Calcium-dependent anion channel in the water mold,Blastocladiella emersonii

Summary Injection of depolarizing current into vegetative cells of the water moldBlastocladiella emersonii elicits a regenerative response that has the electrical characteristics of an action potential. Once they have been taken past a threshold of about –40 mV, cells abruptly depolarize to +20 mV or above; after an interval ranging from several hundred milliseconds to a few seconds, the cells spontaneously return to their resting potential near –100 mV. When the action potential was analyzed with voltage-clamp recording, it proved to be biphasic. The initial phase reflects an influx of calcium ions through voltage-sensitive channels that also carry Sr²⁺ ions. The delayed, and more extended, phase of inward current results from the efflux of chloride and other anions. The anion channels are broadly selective, passing chloride, nitrate, phosphate, acetate, succinate and even PIPES. The anion channels open in response to the entry of calcium ions, but do not recognize Sr²⁺. Calcium channels, anion channels and calcium-specific receptors that link the two channels appear to form an ensemble whose physiological function is not known. Action potentials rarely occur spontaneously but can be elicited by osmotic downshock, suggesting that the ion channels may be involved in the regulation of turgor.     

Evidence for titratable gating charges controlling the voltage dependence of the outer mitochondrial membrane channel,VDAC

Summary A voltage-dependent anion-selective channel, VDAC, is found in outer mitochondrial membranes. VDAC's conductance is known to decrease as the transmembrane voltage is increased in either the positive or negative direction. Charged groups on the channel may be responsible for this voltage dependence by allowing the channel to respond to an applied electric field. If so, then neutralization of these charges would eliminate the voltage dependence. Channels in planar lipid bilayers which behaved normally at pH 6 lost much of their voltage dependence at high pH. Raising the pH reduced the steepness of the voltage dependence and raised the voltage needed to close half the channels. In contrast, the energy difference between the open and closed state in the absence of a field was changed very little by the elevated pH. The groups being titrated had an apparent pK of 10.6. From the pK and chemical modification, lysine epsilon amino groups are the most likely candidates responsible for VDAC's ability to respond to an applied electric field.     

Transposon donor plasmids, based on ColIb-P9, for use in Pseudomonas putida and a variety of other gram negative bacteria

Summary The properties of pLG221, a derivative of the ColIb plasmid carrying the transposon Tn5 are described. This plasmid can be used to introduce Tn5 by conjugation from Escherichia coli into a variety of Gram negative bacteria outside the host range for maintenance of ColIb. Plasmid pLG221, and a similar plasmid pLG223 carrying Tn10 may be of general utility as vectors for transposon-mediated mutagenesis in a variety of Gram negative bacteria.     

Frequencies of simultaneous transformation with different T-DNAs and their relevance to the Agrobacterium/plant cell interaction

Summary We investigated whether the efficiency of transformation of plant cells by Agrobacterium tumefaciens during cocultivation is limited by the properties of the plant cells or by the infecting bacteria.Therefore, tobacco protoplasts were infected by cocultivation with two different agrobacteria strains carrying Ti plasmids with distinguishable T-DNAs. These T-DNAs cotransform plant cells at a frequency equal to the product of their independent transformation frequencies, which indicates that all plant cells are equally competent. On the other hand, when these T-DNAs are located on the same Ti plasmid vector within one bacterial strain, the cotransformation frequency is significantly higher than the product of the single transformation frequencies. We interpret these results to indicate that transformation is limited more by the establishment of effective bacteria/plant cell interaction than by (i) the process of DNA integration and (ii) by the number of plant cells capable of being transformed by Agrobacterium. We found that most plant cells are transformed by only one or a few agrobacteria. Analysis of the number of T-DNA copies in these clonally transformed lines indicates amplification of the original, infecting T-region copy.     

Techniques for studying the execution of foreign queens by temporal subcastes in fire ants (Solenopsis invicta)

Using monogynous and polygynous colonies of the fire ant, Solenopsis invicta Buren, we developed methodology to determine which behavioural subcaste of workers was responsible for executing unfamiliar queens that were introduced to them. Separation of subcastes and introduction of queens to each of these separately was partly effective, but more accurate results were obtained by removing workers that were in the act of executing queens, marking them individually, and returning them to the colony. Their subsequent behaviour was then recorded to determine whether they behaved like nurses, reserves, or foragers. The results showed that foragers are dominant in execution behaviour and that all morphological subcastes (minors, medias, and majors) are involved. This methodology may be applied to other social insect species.

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Résumé A l'aide de colonies monogynes de S. invicta Buren, nous avons testé la sensibilité de deux méthodes: Premièrement, nous avons isolé les trois sous-castes temporelles des ouvrières (nurses, réserves et fourrageuses) auxquelles nous avons introduit des reines étrangères. Nous avons trouvé que les fourrageuses étaient le groupe le plus agressif, exécutant un pourcentage élevé des reines qui leur étaient présentées. Le degré de physogastrie de la reine étrangère, sa colonie d'origine et la présence de couvain n'avaient pas d'effet visible sur sa destinée. La sensibilité de cette méthode était limitée par la difficulté d'une séparation complète des souscastes temporelles.Deuxièmement, nous avons capturé des ouvrières exécutant activement des reines étrangères, après marquage nous les avons remises dans leur colonie pour observations ultérieures. Nous avons remarqué que leur localisation dans le nid et leur comportement correspondaient aux séquences trouvées pour les fourrageuses bien plus qu'à celles des ouvrières réserves ou nurses. Cette méthode est plus sensible. Des mesures de la largeur de la capsule céphalique de ces ouvrières ont montré qu'aucune des sous-caste morphologiques (mineurs, moyennes et majeurs) étaient dominantes dans le comportement d'exécution. Nos résultats indiquent que la sensibilité des ouvrières à certaines phéromones de la reine et odeur de la colonie augmente avec leur âge.

     

The regulation of''early'' enzymes during the development and dedifferentiation of Dictyostelium discoideum

The specific activities of the enzymes alpha-mannosidase and N-acetylglucosaminidase increase immediately after the initiation of the development of bacterially grown cell cultures of Dictyostelium discoideum. The regulation of these two enzymes was found to be dissociable in the developmental timer mutant, FM-1, which aggregates 4.5 h earlier than wild-type cells due to the absence of the first rate-limiting component of the preaggregative period. The increase in alpha-mannosidase activity occurs in the absence of the first rate-limiting component, but the increase in N-acetylglucosaminidase activity does not. These results indicate the following: (1) the increase in the specific activity of alpha-mannosidase is not related to the timing of subsequent developmental stages; (2) the increase in the specific activity of N-acetylglucosaminidase is not necessary for the subsequent developmental program; and (3) either the increase in the specific activity of N-acetylglucosaminidase is dependent upon progress through the first rate-limiting component, or the increase in this enzyme activity and the first rate-limiting component are both dependent upon an early event for which FM-1 is defective. In addition to early development, we monitored the two enzyme activities during dedifferentiation. The results demonstrate that there is no difference between dedifferentiating wild-type cells and dedifferentiation-defective mutant HI-4 cells. Changes in enzyme specific activity accompanying dedifferentiation are dependent upon the composition of the dedifferentiation-inducing media and are consistent with the levels of these enzymes observed in cells growing in the different nutrient media.     

Enzyme kinetics of a highly purified mitochondrial creatine kinase in comparison with cytosolic forms

Summary Mitochondrial creatine kinase (CK) purified from canine myocardium showed a single protein band on SDS-PAGE and was free of MMCK. Its amino acid composition was different than MMCK or BBCK and did not react to antiserum to MMCK or BBCK. Using purified mitochondrial, MM and BBCK, the velocity of reaction (V) was estimated for creatine phosphate (CP), creatine (C), adenosine triphosphate (ATP) and adenosine diphosphate (ADP) over a wide range of concentrations including those at V_max. The values for K_m (mM/L) derived from Lineweaver-Burke plots are shown: The affinity of mitochondrial CK for C is much greater than MMCK which is compatible with the energy shuttle hypothesis, namely ATP is converted by mitochondrial CK to CP, and then diffuses to the myofibril for conversion to ATP for utilization.     

Analysis of sister chromatid exchanges in lymphocytes cultured from 71 healthy men

Sister chromatid exchanges (SCE) were analyzed in peripheral blood lymphocytes from a select group of 71 healthy men, 56 nonsmokers and 15 cigarette smokers. In addition to estimating baseline SCE, data were examined to seek relationships of SCE frequencies to age and smoking. The baseline value of 7.53 SCE per cell from the 56 nonsmokers was within the range (5.60 to 9.10 SCE/cell) reported for other human populations. No relationship was found between the mean SCE frequency per cell and age. However, a significant increase in the SCE mean value was observed in smokers as compared to nonsmokers. The results of this study are compared with those of other reports on SCE effects of age and smoking.Abbreviations BUdR 5-bromo,2-deoxyuridine - SCE sister chromatid exchange     

Thermoregulation and metabolism in the smallest African gerbil, Gerbillus pusillus

The effect of temperature on thermoregulation, metabolism, evaporative water loss and thermal conductance was studied in Gerbillus pusillus . Its resting body temperature (TB) was 34·6°C, approximately 5°C higher than the mean ambient temperature (TA) encountered in its burrow. As TA increased above 34°C, its ability to lose heat to the environment decreased. It overcame this problem by tolerating increases in TB to a non-lethal maximum of 41°C, whilst also eliminating increasing quantities of obligate heat by pulmocutaneous evaporation and conduction.
Metabolic rate was 41% lower than that predicted from Kleiber's (1975) allometric equation. This confers a considerable saving in energy in an environment where food is often scarce, whilst simultaneously reducing heat production and the degree of gaseous exchange in the already oxygen-poor and carbon dioxide-rich environment encountered in the plugged burrows of its natural milieu.
Gerbillus pusillus , therefore, does not maintain strict homeothermy and utilizes a labile TB and reduced metabolic rate as an adaptive mechanism for survival in the arid zones of tropical Africa.     

Predation at a snail's pace: what's time to a gastropod?

Summary Predation by naticid gastropods shows evidence of adaptation to maximize the rate of energy intake. The predation rate of Polinices duplicatus feeding on artificially altered, thin-shelled Mercenaria mercenaria was faster than the predation rate on normal Mercenaria. The rate of energy intake was limited by handling time. The time saved by predation on thin-shelled prey was used to forage. Thus time was shown to be valuable to P. duplicatus, and cost-benefit functions using time and energy as currencies are appropriate for estimating dietary efficiency and predicting prey choice.Despite the clear superiority of thin-shelled prey, P. duplicatus did not learn to prefer this novel prey type, suggesting that predator choices are sterotyped, reflecting optima selected over evolutionary time.