Cytogenetic study of F1 hybrids betweenCrepis dinarica andCrepis froelichiana (Asteraceae)

Crepis dinarica andC. froelichiana are two closely related species of theC. praemorsa complex. Even though they exhibit the same chromosome number (2n = 8) and similar idiogram shape, they differ widely in quantity and distribution of heterochromatin bands. The hybrids between these two species comprise three morphological types. Parental genomes were distinguished in hybrids by Giemsa differential staining (C-banding). Although meiosis presents only a few abnormalities (about 2.4%), the percentage of aborted pollen grains is very high (90%).     

Enhancement of lysophospholipase activity with Trichinella spiralis antigen: evidence for cell cooperation

Murine lymphocytes, neutrophils, macrophages and eosinophils were assayed for lysophospholipase in order to determine the cellular source of the enzyme. The eosinophil was the only cell that demonstrated a positive reaction for the enzyme. The role of other cells and/or antigen in production of the enzyme by the eosinophil was also investigated. Results demonstrated that eosinophils cultured with both Trichinella spiralis antigen and other leukocytes (lymphocytes and/or macrophages) yielded enzyme activities significantly greater than did eosinophils cultured alone or with only antigen. More specific experiments showed that T-lymphocytes were the cells responsible for influencing the eosinophils' production of lysophospholipase in the presence of antigen, and that their influence was enhanced by the presence of macrophages. These results suggest that increased lysophospholipase activity present in parasitized tissue is not only due to an increased number of eosinophils infiltrating parasitized tissues, but is also due to each eosinophil synthesizing more of the enzyme for release. The necessity for antigen and other cells suggests a need for cell cooperation in the production of the enzyme, specifically T-lymphocytes and macrophage interaction with the eosinophil.     

Hemagglutination Inhibition with Arboviruses: Relationship Between Titers and Source of Erythrocytes

Antigens for Grand Arbaud, Hazara, and California arboviruses were able to agglutinate goose and either dog, hamster and guinea pig, or hamster red blood cells (RBC) to the same titer at the same pH; in hemagglutination-inhibition (HI) tests, titers for homologous and related sera were the same with these different types of RBC or occasionally one dilution higher with the mammalian cells. Antigens for St. Louis encephalitis and Eastern equine encephalitis viruses required use of lower antigen dilutions with human, guinea pig, and hamster RBC than with goose RBC. The results of comparative HI testing with these latter antigens and types of RBC indicate that HI titer is not directly related to the antigen dilution used with different types of RBC.     

Effect of immune system imagery on secretory IgA

This study was an investigation of the effects of physiologically-oriented mental imagery on immune functioning. College students with normal medical histories were randomly selected to one of three groups. Subjects in Group 1 participated in short educational training on the production of secretory immunoglobulin A. They were then tested on salivary IgA, skin temperature, and the Profile of Mood States (POMS) before and after listening to a 17-minute tape of imagery instructions with specially composed background entrainment music designed to enhance imagery. Subjects in Group 2 (placebo controls) listened to the same music but received nor formal training on the immune system. Group 3 acted as a control and subjects were tested before and after 17 minutes of no activity. Treatment groups listened to their tapes at home on a bi-daily basis for six weeks All groups were again tested at Weeks 3 and 6. Secretory IgA was analyzed using standard radial immunodiffusion techniques. Repeated measures analyses of variance with planned orthogonal contrasts were used to evaluate the data. Significant overall increases (p<0.05) were found between pre- and posttests for all three trials. Groups 1 and 2 combined (treatment groups) yielded significantly greater increases in sIgA over Group 3 (control) for all three trials. Group 1 (imagery) was significantly higher than Group 2 (music) in antibody production for Trials 2 and 3. Symptomatology, recorded by subjects at Weeks 3 and 6, was significantly lower for three symptoms (rapid heartbeat, breathing difficulty, and jaw clenching), favoring both treatment groups over the control group.     

Functional Expression of P-Glycoprotein in an Immortalised Cell Line of Rat Brain Endothelial Cells, RBE4

Abstract: The presence of P-glycoprotein in the cell plasma membrane limits the penetration of many cytotoxic substances into cells that express the gene product. There is considerable evidence also to indicate that P-glycoprotein is expressed as part of the normal blood-brain barrier in the luminal membranes of the cerebral capillary endothelial cells, where it presumably performs a protective function for the brain. This report describes the functional expression of P-glycoprotein in an immortalised cell line, RBE4, derived from rat cerebral capillary endothelial cells. The expression of P-glycoprotein is demonstrated by western immunoblotting and by immunogold and fluorescent staining with monoclonal antibodies. The cellular accumulation of [³H]colchicine and [³H]vinblastine is investigated and shown to be enhanced by the presence of azidothymidine, chlorpromazine, verapamil, cyclosporin A, and PSC 833 ([3'-keto-Bmt¹]-[Val²]-cyclosporin) at 50 or 100 µ M concentration. It is concluded that the RBE4 cell line is a valuable tool for investigating the mechanisms of P-glycoprotein activity both in the blood-brain barrier and in multidrug resistance in general.     

Pigment interactions in chlorosomes of various green bacteria

Resonance Raman experiments were performed on different green bacteria. With blue excitation, i.e. under Soret resonance or preresonance conditions, resonance Raman contributions were essentially arising from the chlorosome pigments. By comparing these spectra and those of isolated chlorosomes, it is possible to evaluate how the latter retain their native structure during the isolation procedures. The structure of bacteriochlorophyll oligomers in chlorosomes was interspecifically compared, in bacteriochlorophyllc- and bacteriochlorophylle- synthesising bacteria. It appears that interactions assumed by the 9-keto carbonyl group are identical inChlorobium limicola, Chlorobium tepidum, andChlorobium phaeobacteroides. In the latter strain, the 3-formyl carbonyl group of bacteriochlorophylle is kept free from intermolecular interactions. By contrast, resonance Raman spectra unambiguously indicate that the structure of bacteriochlorophyll oligomers is slightly different in chlorosomes fromChloroflexus auranticus, either isolated or in the whole bacteria.     

Trade-offs and synergies between ecosystem productivity and stability in temperate grasslands

Aim

It is crucial to monitor how the productivity of grasslands varies with its temporal stability for management of these ecosystems. However, identifying the direction of the productivity–stability relationship remains challenging because ecological stability has multiple components that can display neutral, positive or negative covariations. Furthermore, evidence suggests that the direction of the productivity–stability relationship depends on the biotic interactions and abiotic conditions that underlie ecosystem productivity and stability. We decipher the relationships between grassland productivity and two components of its stability in four habitat types with contrasting environments and flora.

Location

France.

Time period

2000–2020.

Major taxa

Grassland plant species.

Methods

We used c. 20,000 vegetation plots spread across French permanent grasslands and remotely sensed vegetation indices to quantify grassland productivity and temporal stability. We decomposed stability into constancy (i.e., temporal invariability) and resistance (i.e., maximum deviation from average) and deciphered the direct and indirect effects of abiotic (namely growing season length and nitrogen input) and biotic (namely plant taxonomic diversity, trait diversity and community-weighted mean traits) factors on productivity–stability relationships using structural equation models.

Results

We found a positive relationship between productivity and constancy and a negative relationship between productivity and resistance in all habitats. Abiotic factors had stronger effects on productivity and stability compared with biotic factors. A longer growing season enhanced grassland productivity and constancy. Nitrogen input had positive and negative effects on grassland productivity and resistance, respectively. Trait values affected the constancy and resistance of grassland more than taxonomic and trait diversity, with effects varying from one habitat to another. Productivity was not related to any biotic factor.

Main conclusions

Our findings reveal how vital it is to consider both the multiple components of stability and the interaction between environment and biodiversity to gain an understanding of the relationships between productivity and stability in real-world ecosystems, which is a crucial step for sustainable grassland management.     

Queuosine Biosynthesis Is Required for Sinorhizobium meliloti-Induced Cytoskeletal Modifications on HeLa Cells and Symbiosis with Medicago truncatula

Rhizobia are symbiotic soil bacteria able to intracellularly colonize legume nodule cells and form nitrogen-fixing symbiosomes therein. How the plant cell cytoskeleton reorganizes in response to rhizobium colonization has remained poorly understood especially because of the lack of an in vitro infection assay. Here, we report on the use of the heterologous HeLa cell model to experimentally tackle this question. We observed that the model rhizobium Sinorhizobium meliloti, and other rhizobia as well, were able to trigger a major reorganization of actin cytoskeleton of cultured HeLa cells in vitro. Cell deformation was associated with an inhibition of the three major small RhoGTPases Cdc42, RhoA and Rac1. Bacterial entry, cytoskeleton rearrangements and modulation of RhoGTPase activity required an intact S. meliloti biosynthetic pathway for queuosine, a hypermodifed nucleoside regulating protein translation through tRNA, and possibly mRNA, modification. We showed that an intact bacterial queuosine biosynthetic pathway was also required for effective nitrogen-fixing symbiosis of S. meliloti with its host plant Medicago truncatula, thus indicating that one or several key symbiotic functions of S. meliloti are under queuosine control. We discuss whether the symbiotic defect of que mutants may originate, at least in part, from an altered capacity to modify plant cell actin cytoskeleton.