Behaviour of drifting insect larvae

The larval drift behaviour of 23 species representing Ephemeroptera, Plecoptera and Trichoptera was investigated in the laboratory using different current regimes. Mayfly nymphs often performed swimming, while caddis larvae were reluctant to do so. Stonefly nymphs were intermediate. In mayflies swimming seemed to be used to reach the substrate as soon as possible. In contrast most stonefly nymphs by swimming prolonged the time spent in the water column. Modes of swimming and sinking posture differed markedly between the orders. Living passively sinking animals often reached bottom faster than dead control specimens, so consequently behaviour did not always express itself in activity. Some caddis larvae spun adherent anchor lines. Differences among taxa seemed more important in explaining swimming activity compared to preferred habitats (as stream, river and lake) in each species. However, observed differences among closely related species indicated subtle differences related to microhabitat to be of profound importance in explaining the alternative behavioural strategies used.     

Radiation inactivation analysis of influenza virus reveals different target sizes for fusion, leakage, and neuraminidase activities

The size of the functional units responsible for several activities carried out by the influenza virus envelope glycoproteins was determined by radiation inactivation analysis. Neuraminidase activity, which resides in the glycoprotein NA, was inactivated exponentially with an increasing radiation dose, yielding a target size of 94 +/- 5 kilodaltons (kDa), in reasonable agreement with that of the disulfide-bonded dimer (120 kDa). All the other activities studied are properties of the HA glycoprotein and were normalized to the known molecular weight of the neuraminidase dimer. Virus-induced fusion activity was measured by two phospholipid dilution assays: relief of energy transfer between N-(7-nitro-2,1,3-benzoxadiazol-4-yl)dipalmitoyl-L-alpha- phosphatidylethanolamine (N-NBD-PE) and N-(lissamine rhodamine B sulfonyl)-dioleoyl-L-alpha-phosphatidylethanolamine (N-Rh-PE) in target liposomes and relief of self-quenching of N-Rh-PE in target liposomes. Radiation inactivation of fusion activity proceeded exponentially with radiation dose, yielding normalized target sizes of 68 +/- 6 kDa by assay i and 70 +/- 4 kDa by assay ii. These values are close to the molecular weight of a single disulfide-bonded (HA1 + HA2) unit (75 kDa), the "monomer" of the HA trimer. A single monomer is thus inactivated by each radiation event, and each monomer (or some part of it) constitutes a minimal functional unit capable of mediating fusion. Virus-induced leakage of calcein from target liposomes and virus-induced leakage of hemoglobin from erythrocytes (hemolysis) both showed more complex inactivation behavior: a pronounced shoulder was present in both inactivation curves, followed by a steep drop in activity at higher radiation levels.(ABSTRACT TRUNCATED AT 250 WORDS)     

Voltage-dependent channel formation by rods of helical polypeptides

Summary The voltage-dependence of channel formation by alamethicin and its natural analogues can be described by a dipole flip-flop gating model, based on electric field-induced transbilayer orientational movements of single molecules. These field-induced changes in orientation result from the large permanent dipole moment of alamethicin, which adopts -helical conformation in hydrophobic medium. It was, therefore, supposed that the only structural requirement for voltage-dependent formation of alamethicin-type channels might be a rigid lipophilic helical segment of minimum length.In order to test this hypothesis we synthesized a family of lipophilic polypeptides—Boc-(Ala-Aib-Ala-Aib-Ala) _n -OMe,n=1–4—which adopt -helical conformation forn=2–4 and studied their interaction with planar lipid bilayers. Surprisingly, despite their large difference in chain length, all four polypeptides showed qualitatively similar behavior. At low field strength of the membrane electric field these polypeptides induce a significant, almost voltage-independent increase of the bilayer conductivity. At high field strength, however, a strongly voltage-dependent conductance increase occurs similar to that observed with alamethicin. It results from the opening of a multitude of ion translocating channels within the membrane phase.The steady-state voltage-dependent conductance depends on the 8^th–9^th power of polypeptide concentration and involves the transfer of 4–5 formal elementary charges. From the power dependences on polypeptide concentration and applied voltage of the time constants in voltage-jump current-relaxation experiments, it is concluded that channels could be formed from preexisting dodecamer aggregates by the simultaneous reorientation of six formal elementary charges. Channels exhibit large conductance values of several nS, which become larger towards shorter polypeptide chain length. A mean channel diameter of 19 Å is estimated corresponding roughly to the lumen diameter of a barrel comprised of 10 -helical staves. Similar to experiments with the N-terminal Boc-derivative of alamethicin we did not observe the burst sequence of nonintegral conductance steps typical of natural (N-terminal Ac-Aib)-alamethicin. Saturation in current/voltage curves as well as current inactivation in voltage-jump current-relaxation experiments are found. This may be understood by assuming that channels are generated as dodecamers but, while reaching the steady state, reduce their size to that of an octamer or nonamer. We conclude that the overall behavior of these synthetic polypeptides is very similar to that of alamethicin. They exhibit the same concentration and voltage-dependences but lack the stabilizing principle of resolved channel states characteristic of alamethicin.     

Virulence genes are carried by a megaplasmid of the plant pathogen Pseudomonas solanacearum

Summary A class of avirulent mutants of the plant pathogenic bacterium Pseudomonas solanacearum, strain GMI1000, resistant to acridine orange (Acr^r), harbour a deletion of over 85 kb in their genome. This deletion affects, a1,000 kb megaplasmid which has previously been shown to be present in most of the strains of this species. In addition at least 11 out of 13 independent Tn5 insertions, leading to loss of virulence, are located on the megaplasmid. Nine of them are present in the region which is deleted from the Acr^r mutants. These results suggest that the majority of virulence genes identified so far are plasmid borne.     

Identification of host range determinants in the Rhizobium species MPIK3030

Summary R. meliloti primarily nodulates Medicago sativa but cannot nodulate Macroptilium atropurpureum. By introducing an 11.4 kb region into R. meliloti from the Symplasmid of Rhizobium strain MPIK3030, the host range of the R. meliloti transconjugants were shown to be extended to M. atropurpureum, one of the hosts of MPIK3030 but not normally nodulated by R. meliloti. The region responsible for host range extension was isolated by mass conjugating a clone bank from MPIK3030 into the R. meliloti wild type, and subsequent screening for nodulation on M. atropurpureum. Using deleted derivatives of a plasmid reisolated from endosymbiotic bacteria, the host range region was further narrowed down to three EcoRI fragments. Tn5 mutagenesis allowed the isolation of three discrete regions on an 11.4 kb section, which are involved in the extension of host range to M. atropurpureum. Finally, complementation experiments performed with R. meliloti common nod and hsn mutants indicated that none of the genes involved in the early steps of nodulation, including host-range functions, can be complemented by genes carried on the 11.4 kb fragment derived from MPIK3030.     

Polyester Wadding for Specimen Orientation During Embedding in Methacrylates

Polyester fibers are not dissolved by either glycol methacrylate or methyl methacrylate. Commercial polyester wadding is consequently an advantageous material to use in getting precise orientation of tissue specimens during embedding in methacrylate.     

Permanent Preservation of Whole Alizarin Red S Skeletons by Clearing and Embedding in Polyester Resins

A one-step clearing and embedding procedure for alizarin red S stained skeletons is described. Embryos are fixed in formalin, skinned and eviscerated. After staining in a 10 mg/liter solution of alizarin red S in 5% aqueous KOH, specimens are dehydrated in a graded series of acetone-polyester monomer solutions. Finally, the specimens are embedded at room temperature in the polyester resin. A special reusable metallic mold is described for embedment of large fetuses. Specimens previously cleared in glycerol can be processed with this method.     

Analyse von zwei Legumin-Genfamilien der Ackerbohne (Vicia faba L.)

DNA clones representing two subfamilies A and B of legum in genes and a recombinant phage containing a complete legumin B gene have been isolated and characterized by DNA sequencing. A DNA fragment harbouring the legumin B gene and adjacent sequences was used for Ti-mediated transfer into tobacco cells.     

Male-like behaviour in an all-female lizard: relationship to ovarian cycle

A quantitative analysis of the relationship between pseudocopulatory behaviour and the ovarian cycle in the parthenogenetic lizard Cnemidophorus uniparens indicates (1) that this behaviour is frequently and regularly expressed by captive individuals, and (2) that the sexual role, either male-like or female-like, exhibited by an animal is correlated with its ovarian state. The expression of female-like behaviour patterns was associated with and primarily limited to the vitellogenic stage of the cycle. Male-like behaviour patterns occurred most frequently during post-ovulatory stages but was not limited to these stages. Neither behavioural role was ever expressed by non-reproductive individuals. Reproductive individuals often alternated in assuming the female-like and male-like roles during the progress of the ovarian cycle. These observations suggest that pseudosexual behaviour is hormonally activated in this species. However, it also appears that the prevailing social situation is an important factor determining which behavioural role is taken. This work strengthens the hypothesis that pseudosexual behaviour in all-female lizards occurs as the result of natural selection.     

G-11 staining in Turner's syndrome with mos 45,X/46,X,r(?)

Mos 45,X/46,X,r(?) in 4 patients with Turner's syndrome and no signs of virilization, and in one pair of monozygotic twins, one of them with clitoral hypertrophy, was studied using combined cytogenetic techniques and specially G-11 staining for the characterization of the X or Y origin of the rings. In all 6 patients the ring was G-11 positive, attesting its Y origin. Both twins were operated and bilateral streak gonads with a bilateral nodule of testicular tissue were found. Similar small rings were also studied in one patient with mos 46,XX/46,X,r(X) and in one nonvirilized Turner's syndrome patient with a larger ring; in these two cases the ring was G-11 negative. It seems that the small rings occasionally found in Turner's syndrome are more frequently from Y origin and therefore prophylactic gonadectomy should be considered.