Factors controlling the population dynamics of the clonal helophyte Ranunculus lingua

Abstract. Two marginal and two central populations of the pseudo-annual aquatic plant Ranunculus lingua were studied over four years. The main purpose was to quantify potentially influential abiotic and biotic factors and to derive predictions about life-history differences between the populations. Variation in abundance and height of R. lingua ramets at different depths were related to water-level fluctuations, to abundance of other helophyes (emergent macrophytes), and to the occurrence of invertebrate grazing and fungal pathogens. Clear differences between marginal and central populations were shown in the depth distribution of ramet numbers and ramet heights, as well as in the dynamic patterns, where marginal populations had a higher flux of ramets. These patterns and regression analyses indicated that abiotic factors have a greater influence in marginal populations, whereas biotic factors are more important in central populations. It is suggested that marginal habitats for R. lingua would favour life-histories with a high reproductive capacity, whereas a large size of ramet would be the most important life-history feature in central habitats. This was supported by the fact that ramets in marginal populations, in spite of their smaller size, produced higher number of rhizomes than ramets in central populations. Variation in regional abundance was finally related to differences in demographic processes and dispersal potential between the populations.     

A new species of Croton (Euphorbiaceae) from Somalia

Croton crispatus , sp. nov., from Acacia-Commiphora bushland on sand in central Somalia, is described and illustrated.     

Acacia ochracea (Leguminosae-Mimosoideae), a new species from Somalia

Acacia ochracea , a new species in the A. Senegal complex, is described and illustrated. It is a common and conspicuous tree over large areas in the western Bay Region and in the Gedo Region in SW Somalia.     

New or noteworthy species of Leguminosae in NE tropical Africa

The following new species are described: Chamaecrista dunensis (Somalia), Acacia densispina (Somalia), A. flagellaris (Somalia), Tephrosia karkarensis (Somalia), T. scopulata (Somalia), Indigofera ancistrocarpa (Kenya), I. curvirostrata (Ethiopia), I. hiranensis (Somalia), I. karinensis (Somalia), I. kucharii (Somalia), I. nugalensis (Somalia), I. pellucida (Kenya, Somalia), I. sabulosa (Ethiopia, Somalia), I. sessilis (Somalia), I. ienuirostris (Somalia), Rhynchosia megalocalyx (Somalia), Crotalaria allophylla (Somalia), C. intricata (Somalia), C. warfae (Somalia), and Coronilla somalensis (Somalia). 2n = 22 is reported in Tephrosia karkarensis. Cassia somalensis, Acacia puccioniana, Sophora somalensis , and Crotalaria sennii are reduced to synonyms of respectively Senna hookeriana, Dichrostachys kirkii, Millettia usaramensis and Crotalaria boranica subsp. trichocarpa . Thirty-seven taxa are reported from Somalia for the first time, including Ptycholobium biflorum , known previously only from Southern Africa. Crotalaria pieropoda , known previously only from Socotra, is reported from Somalia and Oman. Neptunia oleracea and Vatovaea pseudolablab are new generic records for respectively Ethiopia and Oman. The fruits of Indigofera boranica are described. Vigna somaliensis and an allied species are discussed. Rhynchosia gansole is lectotypified and its flowers and fruits are described.     

Total chemical synthesis and NMR characterization of the glycopeptide tx5a, a heavily post-translationally modified conotoxin, reveals that the glycan structure is alpha-D-Gal-(1-->3)-alpha-D-GalNAc.

The 13-amino acid glycopeptide tx5a (Gla-Cys-Cys-Gla-Asp-Gly-Trp*-Cys-Cys-Thr*-Ala-Ala-Hyp-OH, where Trp* = 6-bromotryptophan and Thr* = Gal-GalNAc-threonine), isolated from Conus textile, causes hyperactivity and spasticity when injected intracerebral ventricularly into mice. It contains nine post-translationally modified residues: four cysteine residues, two gamma-carboxyglutamic acid residues, and one residue each of 6-bromotryptophan, 4-trans-hydroxyproline and glycosylated threonine. The chemical nature of each of these has been determined with the exception of the glycan linkage pattern on threonine and the stereochemistry of the 6-bromotryptophan residue. Previous investigations have demonstrated that tx5a contains a disaccharide composed of N-acetylgalactosamine (GalNAc) and galactose (Gal), but the interresidue linkage was not characterized. We hypothesized that tx5a contained the T-antigen, beta-D-Gal-(1-->3)-alpha-D-GalNAc, one of the most common O-linked glycan structures, identified previously in another Conus glycopeptide, contalukin-G. We therefore utilized the peracetylated form of this glycan attached to Fmoc-threonine in an attempted synthesis. While the result-ing synthetic peptide (Gla-Cys-Cys-Gla-Asp-Gly-Trp*-Cys-Cys-Thr*-Ala-Ala-Hyp-OH, where Trp* =6-bromotryptophan and Thr* = beta-D-Gal-(1-->3)-alpha-D-GalNAc-threonine) and the native peptide had almost identical mass spectra, a comparison of their RP-HPLC chromatograms suggested that the two forms were not identical. Two-dimensional 1H homonuclear and 13C-1H heteronuclear NMR spectroscopy of native tx5a isolated from Conus textile was then used to determine that the glycan present on tx5a indeed is not the aforementioned T-antigen, but rather alpha-D-Gal-(1-->3)-alpha-D-GalNAc.     

Calliandra (Leguminosae) in continental Africa

The mainly neotropical genus Calliandra Benth. (Leguminosae–Mimosoideae–Ingeae) is reported for the first time as native in continental Africa. There are two species known, C. gilbertii Thulin & Hunde sp. nov. in E Kenya and Somalia and C. redacta (J. H. Ross) Thulin & Hunde comb. nov. in South Africa near the Namibia border. On pollen morphological grounds they are supposed to be most related to certain neotropical species but the pollen does not agree entirely with any previously known group of the genus. The distribution of C gilbertii and C. redacta stresses the phytogeographical link between the arid zones of northern and southern Africa.     

Analysis of rpsD mutations in Escherichia coli

Summary A certain proportion of protein S7 exists in an altered form in E. coli rpsD (S4) mutants. Depending on the type of S4 mutation involved, two different forms of the altered S7 can be distinguished. The unusual form is longer than normal S7 by about 500 daltons due to extra material at the carboxyl end of the protein. It is suggested that a mutationally altered S4 might lower the efficiency of termination during translation of the messenger for S7. This results in an increased frequency of translational read-through, which gives the observed longer forms of S7. Data are interpreted to mean that one class of S4 mutants might suppress UGA and UAG whereas another class only suppresses UGA.     

Fluorescence-microscopical demonstration of a population of gastro-intestinal nerve fibres with a selective affinity for Quinacrine

Summary A population of nerve fibres in the gastro-intestinal tract of mice showing a high affinity for quinacrine was revealed by fluorescence microscopy. Similar results were obtained in rats and guinea pigs. Whole-mounts of sheets of the smooth muscle layer following incubation in 10^-6-10^-7 M quinacrine for 15–60 min revealed fine fluorescent varicose nerve fibers in the myenteric plexus of Auerbach both around nerve cell bodies and in the interconnecting strands. Many fibers were also present between the strands of the plexus, especially running parallel to the circular muscle layer. Such fibers were not seen in similarly quinacrine-incubated irides. A proportion of the cell bodies in Auerbach's plexus also showed quinacrine accumulation. These cells were apparently smaller neurons, sometimes with fluorescent processes. Intraperitoneal injections of quinacrine failed to demonstrate nerve fibers, but some cell bodies in Auerbach's plexus were positive. Subsequent paraformaldehyde treatment for monoamine visualization showed persistent adrenergic nerve terminals in the intestine and iris. These nerves seemed to be fewer and had a more yellow fluorescence than normally. The identity of the quinacrine-positive fibers is discussed with respect to recent suggestions that purinergic, substance P, enkephalin, and somatosin-containing nerves, in addition to adrenergic and cholinergic nerves, are present in the gut wall.Supported by the Swedish Medical Research Council (04X-03185). Magnus Bergvalls Stiftelse and Karolinska Institutets Fonder. For generous gifts of Mepacrine we thank Winthrop, Skärholmen, Stockholm, Sweden. The skilful technical assistance of Miss Gerd Boetius and Miss Maud Eriksson is gratefully acknowledged