the aerobic degradation and dechlorination of low-chlorinated biphenyls

Summary The aerobic dechlorination of 4-chlorobiphenyl and of Aroclor 1221 by Pseudomonas sp. CPE1 strain was enhanced by the presence of hydroxypropyl--cyclodextrin in the medium. The best dechlorination results were obtained when 4-chlorobiphenyl or Aroclor 1221 and the cyclodextrin were used at the molar ratios 1:1 and 1:1.5. This agent can be adopted to enhance the efficiency of PCB degradation tests.     

Synthesis and biological evaluation of novel NK-1 tachykinin receptor antagonists: The use of cycloalkyl amino acids as a template

In the course of a program aimed at synthesizing novel, potent NK-1 tachykinin receptor antagonists, we developed upon a bioactive model by comparing the low energy structures of a series of peptide and nonpeptide Substance P antagonists. The comparison was based on the super imposition of the aromatic rings, assuming that the rest of the molecule behaves predominantly as a template to arrange the key aromatic groups in the right spatial position. A series of 2-aminocyclohexane carboxylic acid analogues were then selected as the best templates for reproducing the postulated bioactive structure, leading to several pseudo-peptides with interesting biological activity. According to the molecular modeling, these compounds exhibit a neat parallel facing of the indolyl and naphthyl groups at about 3 Å distance. Ultraviolet absorption and steady state fluorescence measurements support this conclusion, showing a linear correlation between the spectral properties and the binding affinity of these analogues. Stacking of the indole ring with naphthalene gives rise to a complex characterized by a well-defined molar extinction coefficient. Consistently, steady state and lifetime fluorescence measurements suggest that the quenching process is ascribable to ground-state interactions between the chromophores. Implications of the π stacking propensity of aromatic groups in the biological activity of the compounds examined are briefly discussed. © 1995 John Wiley & Sons, Inc.     

Expression of {beta}-galactoside {alpha}2,6-sialyltransferase does not alter the susceptibility of human colon cancer cells to NK-mediated cell lysis

The extent of processing of N-linked oligosaccharides and thesialylation of the target cell membranes has been positivelycorrelated with resistance to lysis mediated by NK cells, buta conclusive evidence has never been reached. Colon cancer tissuesexpress an increased activity of ß-ga-lactoside     

Production of IL-10 by CD4+ T lymphocytes correlates with down-regulation of Th1 cytokine synthesis in helminth infection.

After the onset of parasite egg deposition, mice infected with the helminth Schistosoma mansoni mount strong Th2 cytokine responses in the absence of significant Th1 cytokine synthesis. To examine the basis of this immunoregulatory state, spleen or lymph node cells from schistosome-infected mice were stimulated with parasite-specific Ag and the supernatants tested for their capacity to suppress IFN-gamma synthesis by a Th1 cell line. Strong inhibition was observed that was neutralized by a mAb against IL-10, a cytokine previously shown to down-regulate Th1 cytokine synthesis. By means of ELISA measurements the production of IL-10 in schistosome infection was confirmed and shown to depend on CD4+ T cells. IL-10 synthesis stimulated by either mitogen or Ag was observed only at those stages of infection when Th2 response induction and Th1 cytokine down-regulation also occurred and was not detected in mice vaccinated with attenuated parasites. Moreover, the addition of the neutralizing anti-IL-10 mAb to Ag-stimulated spleen cell cultures from infected mice caused a dramatic augmentation in IFN-gamma synthesis. These findings suggest that IL-10 is responsible for the down-regulation of Th1 responses observed in schistosome infections, a phenomenon that may enable the parasite to escape potentially harmful cell-mediated responses.     

Structural investigation of the capsular polysaccharide of klebsiella serotype K26

The structure of the capsular polysaccharide from Klebsiella K26 has been determined by using the techniques of methylation, periodate oxidation, partial hydrolysis, and β-elimination. N.m.r. spectroscopy (¹H and ¹³C) was used to establish the nature of the anomeric linkages and to identify oligosaccharides obtained by the different degradative techniques employed.The polysaccharide is comprised of repeating units of the heptasaccharide shown.

     

Common and rare species respond to similar niche processes in macroinvertebrate metacommunities

Ecologists have long investigated why communities are composed of a few common species and many rare species. Most studies relate rarity to either niche differentiation among species or spatial processes. There is a parallel between these processes and the processes proposed to explain the structure of metacommunities. Based on a metacommunity perspective and on data on stream macroinvertebrates from different regions of Brazil, we answer two questions. 1) Are sets of common and rare species affected by similar niche and spatial processes? 2) How does the community composition of common and of rare species differ? The main hypothesis we test is that common species are mainly affected by environmental factors, whereas rare species are mostly influenced by dispersal limitation. We used variation partitioning to determine the proportion of variation explained by the environment and space in common and rare species matrices. Contrary to our expectations, evidence supported the idea that both common and rare species are affected mainly by environmental factors, even after controlling for the differing information content between common and rare species matrices. Moreover, the abundance of some common species is also a good predictor of variation in rare species matrices. Niche differences are unlikely to be the sole cause of patterns of rarity in these metacommunities. We suggest that sets of common and rare species react to similar major environmental gradients and that rare species also respond to processes that operate at a more fine‐grained spatial scale, particularly biotic interactions. We extend the view that species sorting is the dominant process structuring metacommunities and argue that future studies focusing on rarity would benefit from a metacommunity perspective.     

Lysosomal fusion and SNARE function are impaired by cholesterol accumulation in lysosomal storage disorders

The function of lysosomes relies on the ability of the lysosomal membrane to fuse with several target membranes in the cell. It is known that in lysosomal storage disorders (LSDs), lysosomal accumulation of several types of substrates is associated with lysosomal dysfunction and impairment of endocytic membrane traffic. By analysing cells from two severe neurodegenerative LSDs, we observed that cholesterol abnormally accumulates in the endolysosomal membrane of LSD cells, thereby reducing the ability of lysosomes to efficiently fuse with endocytic and autophagic vesicles. Furthermore, we discovered that soluble N‐ethylmaleimide‐sensitive factor attachment protein (SNAP) receptors (SNAREs), which are key components of the cellular membrane fusion machinery are aberrantly sequestered in cholesterol‐enriched regions of LSD endolysosomal membranes. This abnormal spatial organization locks SNAREs in complexes and impairs their sorting and recycling. Importantly, reducing membrane cholesterol levels in LSD cells restores normal SNARE function and efficient lysosomal fusion. Our results support a model by which cholesterol abnormalities determine lysosomal dysfunction and endocytic traffic jam in LSDs by impairing the membrane fusion machinery, thus suggesting new therapeutic targets for the treatment of these disorders.