Unravelling the Leishmania genome

The past few years have seen significant advances in our understanding of eukaryotic genomes. In the field of parasitology, this is best exemplified by the application of genome mapping techniques to the study of genome structure and function in the protozoan parasite, Leishmania. Although much is known about the organism and the diseases it causes, molecular genetics has only recently begun to play a major part in elucidating some of the unusual characteristics of this interesting parasite. Mapping of the small (35 Mb) genome and determination of the functional role of genes by the application of in vitro homologous gene targeting techniques are revealing novel avenues for the development of prophylactic measures.     

Some characteristics of the prostaglandin synthesizing system in rabbit kidney microsomes.

The prostaglandin synthesizing system in rabbit kidney microsomes was characterised using a radiometric assay. Three prostaglandins (F2alpha, E2 and D2) were formed form (1-14C)arachidonic acid, a small amount of prostaglandin A2 was also detected but this was formed non-enzymatically. Biosynthesis was stimulated by reduced-glutathione and 1-adrenaline and was inhibited by aspirin-like drugs. The enzyme system was sensitive to small changes in pH. There were substantial differences in drug sensitivity and optimal reaction conditions between this prostaglandin synthesizing system and the one from bovine seminal vesicles.     

Physiological response of the unicellular green alga Chlorococcum submarinum to rapid changes in salinity

Cell volumes and intracellular concentrations of major solutes of Chlorococcum submarinum were determined before and after salinity shocks. Cells were found to shrink in size by about 30% following changes from 0.1 to 0.5 M NaCl, there was a transitory increase in sodium concentration and more permanent increases in concentrations of potassium, proline and glycerol (the major osmolyte). Conversely, cells doubled in size after the reciprocal downshock, there was rapid loss of about 70% of the cells' glycerol to the medium, a much smaller loss of cellular potassium and a steady disappearance of proline from the cells. The respiratory and photosynthetic responses to salinity fluctuations were also studied. Salinity downshocks stimulated respiration by 30% and inhibited photosynthesis by 16% within 5 min, but within 2 h these rates were identical to control rates. Upshocks caused a slight inhibition of respiration, but decreased photosynthesis by 40% within 5 min and recovery took 2 h. Downshocks had little effect on chlorophyll fluorescence, however, Fo strongly increased and both Fm and Fv/Fm declined within 5 min of salinity increases. This is consistent with a decrease in efficiency of PS2. Ecological and metabolic implications of the results are discussed.Abbreviations DMSO dimethyl sulphoxide - Hepes N-[2-hydroxyethyl]piperazine-N-2-ethane sulphonic acid - TCA trichloroacetic acid - Tris tris[hydroxymethyl]aminoethane     

Inter- and intra-species intercropping of barley cultivars and legume species,as affected by soil phosphorus availability

Aims

Intercropping can improve plant yields and soil phosphorus (P) use efficiency. This study compares inter- and intra-species intercropping, and determines whether P uptake and shoot biomass accumulation in intercrops are affected by soil P availability.

Methods

Four barley cultivars (Hordeum vulgare L.) and three legume species (Trifolium subterreneum, Ornithopus sativus and Medicago truncatula) were selected on the basis of their contrasting root exudation and morphological responses to P deficiency. Monocultures and barley-barley and barley-legume intercrops were grown for 6 weeks in a pot trial at very limiting, slightly limiting and excess available soil P. Above-ground biomass and shoot P were measured.

Results

Barley-legume intercrops had 10–70% greater P accumulation and 0–40% greater biomass than monocultures, with the greatest gains occurring at or below the sub-critical P requirement for barley. No benefit of barley-barley intercropping was observed. The plant combination had no significant effect on biomass and P uptake observed in intercropped treatments.

Conclusions

Barley-legume intercropping shows promise for sustainable production systems, especially at low soil P. Gains in biomass and P uptake come from inter- rather than intra-species intercropping, indicating that plant diversity resulted in decreased competition between plants for P.

     

Auxin-Cytokinin Interactions in Wild-Type and Transgenic Tobacco

Cytokinins and auxins are important regulators of plant growthand development, but there is incomplete and conflicting evidencethat auxins affect cytokinin metabolism and vice versa. We haveinvestigated these interactions in Nicotiana tabacum L. by separatein planta manipulation of levels of the hormones followed byanalysis of the induced changes in the metabolism of the otherhormone. Cytokinin-overproducing plants (expressing the Agrobacte-riumtumefaciens ipt gene) had lower than wild-type levels of freeIAA, and reduced rates of IAA synthesis and turnover, but therewere no differences in the profiles of metabolites they producedfrom fed IAA. Similarly, auxin-overproducing plants (expressingthe A.tumefaciens iaaM and iaaH genes), had lower levels ofthe major cytokinins than wild-type plants and lower cytokininoxidase activity, but there were no differences in the profilesof metabolites they produced from fed cytokinins. The data demonstratethat cytokinin or auxin overproduction decreases the contentof the other hormone, apparently by decreasing its rate of synthesisand/or transport, rather than by increasing rates of turnoveror conjugation. Implications for the importance of cytokinin: auxin ratios in plant development are considered. (Received September 24, 1996; Accepted December 4, 1996)     

Individual Variation in Advertisement Calls of Territorial Male Green Frogs, Rana clamitans: Implications for Individual Discrimination

Individuals of many territorial species discriminate between familiar territorial neighbors and unfamiliar strangers based on individual differences in acoustic signals. Many anuran amphibians are territorial and use primarily acoustic communication during social interactions, but evidence for acoustically mediated individual discrimination is available only for one species. As a first step in research designed to investigate individual discrimination in a second species of territorial frog, we examined patterns of within-male and among-male variability in 198 advertisement calls of 20 male green frogs, Rana clamitans . The aim was to determine which acoustic properties could be used by males to recognize their territorial neighbors and to estimate limits of reliability afforded by these properties for identifying different neighbors. All of the call properties that we examined exhibited significant inter-individual variation. Discriminant function analyses assigned between 52% and 100% of calls to the correct individual, depending on sample size and the call properties included in the model. This suggests that there is sufficient among-male variability to statistically identify individuals by their advertisement calls. The call properties of fundamental frequency and dominant frequency contributed the most towards discrimination among individuals. Based on their natural history and behavior and the results reported here, we suggest that male green frogs likely discriminate between strangers and adjacently territorial neighbors based on individual variation in advertisement calls.     

Interactions between mucopolysaccharides and cationic polypeptides in aqueous solution: hyaluronic acid, heparitin sulfate, and keratan sulfate

Circular dichroism spectroscopy has been used to study the interactions of hyaluronic acid, heparitin sulfate, and keratan sulfate with cationic polypeptides. The results indicate that the presence of these mucopolysaccharides has an effect in the conformation of poly(L -lysine) and poly(L -arginine), such that the former adopts the “random” form and the latter takes up the α-helical conformation, rather than the “charged coil” form expected at neutral pH. The relative strengths of the interactions can be judged from the melting temperatures above which they are disrupted. Both the stoichiometry and the strength of the interactions depend on the position, number, and type of anionic groups attached to the polysaccharide backbone. Such considerations place the six common mucopolysaccharides in order of increasing strength of interaction: hyaluronic acid < chondroitin 4-sulfate < heparitin sulfate < chondroitin 6-sulfate < keratan sulfate ? dermatan sulfate. These differences should be paralleled by differences in the interaction of the mucopolysaccharides with collagen and fibrous proteins.