Guanylate Cyclase Activity in Dictyostelium discoideum and Its Increase during Cell Development

Following consumption of the food supply, cells of the cellular slime mould Dictyostelium discoideum aggregate and form a multicellular organism. The mechanism for cell aggregation is chemotaxis. The chemotactic signal in D. discoideum is released periodically from aggregation centers and propagated from cell to cell. cAMP mediates cell aggregation by acting as chemotactic attractant and as propagator of the signal. cAMP signals are measured by cell-surface receptors. Recent evidence indicates a role for cGMP during cAMP-mediated cell aggregation in D. discoideum .
During cell differentiation to aggregation competence, cAMP binding sites appear at the cell surface, and the activity of the enzymes adenylate cyclase and phosphodiesterase increases several-fold. In the present work we investigate the synthesis of cGMP in D. discoideum . Conditions for the assay of guanylate cyclase in cell homogenates are described. Guanylate cyclase activity was followed during cell differentiation to aggregation competence and found to increase fourfold. These results indicate that cGMP is involved in cell differentiation of D. discoideum . In contrast to adenylate cyclase, which is activated by cAMP, guanylate cyclase was under our conditions activated neither by cAMP, nor by folic acid.     

Nature of 'Pollinator' Effect in Potato (Solanum tuberosum L.) Haploid Production

Haploids (2n =24) of the common tetraploid (2n=48) potato (SolanumtuberosumL.) provide promising material for attacking many problemsconcerned with the genetics, cytogenetics and breeding of thisspecies. Interspecific 4xx2xcrosses betweenSolanum tuberosumgp.Andigenaorgp.Tuberosumcultivars as pistillate parents andSolanum tuberosumgp.Phurejaassource of pollen (hereafter ‘pollinator’) have beenused to produce maternally derived haploids through parthenogenesis.This paper discusses the nature of the ‘pollinator’effect in haploid extraction. The ‘pollinator’ hada significant effect on haploid frequencies following 4xx2xcrosses.The ‘pollinator’ effect seems to operate via theendosperm, in which haploid (n=2x) embryos are associated withhexaploid endosperm. A superior ‘pollinator’ appearsto have its effect by contributing two haploid (n) gametes tothe central cell. 2n pollen; double fertilization; endosperm; ploidy manipulations; Solanum tuberosum     

Effects of altered α‐ and β‐branch carotenoid biosynthesis on photoprotection and whole‐plant acclimation of Arabidopsis to photo‐oxidative stress

Functions of α‐ and β‐branch carotenoids in whole‐plant acclimation to photo‐oxidative stress were studied in Arabidopsis thaliana wild‐type (wt) and carotenoid mutants, lut ein deficient (lut2, lut5), n on‐p hotochemical q uenching1 (npq1) and s uppressor of z eaxanthin‐l ess1 (szl1) npq1 double mutant. Photo‐oxidative stress was applied by exposing plants to sunflecks. The sunflecks caused reduction of chlorophyll content in all plants, but more severely in those having high α‐ to β‐branch carotenoid composition (α/β‐ratio) (lut5, szl1npq1). While this did not alter carotenoid composition in wt or lut2, which accumulates only β‐branch carotenoids, increased xanthophyll levels were found in the mutants with high α/β‐ratios (lut5, szl1npq1) or without xanthophyll‐cycle operation (npq1, szl1npq1). The PsbS protein content increased in all sunfleck plants but lut2. These changes were accompanied by no change (npq1, szl1npq1) or enhanced capacity (wt, lut5) of NPQ. Leaf mass per area increased in lut2, but decreased in wt and lut5 that showed increased NPQ. The sunflecks decelerated primary root growth in wt and npq1 having normal α/β‐ratios, but suppressed lateral root formation in lut5 and szl1npq1 having high α/β‐ratios. The results highlight the importance of proper regulation of the α‐ and β‐branch carotenoid pathways for whole‐plant acclimation, not only leaf photoprotection, under photo‐oxidative stress.     

Does detritus quality predict the effect of native and non‐native plants on the performance of larval amphibians?

1. The lack of consistent differences between the traits of native and non‐native plant species makes it difficult to make general predictions about the ecological impact of invasive plants; however, the increasing number of non‐native plants in many habitats makes the assessment of the impact of each individual species impracticable. General knowledge about how specific plant traits are linked to their effects on communities or ecosystems may be more useful for predicting the effect of plant invasions. Specifically, we hypothesised that higher carbon‐to‐nitrogen ratio (C:N) and percent lignin in plant detritus would reduce the rate of development and total mass at metamorphosis of tadpoles, resulting in lower metamorph production (total fresh biomass) and amphibian species richness. 2. To test these hypotheses, we raised five species of tadpoles in mesocosms containing senescent leaves of three common native and three common non‐native wetland plants that varied in C:N ratio and % lignin. 3. Leaf mass loss, total metamorph production and the number of species that metamorphosed declined as a function of increasing C:N ratio of plant leaves. Plant lignin content was not related to the production of metamorphs or the number of species that metamorphosed. The percentage of wood frog (Lithobates sylvaticus) and American toad (Anaxyrus americanus) tadpoles reaching metamorphosis declined as a function of increasing plant C:N ratio. Mean time to metamorphosis increased and mean mass at metamorphosis declined as a function of increasing plant C:N ratio. Tadpole performance and metamorph diversity and production (biomass) were similar between native and non‐native plant species with similar C:N ratio in leaves. Percent lignin was not a significant predictor of tadpole performance. 4. Our results show that the impact of a plant invasion on tadpole performance could depend on differences between the quality of the detritus produced by the invading species and that of the native species it replaces. We suggest that plant community changes that lead to dominance by more recalcitrant plant species (those with higher leaf C:N ratio) may negatively affect amphibian populations.     

An integrative approach to species discovery in odonates: from character‐based DNA barcoding to ecology

Modern taxonomy requires an analytical approach incorporating all lines of evidence into decision‐making. Such an approach can enhance both species identification and species discovery. The character‐based DNA barcode method provides a molecular data set that can be incorporated into classical taxonomic data such that the discovery of new species can be made in an analytical framework that includes multiple sources of data. We here illustrate such a corroborative framework in a dragonfly model system that permits the discovery of two new, but visually cryptic species. In the African dragonfly genus Trithemis three distinct genetic clusters can be detected which could not be identified by using classical taxonomic characters. In order to test the hypothesis of two new species, DNA‐barcodes from different sequence markers (ND1 and COI) were combined with morphological, ecological and biogeographic data sets. Phylogenetic analyses and incorporation of all data sets into a scheme called taxonomic circle highly supports the hypothesis of two new species. Our case study suggests an analytical approach to modern taxonomy that integrates data sets from different disciplines, thereby increasing the ease and reliability of both species discovery and species assignment.     

Mitochondrial phylogeny of Arvicolinae using comprehensive taxonomic sampling yields new insights

Comprehensive taxonomic sampling can vastly improve the accuracy of phylogenetic reconstruction. Here, we present the most inclusive phylogenetic analysis of Arvicolinae (Mammalia, Rodentia) to date, combining all published cytochrome  b gene sequences of greater than 1097 bp and new sequences from two monotypic genera. Overall, the phylogenetic relationships between 69 species of voles and lemmings, representing 18 genera and 10 tribes, were studied. By applying powerful modern approaches to phylogenetic reconstruction, such as maximum likelihood and Bayesian analysis, we provide new information on the early pulse of evolution within the Arvicolinae. While the position of two highly divergent lineages, Phenacomys and Ondatra , could not be resolved, the tribe Lemmini, appeared as the most basal group of voles. The collared lemmings (Dicrostonychini) grouped together with all of the remaining tribes. The two previously unstudied monotypic genera Dinaromys and Prometheomys form a moderately well-supported monophyletic clade, possibly a sister group to Ellobius (Ellobiusini). Furthermore, with one exception, all tribes ( sensu Musser & Carleton, 2005) proved to be monophyletic and can thus be regarded as meaningful evolutionary entities. Only the tribe Arvicolini emerged as paraphyletic in both analyses because of the unresolved phylogenetic position of Arvicola terrestris . Steppe voles of the genus Lagurus were solidly supported as a sister group to the Microtus and allies clade.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 825–835.     

In Vitro Cultivation of the Vascular Phase of Sarcocystis singaporensis

To establish an in vitro culture system for the precystic phase of Sarcocystis singaporensis, we initially tested various excysting fluids for sporocysts. An excysting fluid containing 2.5% bovine taurocholate and 10% bile of the specific intermediate host, Rattus norvegicus, in RPMI medium was the most suitable resulting in excystation of 80% of the sporozoites. Subsequently, we identified brain endothelial cells and pneumonocytes of the rat to promote growth of sporozoites to schizonts. Hepatoma, fibroblastic, or myoblastic cells were not suitable for the parasite's development. First-generation schizonts were seen at days 3-10 postinoculation (PI); a distinct second peak of schizogonic development only occurred in endothelial cells at days 14-18 PI. First-generation schizonts were 26.0 (± 3.8) μm in diameter and contained 32-50 merozoites, second-generation schizonts measured 34.4 (± 10.6) μm and contained 54-72 merozoites. Merozoite yield at large-scale culture conditions (75 cm² flasks) using pneumonocytes as host cells was relatively low. Ultrastructurally, sporozoites and merozoites were quite similar to corresponding stages of other Sarcocystis species. With regard to host cell specificity and developmental kinetics, in vitro cultivation showed close similarities to the situation in vivo.