Trimethyloxonium modification of single batrachotoxin-activated sodium channels in planar bilayers. Changes in unit conductance and in block by saxitoxin and calcium

Single batrachotoxin-activated sodium channels from rat brain were modified by trimethyloxonium (TMO) after incorporation in planar lipid bilayers. TMO modification eliminated saxitoxin (STX) sensitivity, reduced the single channel conductance by 37%, and reduced calcium block of inward sodium currents. These effects always occurred concomitantly, in an all-or-none fashion. Calcium and STX protected sodium channels from TMO modification with potencies similar to their affinities for block. Calcium inhibited STX binding to rat brain membrane vesicles and relieved toxin block of channels in bilayers, apparently by competing with STX for the toxin binding site. These results suggest that toxins, permeant cations, and blocking cations can interact with a common site on the sodium channel near the extracellular surface. It is likely that permeant cations transiently bind to this superficial site, as the first of several steps in passing inward through the channel.     

Light-activated proton-motive force generation in lipid vesicles containing cytochrome b-c1 complex and bacterial reaction centres

(1) Purified bovine heart mitochondrial cytochrome b-c1 complex (ubiquinone-cytochrome c oxidoreductase) and photosynthetic reaction centres isolated from Rhodopseudomonas sphaeroides strain R-26 have been incorporated into lipid vesicles. In the presence of cytochrome c and ubiquinone-2, light activation caused a cyclic electron transfer involving both components. (2) Since cytochrome c is added outside the vesicles, it is both reduced by the cytochrome b-c1 complex and oxidised by the reaction centre on the outside of the vesicles. Ubiquinone-2, however, is reduced by the reaction centres at a site in contact with the inside of the vesicles, but the reduced form, ubiquinol-2, is oxidised by the cytochrome b-c1 complex at a site in contact with the outer aqueous phase. (3) In the presence of valinomycin plus K+, initiation of cyclic electron flow causes protons to move from inside the vesicles to the outer medium and the H +/2e- ratio was calculated to be close to 4.     

The suitability of some plant hosts for the development of the peach-potato aphid, Myzus persicae (Sulzer)

Myzus persicae develop well on Brassica species, particularly those that grow rapidly, such as mustard and turnip, but much less well on sugar beet, spinach and lettuce. They usually develop better on young, rapidly growing leaves than on mature leaves. Two clones of M. persicae behaved similarly on the host plants tested.

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Zusammenfassung Die Entwicklung von Myzus persicae-Alienicolen auf den Sekundärwirten Kohlrüben, Kopfkohl, Chinakohl, Brokkoli, Blumenkohl, Senf, Raps, Grünkohl sowie Zuckerrübe, Spinat und Salat wurde durch wiederholte Erfassung der durchschnittlichen und totalen Larvenproducktion einzelner Jungfern sowie ihrer Mortalität in Gewächshausversuchen verfolgt und mit Auszählung des Befalls von Freilandpflanzen verglichen. Myzus persicae entwickelte sich gut an Brassica-Arten, besonders an raschwüchsigen wie Senf und Kohlrüben, aber viel weniger gut an Zuckerrübe, Spinat and Salat. Sie entwickelt sich gewöhnlich an jungen schnell wachsenden Blättern besser als an ausgereiften. Zwei Klone von Myzus persicae verhielten sich an den geprüften Wirtspflanzen ähnlich.

     

Relative apparent synapomorphy analysis (RASA). I: The statistical measurement of phylogenetic signal

We have developed a new approach to the measurement of phylogenetic signal in character state matrices called relative apparent synapomorphy analysis (RASA). RASA provides a deterministic, statistical measure of natural cladistic hierarchy (phylogenetic signal) in character state matrices. The method works by determining whether a measure of the rate of increase of cladistic similarity among pairs of taxa as a function of phenetic similarity is greater than a null equiprobable rate of increase. Our investigation of the utility and limitations of RASA using simulated and bacteriophage T7 data sets indicates that the method has numerous advantages over existing measures of signal. A first advantage is computational efficiency. A second advantage is that RASA employs known methods of statistical inference, providing measurable sensitivity and power. The performance of RASA is examined under various conditions of branching evolution as the number of characters, character states per character, and mutations per branch length are varied. RASA appears to provide an unbiased and reliable measure of phylogenetic signal, and the general approach promises to be useful in the development of new techniques that should increase the rigor and reliability of phylogenetic estimates.      

Gravitropically-stimulated seedlings show autotropism in weightlessness

In a spaceflight experiment, autotropism by oat ( Avena sativa L.) coleoptiles following gravitropic responses was prominent in weightlessness: counter-reactions led to the straightening of the curved coleoptiles. This was not the case during clinorotation on earth. The autotropic reactions appeared to be related to the stimulus received during the stimulus period, i.e. the greater the response the greater the autotropic counter-reaction. Previous models of the gravitropic system which predicted that coleoptiles would not straighten in weightlessness are disproved. A modification to one of the models is proposed which includes the autotropic response observed in spaceflight. The nature of the counter-reactions in the absence of gravitropic stimulation is discussed.     

Variation in heat-shock proteins among species of desert fishes (Poeciliidae, Poeciliopsis)

Analysis of the heat-shock proteins (hsps) of six closely related species of Poeciliopsis demonstrated the existence of biochemical diversity in the hsp100, hsp70, hsp60, and hsp30 protein families among species. Each species expressed five to seven hsp70-related isoforms. Constitutive 70-kD isoforms were identical among species, but four different patterns of heat-inducible isoforms were seen in these six species. Members of the hsp70 family of molecular chaperones are included among the most highly conserved proteins known, and the possibility of variation in hsp70 among closely related species has rarely been addressed. The hsp30 family is known to be less conserved than the hsp70 family, and, as expected, the Poeciliopsis hsp30 patterns showed more variation. Most of the hsp30 isoforms characteristic of a particular species were unique to that species. Hsp100 and hsp60 were identical in five of the species, but alternate isoforms were found in P. monacha. The small size and limited geographical distribution of the P. monacha population have probably contributed to the uniqueness of the monacha pattern. Two of the species were shown to acquire thermotolerance, the ability to withstand normally lethal temperatures when subjected to a gradual temperature increase. Rapid-heating protocols commonly used to establish critical thermal maxima of organisms do not include this inducible component of thermoresistance and therefore do not adequately assess an organism's capacity to withstand thermal stress.      

Variation in heat shock proteins within tropical and desert species of poeciliid fishes

The 70-kilodalton heat shock protein (hsp70) family of molecular chaperones, which contains both stress-inducible and normally abundant constitutive members, is highly conserved across distantly related taxa. Analysis of this protein family in individuals from an outbred population of tropical topminnows, Poeciliopsis gracilis, showed that while constitutive hsp70 family members showed no variation in protein isoforms, inducibly synthesized hsp70 was polymorphic. Several species of Poeciliopsis adapted to desert environments exhibited lower levels of inducible hsp70 polymorphism than the tropical species, but constitutive forms were identical to those in P. gracilis, as they were in the confamilial species Gambusia affinis. These differences suggest that inducible and constitutive members of this family are under different evolutionary constraints and may indicate differences in their function within the cell. Also, northern desert species of Poeciliopsis synthesize a subset of the inducible hsp70 isoforms seen in tropical species. This distribution supports the theory that ancestral tropical fish migrated northward and colonized desert streams; the subsequent decrease in variation of inducible hsp70 may have been due to genetic drift or a consequence of adaptation to the desert environment. Higher levels of variability were found when the 30- kilodalton heat shock protein (hsp30) family was analyzed within different strains of two desert species of Poeciliopsis and also in wild-caught individuals of Gambusia affinis. In both cases the distribution of hsp30 isoform diversity was similar to that seen previously with allozyme polymorphisms.