Cellular localization of cytochrome c 553 in the N2-fixing cyanobacterium Anabaena variabilis

The in situ location of the electron carrier protein cytochrome C ₅₅₃ (cyt c ₅₅₃) has been investigated in both vegetative cells and heterocysts of the cyanobacterium Anabaena variabilis ATCC 29413 using the antibody-gold technique, carried out as a post-ernbedding immunoelectron microscopy procedure. When using a rabbit polyclonal anti-cyt c ₅₅₃ specific antiserum an intense labelling, associated mainly with the cell periphery (cytoplasmic membrane and periplasmic area), was seen in both heterocysts and vegetative cells. The selective release of most of the cellular cyt c ₅₅₃ during a Tris-EDTA treatment confirms a periplasmic localization of this protein in A. variabilis. The results indicate that most of cyt c ₅₅₃ is located in the periplasmic space. The roles ascribed to this protein in both respiration and photosynthesis in cyanobacteria are discussed.Abbreviations Cyt c ₅₅₃ cytochrome c ₅₅₃ - PBS phosphate buffered saline (20 mM sodium phosphate, 0.9% NaCl, pH 7.4) - PMSF phenylmethylsulfonyl fluoride Recipient of a Research Fellowship of the Alexander von Humboldt Foundation (Bonn, FRG) for a leave to the University of Konstanz.     

Physiological profile of world-class high-altitude climbers

The functional characteristics of six world-class high-altitude mountaineers were assessed 2-12 mo after the last high-altitude climb. Each climber on one or several occasions had reached altitudes of 8,500 m or above without supplementary O2. Static and dynamic lung volumes and right and left echocardiographic measurements were found to be within normal limits of sedentary controls (SC). Muscle fiber distribution was 70% type I, 22% type IIa, and 7% type IIb. Mean muscle fiber cross-sectional area was significantly smaller than that of SC (-15%) and of long-distance runners (LDR, -51%). The number of capillaries per unit cross-sectional area was significantly greater than that of SC (+ 40%). Total mitochondrial volume was not significantly different from that of SC, but its subsarcolemmal component was equal to that of LDR. Average maximal O2 consumption was 60 +/- 6 ml X kg-1 X min-1, which is between the values of SC and LDR. Average maximal anaerobic power was 28 +/- 2.5 W X kg-1, which is equal to that of SC and 40% lower that that of competitive high jumpers. All subjects were characterized by resting hyperventilation both in normoxia and in moderate (inspired O2 partial pressure = 77 Torr) hypoxia resulting in higher oxyhemoglobin saturation levels in hypoxia. The ventilatory response to four tidal volumes of pure O2 was similar to that of SC. It is concluded that elite high-altitude climbers do not have physiological adaptations to high altitude that justify their unique performance.     

The IsTaR 1 serodeme of Trypanosoma brucei: development of a new serodeme

An extensive serodeme of sequentially-isolated antigenic variants of African trypanosomes has been produced from both syringe-passaged and cyclically-transmitted Trypanosoma brucei of the IsTaR 1 clone derived from EATRO 164. The majority of the antigenic variants were isolated from chronically-infected deer mice (Peromyscus leucopus). The pattern of parasitemias during the course of infections initiated with syringe-passaged trypanosomes differed from those initiated with cyclically-transmitted trypanosomes. Trypanosome populations from syringe-passaged (192) and cyclically-transmitted (31) clones were each amplified by growth in lethally-irradiated mice and cryopreserved for retrospective analysis. Five clones derived from a single deer mouse during the first 44 days of infection, and 2 clones derived from an acutely-infected rat were established from these amplified populations. Homogeneous populations were grown in lethally-irradiated rats and mice for antigenic analysis purification of variant-specific glycoprotein. Six of the 7 clones were distinct variants by immunological criteria using antisera derived from whole cells or purified surface glycoproteins. Two clones, one derived from the acutely-infected rat, and the other from the first parasitemia in a chronic infection that was initiated with the former clone, were immunologically identical. Production of these clones established a well-defined serodeme that will allow detailed analysis of antigenic variation.     

Trypanosome hybrids generated in tsetse flies by nuclear fusion.

Genetic exchange may occur between two particular Trypanosoma brucei clones simultaneously transmitted by the same tsetse fly. We report here that this exchange takes place in the fly, through nuclear fusion. The resulting hybrids appear to be sub-tetraploid, some particular DNA sequences from one of the parental stocks being lost before enough cloned hybrid trypanosomes could be harvested for DNA analysis. A further reduction of the DNA content of these hybrids occurs gradually upon growth and yields near diploid value in a major part of the population. This mode of hybrid generation is different from the fusion of haploid gametes, which is thought to occur normally upon inoculation of metacyclic trypanosomes in their mammalian host. In this respect, the sub-tetraploid hybrids appear to undergo meiosis in the fly, generating sub-diploid metacyclic forms, then fusion in the mammalian blood.     

Effect of parasympathetic denervation on acetylcholine levels in the rat parotid gland. Is there an extraneuronal pool of acetylcholine?

Parasympathetic denervation of the rat parotid gland by avulsion of the auriculotemporal nerve caused a marked and lasting decrease in gland weight. Parasympathectomy did not change the levels of choline in the gland but decreased by 60% the levels of acetylcholine (ACh) ten days after surgery and 65% at 28 days. It is puzzling that relatively high levels of ACh remained after parasympathetic denervation. The presence of additional cholinergic nerves that innervate the gland, or pass through it en route to other structures may account for some of the remaining ACh. Also, Schwann cells from denervated nerves might have contributed to some of the ACh. The existence of an extraneuronal source of ACh is considered.     

Struttura ed ultrastruttura dell'apparato genitale maschile di Drosophila melanogaster Meig.

Summary The structure of the testes of Drosophila melanogaster Meig. was re-examined by means of phase contrast and polarized light microscopy; the ultrastructure was investigated by electron microscopy. Testes from adult virgins of wild strain Varese were studied, but some observations were made also on the testes of different aged insects, of some insects examined at different times during and after mating, and on testes from sterile mutant strains.The results are summarized in the following points: 1) The testis is made up of an external wall and of an internal germinal tissue. The wall appears to be composed of two overlapping layers of very flattened cells: pigmented cells and muscle cells. 2) The ultrastructure of the muscle cells gives rise to some interesting considerations arising out of the fact that there are two kinds of filaments, but without any evident transverse band organization. 3) The testis falls into three different portions according to the organisation of the germinal tissue: the apical portion (spermatogonial zone), the middle portion (spermagenetic zone) and the terminal portion (spermatic zone). 4) The germinal tissue is made up of germinal cells and interstitial cells. The germinal cells occur in groups consisting of a fixed number of elements in a syncytial state: these groups are enveloped by interstitial cells forming the cyst. The cysts can be considered as the supracellular unit of germinal tissue.The results are discussed in relation to numerous problems, such as: the existence and meaning of the syncytial state of the germinal cells; the existence of a functional cycle of the interstitial cells associated with the maturation of germinal elements; the phagocytic and mechanical functions of terminal epithelium; the existence of various movements of germinal tissue elements along the length of the testis from the apical zone to the terminal one.The paper ends with a discussion on functional aspects of the male reproductive organs.

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Ricerche eseguite col sussidio del C.N.R. (Roma).     

Identification of two different glyceraldehyde-3-phosphate dehydrogenases (phosphorylating) in the photosynthetic protist Cyanophora paradoxa

Two different glyceraldehyde-3-phosphate (G3P) dehydrogenase (phosphorylating) activities, namely NAD- and NADP-dependent, have been found in cell extracts of the cyanelle-bearing photosynthetic protist Cyanophora paradoxa. Whereas the two G3P dehydrogenase activities were detected with similar specific activity levels (0.1 to 0.2 U/mg of protein) in extracts of the photosynthetic organelles (cyanelles), only the NAD-dependent activity was found in the cytosol. Thus, a differential intracellular localization occurred. The perfect overlapping of the two G3P dehydrogenase activity peaks of the cyanelle in both hydrophobic interaction chromatography and subsequent FPLC (fast protein liquid chromatography) gel filtration indicated that the two activities were due in fact to a single NAD(P)-dependent G3P dehydrogenase (EC 1.2.1.-) with a molecular mass of 148,000. SDS-PAGE of active fractions from FPLC gel filtration showed that the intensity of the major protein band (molecular mass, 38,000) of the enzyme preparation clearly paralleled the activity elution profile, thus suggesting a tetrameric structure for the cyanelle dehydrogenase. On the other hand, FPLC gel filtration analysis of the cytoplasmic fraction revealed a NAD-dependent G3P dehydrogenase with a native molecular mass of 142,000, being equivalent to the classical glycolytic enzyme (EC 1.2.1.12) present in the cytosol of all the organisms so far studied. The significance of these results is discussed taking into account that the cyanobacteria, photosynthetic prokaryotes which share many structural and biochemical features with cyanelles and are considered as their ancestors, have a similar NAD(P)-dependent G3P dehydrogenase.Abbreviation FPLC Fast protein liquid chromatography     

Diversity of Xiphinema americanum-group Species and Hierarchical Cluster Analysis of Morphometrics

Of the 39 species composing the Xiphinema americanum group, 14 were described originally from North America and two others have been reported from this region. Many species are very similar morphologically and can be distinguished only by a difficult comparison of various combinations of some morphometric characters. Study of morphometrics of 49 populations, including the type populations of the 39 species attributed to this group, by principal component analysis and hierarchical cluster analysis placed the populations into five subgroups, proposed here as the X. brevicolle subgroup (seven species), the X. americanum subgroup (17 species), the X. taylori subgroup (two species), the X. pachtaicum subgroup (eight species), and the X. lambertii subgroup (five species).     

Occupancy versus colonization–extinction models for projecting population trends at different spatial scales

Understanding spatiotemporal population trends and their drivers is a key aim in population ecology. We further need to be able to predict how the dynamics and sizes of populations are affected in the long term by changing landscapes and climate. However, predictions of future population trends are sensitive to a range of modeling assumptions. Deadwood‐dependent fungi are an excellent system for testing the performance of different predictive models of sessile species as these species have different rarity and spatial population dynamics, the populations are structured at different spatial scales, and they utilize distinct substrates. We tested how the projected large‐scale occupancies of species with differing landscape‐scale occupancies are affected over the coming century by different modeling assumptions. We compared projections based on occupancy models against colonization–extinction models, conducting the modeling at alternative spatial scales and using fine‐ or coarse‐resolution deadwood data. We also tested effects of key explanatory variables on species occurrence and colonization–extinction dynamics. The hierarchical Bayesian models applied were fitted to an extensive repeated survey of deadwood and fungi at 174 patches. We projected higher occurrence probabilities and more positive trends using the occupancy models compared to the colonization–extinction models, with greater difference for the species with lower occupancy, colonization rate, and colonization:extinction ratio than for the species with higher estimates of these statistics. The magnitude of future increase in occupancy depended strongly on the spatial modeling scale and resource resolution. We encourage using colonization–extinction models over occupancy models, modeling the process at the finest resource‐unit resolution that is utilizable by the species, and conducting projections for the same spatial scale and resource resolution at which the model fitting is conducted. Further, the models applied should include key variables driving the metapopulation dynamics, such as the availability of suitable resource units, habitat quality, and spatial connectivity.     

Introduction to Special Section: Understanding Paths to Youth Purpose—Why Content and Contexts Matter

Applying latent class and regression techniques to data from the NICHD Study of Early Child Care and Youth Development (n = 997), this study explored the potential academic advantages of time spent in out-of-school activities. Of particular interest was how these potential advantages played out in relation to the timing and duration of activity participation and the family contexts in which it occurred. Participation closer to the start of high school—including consistent participants and latecomers—was associated with higher grades at the transition into high school, especially for youth from low-income families. Sensitivity analyses indicated that this link between school-age activity participation and adolescent academic progress was unlikely to be solely a function of selection. It also tended to be more pronounced among youth from lower-income families, although without varying by other aspects of family status or process.