Seasonal abundance and vertical distribution of mesopelagic calycophoran siphonophores in Monterey Bay, CA

The seasonal abundance and vertical distribution patterns ofa group of small calycophoran siphonophores (principally Chuniphyesmultidentata and Lensia conoidea) were investigated using aremotely operated vehicle (ROV) deployed in Monterey Bay, California.Abundance was assessed along 295 horizontal transects coveringa depth range of 100–1000 m over a three and a half yearperiod. The vertical distribution of the study animals changedseasonally, coupled to the onset and cessation of upwellingin the bay. While numerical abundance peaked after upwelling,there was no significant difference between seasons. The siphonophoreswere more broadly distributed over the depth range sampled duringthe upwelling or Shallow Mixed Layer (SML) period, than duringthe non-upwelling or Deep Mixed Layer (DML) period. There wereno significant differences in abundance or distribution patternsbetween years except in 1993, when there were significantlymore siphonophores observed during the SML period than duringthe DML period. This may reflect effects resulting from the1992–1993 El Niño event. The abundance of thesesiphonophores was negatively correlated with that of Nanomiabijuga, a physonect siphonophore of similar size and feedingbehavior found in the bay. The siphonophores studied here appearfrom preliminary data to migrate vertically, possibly with twoseparately migrating groups.     

Induction of high-frequency somatic embryos in cassava for cryopreservation

Methods for inducing high-frequency somatic embryos in cassava on cotyledons and 33 clonal accessions by the addition of supplementary copper sulphate to the induction medium were investigated. The addition of copper sulphate enhanced primary embryo induction and significantly increased secondary embryo production. All accessions from Latin America (CIAT) were embryogenically competent on medium supplemented with 8 mg l^-1 2,4-dichlorophenoxyacetic acid (2,4-D) plus 1 µM copper sulphate as were 15 of the 18 accessions from Africa. The percentage of calli producing somatic embryos ranged from 7.5% in M. Bra 12 to 100% in M. Col. 1505, while the number of embryos produced per callus ranged from 0.3 in M. Bra 383 to 13.5 in TEK. The frequency of embryo production was dependent on the concentration of copper sulphate. The number of primary embryos produced per callus was also comparatively higher in the medium supplemented with copper sulphate than in the controls. The optimal concentration of copper sulphate for number of embryos produced in most accessions was 5 µM, and at this concentration the number of embryos produced was double that of the controls. Copper sulphate also reduced the maturation time of somatic embryos to 25 days from embryo initiation. High levels of 2,4-D were detrimental to embryo production. Similarly, fragmented embryos incubated in the dark produced more embryos tan those incubated under light conditions. On the basis of these results, the use of cassava somatic embryo micropropagules for germplasm conservation and synthetic seed development seems to be a strong possibility.     

Involvement of the Lipopolysaccharides of Azospirilla in the Interaction with Wheat Seedling Roots

The present study was undertaken to comparatively investigate the attachment capacities of Azospirillum brasilenseSp245 and its lipopolysaccharide-defective Omegon-Km mutants KM018 and KM252, as well as their activities with respect to the alteration of the morphology of wheat seedling root hairs. The adsorption dynamics of the parent Sp245 and mutant KM252 strains of azospirilla on the seedling roots of the soft spring wheat cv. Saratovskaya 29 were similar; however, the attachment capacity of the mutant KM252 was lower than that of the parent strain throughout the incubation period (15 min to 48 h). The mutation led to a considerable decrease in the hydrophobicity of the Azospirillumcell surface. The lipopolysaccharides extracted from the outer membrane of A. brasilenseSp245 and mutant cells with hot phenol and purified by chromatographic methods were found to induce the deformation of the wheat seedling root hairs, the lipopolysaccharide of the parent strain being the most active in this respect. The role of the carbohydrate moiety of lipopolysaccharides in the interaction of Azospirillumcells with plants is discussed.     

Biochemical applications of a synchronously pumped krypton ion dye laser fluorescence system.

A synchronously pumped krypton ion dye laser fluorescence system is shown to provide tunable, polarized, subnanosecond pulses at high repetition rates, modest peak powers, and low energy. Such a source is uniquely suited to fluorescence investigations of biochemical mechanisms. Applications of this fluorescence excitation source to analysis, life-time determination, and depolarization effects are discussed.     

In vitro anti-HIV activity of phosphorothioate alpha-anomeric oligodeoxynucleotides

Oligonucleotide analogs consisting exclusively of alpha-anomeric deoxynucleoside units bridged with phosphorothioate linkages have been synthesized and tested in vitro as antiviral agents against human immunodeficiency virus (HIV) in human T cells. Two 28-mers, an homopolymer alpha-S-dC28 and an oligomer alpha-S-anti-rev complementary to the initiation site of the regulatory viral gene rev exhibited antiviral activities comparable to those reported for the corresponding beta-anomeric phosphorothioate analogs. In contrast, a nuclease-resistant homopolymer, alpha-dC28 was inactive. Their preliminary results would indicate that the origin of oligonucleotide phosphorothioate anti-HIV activity is not exclusively correlated with their higher nuclease resistance.     

Effets de la consanguinité sur des caractères morphologiques quantitatifs chez Culex pipiens autogenicus Roub.

The influence of inbreeding on several morphological characters as proboscis, wings, leg and palp segments was examined in strictly inbred lines of C. pipiens autogenicus, starting with females from a natural population. The results show the importance of ccological conditions, especially temperature, during larval development of the population. We report a progressive average size reduction from the second inbred generation. The length variability increases in practically all cases, depending on the degree of inbreeding, which is often more marked in certain organs. The symmetry regulation is strongly affected. We observe highly significant individual values in the highly inbred generations. The distribution values clearly mark a left/right disturbance. The progression of asymmetry as a function of the degree of inbreeding is more marked in certain organs in the two sexes. The results show the importance of the advantage of heterozygotes.     

Effect of desglycine-arginine vasopressin on the excitability of the command neurons of the defensive reflex in the edible snail

Perfusion of the snail (Helix lucorum L.) CNS with DG-AVP (concentration 10(-6) M) in the course of low frequency intracellular stimulation (2-4-minute interval) of the defensive reflex command neurons led to an increase in the excitability. It was expressed both in the reduction of the spike generation latency, in the increased number of spikes in response to fixed stimuli, and in the activation of pacemaker potentials. If DG-AVP was added to the medium during endoneuronal habituation, there was no increase in the excitability. It is supposed that modification of the neuronal excitability may be caused by the DG-AVP effect on the pacemaker mechanism.     

Drought resistance in pearl millet

The influence of wilting on the levels of free proline, soluble proteins, reducing sugars, starch and on the activities of nitrate reductase, invertase, amylase and pyrophosphatases have been studied in the leaf tissue of five cultivars of pearl millet at their vegetative stage under pot culture conditions. The metabolic changes could not be correlated with the yield behaviour of the cultivars under a drought condition in the field.