4-Amino-6-methylhept-2-enoic acid: a leucine analogue and potential probe for localizing sites of proteolytic control in the hepatocyte.

A recent analysis of leucine analogues has suggested that the carboxyl group is not required for mediating low concentration proteolytic inhibition in liver cells. In designing a probe to localize the regulatory site(s), we tested this hypothesis by synthesizing an analogue with a 2-carbon insert between the carboxyl and alpha-carbon. The Wittig product, a trans olefin, was fully active. Surprisingly, low concentration activity was lost when the double bond was eliminated by hydrogenation although some inhibitory effectiveness at high concentrations was evident. Since the double bond extends the carboxyl group away from the alpha-carbon, the results support the above hypothesis as well as the feasibility of adding functional groups to the carboxyl end of leucine.     

Annual breeding in a captive smalltooth sawfish,Pristis pectinata

The critically endangered smalltooth sawfish Pristis pectinata reproduces biennially in central west Florida, U.S.A. Here we demonstrate that smalltooth sawfish are physiologically capable of reproducing annually in a captive environment. The smalltooth sawfish are held in an open system, with abiotic conditions that vary naturally with the surrounding environment in The Bahamas. This suggests wild smalltooth sawfish may also be capable of annual reproduction provided there are adequate prey resources, limited competition and mate availability.     

Bio-stretch, a computerized cell strain apparatus for three-dimensional organotypic cultures

Summary In the present study, a unique mechanical strain apparatus for three-dimensional organotypic cultures was developed into a computerized system. It consists of a personal computer running Windows-based software, the Bio-Stretch Manager, a Bio-Stretch Controller, and three sets of magnet boards. Cells are cultured on a Gelfoam? sponge that is placed in a 35-mm petri dish with one end glued to the dish, and the other end attached to a coated steel bar. The petri dish is placed in front of a magnet, and the movement of the steel bar is controlled by dynamically changing the magnetic field. Up to five stretch patterns of variable frequency, duty cycle, and magnitude can be designed for each stretch regimen. Three different stretch regimens can be tested simultaneously. The operational characteristics of sponges were examined. Attachment of cells to the sponges was observed on several cell types. These features provide wide options for using this system to study the effects of mechanical stretch on cells.     

Phylogeny and systematics of the bee genus Osmia (Hymenoptera: Megachilidae) with emphasis on North American Melanosmia: subgenera,synonymies and nesting biology revisited

The predominantly Holarctic bee genus Osmia Panzer is species‐rich and behaviourally diverse. A robust phylogeny of this genus is important for understanding the evolution of the immense variety of morphological and behavioural traits exhibited by this group. We infer a phylogeny of Osmia using DNA sequence data obtained from three nuclear genes (elongation factor 1‐α, LW‐rhodopsin and CAD) and the mitochondrial gene COI. Our taxon sampling places special attention on North American members of the subgenus Melanosmia Schmiedeknecht; we discuss the novel placement of a number of species traditionally assigned to O. (Melanosmia) and examine the relative support for alternative classifications of this species‐rich subgenus. We use this new phylogeny to guide a reassessment of morphological and behavioural characters within Osmia. Our results provide support for the recognition of Osmia (Hapsidosmia), subgen.n ., a monotypic subgenus containing Osmia iridis Cockerell & Titus. We synonymize Osmia (Mystacosmia) Snelling under O. (Melanosmia), syn.n . We synonymize Osmia (Acanthosmioides) Ashmead under O. (Melanosmia), syn.n ., propose ‘odontogaster species group’ as a replacement for the subgeneric name Acanthosmioides, and refine the morphological characters that serve to diagnose the species group. We additionally propose ‘nigrifrons species group’ for a clade within O. (Melanosmia) containing most species formerly placed in Osmia (Centrosmia) Robertson. We demonstrate more cohesive patterns of nest substrate use in the nigrifrons and odontogaster species groups than was previously believed to occur, reconsider character polarity of aspects of the female mandible, and show that a large number of morphological characters have evolved convergently within the genus. In order to facilitate discussion of relevant taxa, we propose the following 15 new synonymies: O. bakeri Sandhouse under O. melanopleura Cockerell; O. crenulaticornis Michener under O. pinorum Cockerell; O. claremontensis Michener under O. sedula Sandhouse; O. cockerelli Sandhouse under O. dakotensis Michener; O. francisconis White under O. enixa Sandhouse; O. hurdi White under O. austromaritima Michener; O. sladeni Sandhouse under O. nifoata Cockerell; O. titusi Cockerell under O. phenax Cockerell; O. subtrevoris Cockerell, O. physariae Cockerell, and O. erecta Michener under O. giliarum Cockerell; and O. universitatis Cockerell, O. integrella Cockerell, O. amala Cockerell, and O. metitia Cockerell under O. nigrifrons Cresson, syn.n . We remove O. wyomingensis Michener from synonymy with O. nifoata Cockerell, stat.n ., and O. pinorum Cockerell from synonymy with O. physariae Cockerell, stat.n . This published work has been registered in ZooBank, http://zoobank.org/urn:lsid:zoobank.org:pub:A3E7D63B‐5C4C‐4ACF‐BF33‐48E5C5DD1B0D .     

Rapid Induction of Ion Pulses in Tomato,Cucumber, and Maize Plants following a Foliar Application of L(+)-Adenosine

Application of picomole quantities of (+)-adenosine, a plant growth-regulating second messenger elicited by triacontanol, to tomato (Lycopersicon esculentum Mill.), maize (Zea mays L.), and cucumber (Cucumis sativa L.) foliage, increased Ca2+, Mg2+, and K+ concentrations in the exudate from the stumps of excised plants by 20 to 60% within 5 s after treatment. The change in ionic concentration of the exudate was transitory. When L(+)-adenosine and triacontanol were applied to different tomato plants at the same time, the L(+)-adenosine caused an increase in Ca2+ flux within 3 s, whereas a significant increase from triacontanol was not detectable until 5 min after application. This was expected because triacontanol elicits the formation of L(+)-adenosine. The enantiomer of L(+)-adenosine, D(-)-adenosine, had no effect on the cation concentration in tomato and inhibited the effect of L(+)-adenosine at equimolar or lower concentrations. These observations suggest that L(+)-adenosine acts by eliciting a rapidly propagated signal that increases the concentration of several ions in the apoplast. We postulate that modulations in apoplastic ion concentration, especially increases in Ca2+ concentration, constitute a mechanism by which plants regulate metabolic activity and growth in response to certain stimuli.     

Endogenous chloride channels of insect sf9 cells. Evidence for coordinated activity of small elementary channel units

The endogenous Cl- conductance of Spodoptera frugiperda (Sf9) cells was studied 20-35 h after plating out of either uninfected cells or cells infected by a baculovirus vector carrying the cloned beta-galactosidase gene (beta-Gal cells). With the cation Tris+ in the pipette and Na+ in the bath, the reversal potential of whole-cell currents was governed by the prevailing Cl- equilibrium potential and could be fitted by the Goldman-Hodgkin-Katz equation with similar permeabilities for uninfected and beta-Gal cells. In the frequency range 0.12 < f < 300 Hz, the power density spectrum of whole-cell Cl- currents could be fitted by three Lorentzians. Independent of membrane potential, >50% of the total variance of whole-cell current fluctuations was accounted for by the low frequency Lorentzian (fc = 0.40 +/- 0.03 Hz, n = 6). Single-Cl- channels showed complex gating kinetics with long lasting (seconds) openings interrupted by similar long closures. In the open state, channels exhibited fast burst-like closures. Since the patches normally contained more than a single channel, it was not possible to measure open and closed dwell-time distributions for comparing single-Cl- channel activity with the kinetic features of whole-cell currents. However, the power density spectrum of Cl- currents of cell-attached and excised outside-out patches contained both high and low frequency Lorentzian components, with the corner frequency of the slow component (fc = 0.40 +/- 0.02 Hz, n = 4) similar to that of whole-cell current fluctuations. Chloride channels exhibited multiple conductance states with similar Goldman-Hodgkin-Katz-type rectification. Single-channel permeabilities covered the range from approximately 0.6.10(-14) cm5/s to approximately 6.10(-14) cm3/s, corresponding to a limiting conductance (gamma 150/150) of approximately 3.5 pS and approximately 35 pS, respectively. All states reversed near the same membrane potential, and they exhibited similar halide ion selectivity, P1 > PCl approximately PBr. Accordingly, Cl- current amplitudes larger than current flow through the smallest channel unit resolved seem to result from simultaneous open/shut events of two or more channel units.     

Electrofusion and electroporation of plants

The utilization of electrofusion and electroporation techniques has had a major impact on the genetic manipulation of plants within the last decade. This review of the development of electrofusion and electroporation, as it applies to plants, highlights major developmental aspects of this technology. These include mechanisms for cell fusion, molecular exchange, and parameters that affect the efficiency of fusion and electroporation.     

9-β-L(+) Adenosine: A new naturally occurring plant growth substance elicited by triacontanol in rice

The naturally occurring plant growth substance elicited by triacontanol was found to be 9--L(+) adenosine by physical and spectral methods. At picomolar concentrations, 9--L(+) adenosine stimulated growth as determined by dry weight measurements of several plant species. Reaction of adenosine deaminase with adenosine from rice showed that small quantities of 9--L(+) adenosine exist in plants. We believe this is the first report of 9--L(+) adenosine as a natural product.     

Electrical and adaptive properties of rod photoreceptors in bufo marinus. I. Effects of altered extracellular Ca(2+) levels

The effects of altering extracellular Ca(2+) levels on the electrical and adaptive properties of toad rods have been examined. The retina was continually superfused in control (1.6 mM Ca(2+)) or test ringer’s solutions, and rod electrical activity was recorded intracellularly. Low-calcium ringer’s (10(-9)M Ca(2+)) superfused for up to 6 min caused a substantial depolarization of the resting membrane potential, an increase in light-evoked response amplitudes, and a change in the waveform of the light-evoked responses. High Ca(2+) ringer’s (3.2 mM) hyperpolarized the cell membrane and decreased response amplitudes. However, under conditions of either low or high Ca(2+) superfusion for up to 6 min, in both dark-adapted and partially light-adapted states, receptor sensitivity was virtually unaffected; i.e., the V-log I curve for the receptor potential was always located on the intensity scale at a position predicted by the prevailing light level, not by Ca(2+) concentration. Thus, we speculate that cytosol Ca(2+) concentration is capable of regulating membrane potential levels and light-evoked response amplitudes, but not the major component of rod sensitivity. Low Ca(2+) ringer’s also shortened the period of receptor response saturation after a bright but nonbleaching light flash, hence accelerating the onset of both membrane potential and sensitivity recovery during dark adaptation.

Exposure of the retina to low Ca(2+) (10(-9)M) ringer’s for long periods (7-15 min) caused dark-adapted rods to lose responsiveness. Response amplitudes gradually decreased, and the rods became desensitized. These severe conditions of low Ca(2+) caused changes in the dark-adapted rod that mimic those observed in rods during light adaptation. We suggest that loss of receptor sensitivity during prolonged exposure to low Ca(2+) ringer’s results from a decrease of intracellular (intradisk) stores of Ca(2+); i.e., less Ca(2+) is thereby released per quantum catch.