Protistan microbial observatory in the Cariaco Basin,Caribbean. I. Pyrosequencing vs Sanger insights into species richness

Microbial diversity and distribution are topics of intensive research. In two companion papers in this issue, we describe the results of the Cariaco Microbial Observatory (Caribbean Sea, Venezuela). The Basin contains the largest body of marine anoxic water, and presents an opportunity to study protistan communities across biogeochemical gradients. In the first paper, we survey 18S ribosomal RNA (rRNA) gene sequence diversity using both Sanger- and pyrosequencing-based approaches, employing multiple PCR primers, and state-of-the-art statistical analyses to estimate microbial richness missed by the survey. Sampling the Basin at three stations, in two seasons, and at four depths with distinct biogeochemical regimes, we obtained the largest, and arguably the least biased collection of over 6000 nearly full-length protistan rRNA gene sequences from a given oceanographic regime to date, and over 80 000 pyrosequencing tags. These represent all major and many minor protistan taxa, at frequencies globally similar between the two sequence collections. This large data set provided, via the recently developed parametric modeling, the first statistically sound prediction of the total size of protistan richness in a large and varied environment, such as the Cariaco Basin: over 36 000 species, defined as almost full-length 18S rRNA gene sequence clusters sharing over 99% sequence homology. This richness is a small fraction of the grand total of known protists (over 100 000–500 000 species), suggesting a degree of protistan endemism.     

Multiline varieties and disease control

Summary A general model for the evolution of pathogen populations on mixtures or multilines is developed. This model is used to extend previous analyses of the effects of the widespread cultivation of multilines on the evolution of virulence in obligate parasites to mixtures of lines carrying different numbers of resistance genes. It is concluded that the composition of an equilibrium pathogen population growing on a multiline may vary within wide limits and the prinicipal determinant of its composition is the number of components in the multiline and the resistance genes they carry. Other factors of importance are (i) the relative contribution made by each host class (with different numbers of resistance genes) to the pathogen spore pool each generation; (ii) the levels of stabilizing selection against unnecessary virulence genes; and (iii) the way in which unnecessary genes for virulence combine to reduce pathogen fitness. Conditions for the fixation of avirulent biotypes in the pathogen population and the evolution of a pathogen superrace are given for multilines of various compositions.Paper No. 9246 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, North Carolina. This investigation was supported in part by NIH Research Grant No. GM 11546 from the National Institute of General Medical Sciences     

Linkage analysis for 18 enzyme loci in Pinus rigida Mill.

Summary Estimates of recombination frequency among enzyme loci of pitch pine revealed two new linkages, Mdh3:Pgm2 (=0.01) and Pep1:Mdh4 (=0.38), and confirmed two previously established linkages. Tighter linkage (=0.30) was ruled out for nearly all gene pairs examined. In general, the Bayesian approach used in this study to test for linkage performed better than alternative methods.This work was supported by the School of Natural Resources, College of Agricultural and Life Sciences, University of Wisconsin, Madison, WI, and by McIntyre-Stennis, project no. 142-C385     

Multiline varieties and disease control

Summary Existing theoretical models have led to conflicting predictions concerning the likely effect of the widespread use of dirty crop multilines on the evolution of virulence in pathogen populations. Here we attempt to clarify these problems by extending existing models to include selection against unnecessary genes for virulence at two different stages in the life cycle of the pathogen. The results of these studies indicate that the stage of the life cycle at which selection occurs can significantly influence the evolution of virulence in pathogen populations growing on multiline varieties.     

Regeneration of Leydig cells in unilaterally cryptorchid rats: evidence for stimulation by local testicular factors

Summary Leydig cells in testes of adult rats were selectively destroyed by a single intraperitoneal injection of ethane dimethane sulphonate. Four days later rats were made unilaterally cryptorchid and 1, 2 and 4 weeks later the histology of the testes was examined by light microscopy and morphometry. After induction of unilateral cryptorchidism, the volume of abdominal compared to scrotal testes was reduced by 45–60% due to rapid impairment of spermatogenesis in abdominal testes. Leydig cells were not present in either scrotal or abdominal testes in the 1-week unilateral crytorchid group. A new generation of foetal-type Leydig cells was observed in scrotal testes of the 2-week unilateral crytorchid group although their total volume per testis estimated by morphometry, was small, being approximately 1 l. In contrast, the abdominal testis exhibited a remarkable proliferation of foetal-type Leydig cells (total volume per testis, 16 l) which predominantly surrounded the peritubular tissues of the seminiferous tubules. A similar morphology and pattern of Leydig cell development was observed in scrotal and abdominal testes of the 4-week unilateral cryptorchid group where total Leydig cell volume was 7 l vs 21 l, respectively. The results show that regeneration of a new population of Leydig cells occurs more rapidly in the abdominal testis than in the scrotal testis of the same animal. These observations suggest the possibility that augmentation of Leydig cell growth is mediated by local intratesticular stimulatory factors within the abdominal testis. Development of new Leydig cells from the peritubular tissue provides circumstantial evidence that the seminiferous tubules and in particular the Sertoli cells, are a likely source of agents that stimulate the growth of Leydig cells.     

Das visuelle System von Zonotrichia leucophrys gambelii

Zusammenfassung Der Verlauf der Sehbahn und die Lokalisation der optischen Zentren wurden bei Zonotrichia leucophrys gambelii (nordamerikanischer Ammernfink) nach einseitiger Augenexstirpation mit den Techniken von Nauta-Fink-Heimer, Bodian und Bielschowsky erforscht. Die Untersuchungen erstreckten sich über einen Zeitraum von 3 bis zu 120 Tagen nach der Operation. Zonotrichia leucophrys gambelii besitzt ein für Vögel typisches visuelles System. Die Hauptmasse der Optikusfasern endet im Stratum griseum et fibrosum superficiale des Tectum opticum. Weitere zentrale Endgebiete sind: Nucleus geniculatus lateralis, Nucleus lateralis anterior, Nucleus superficialis synencephali, Nucleus externus, tectales Grau und Nucleus ectomamillaris als Kern der basalen optischen Wurzel. Alle Fasern werden im Chiasma opticum total gekreuzt, auch der Tractus isthmo-opticus, ein efferentes Bündel, dessen Ursprung im Nucleus isthmo-opticus zu finden ist. Dieses efferente Fasersystem läßt sich im Stumpf des durchtrennten N. opticus noch 120 Tage nach der Operation gut versilbern. Eine direkte Verbindung von Retina und Hypothalamus war lichtmikroskopisch nicht nachweisbar. Neurosekretorisch aktive Zellen des Hypothalamus können zwar einen engen räumlichen Kontakt mit den optischen Fasern haben, Synapsen sind aber an diesen Stellen nicht zu erkennen. Es werden passagere Opticusfasern beschrieben, die auf dem Weg zum Nucleus lateralis anterior und Nucleus superficialis synencephali den Hypothalamus durchsetzen.

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Neurohistological and experimental studies of the visual system in Zonotrichia leucophrys gambelii

Summary The course of the optic pathways and the positions of the optic centers have been investigated with unilaterally enucleated white-crowned sparrows, Zonotrichia leucophrys gambelii, using the techniques of Nauta-Fink-Heimer, Bodian, and Bielachowsky. The investigation involved birds examined 3–120 days after enucleation. The white-crowned sparrow has a typically avian visual system. The major bundles of optic fibers terminate in the stratum griseum et fibrosum superficiale of the tectum opticum. Further terminal areas are the nucleus geniculatus lateralis, nucleus lateralis anterior, nucleus superficialis synencephali, nucleus externus, the tectal gray, and the nucleus ectomamillaris of the basal optic root. There is a complete crossing of all fibers in the chiasma, including those of the tractus isthmo-opticus, an efferent bundle with its origin in the nucleus isthmo-opticus. This efferent fiber system can be well impregnated in the stump of the sectioned optic nerve up to 120 days after the operation. No direct connection between the retina and hypothalamus could be demonstrated by light microscopy. Hypothalamic neurosecretory cells can occur in close contact with optic fibers but no synapses have been recognized. Some optic fibers pass through the hypothalamus enroute to the nucleus lateralis anterior and the nucleus superficialis synencephali.

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft. Herrn Prof. Dr. D.S. Farner, Department of Zoology, University of Washington, Seattle, Wash., danke ich für die Förderung dieser Studien (National Institutes of Health Research Grant No. 5 ROI NB 06187 to Professor D. S. Farner).     

Fine structure of aphid stylet routes in plant tissues in correlation with EPG signals

Abstract. Plant penetration by Aphis fabae (Scopoli) was recorded by the electrical penetration graph (EPG) technique and followed by stylectomy during wave-forms that were suspected of indicating sieve element punctures. The severed stylets in the plant tissue were subsequently processed for transmission electron microscopy (TEM) and sectioned either transverse or longitudinal to the stylets. Two completely serially sectioned probes from the epidermis to the phloem were reconstructed.
In one probe the stylet pathway went to a sieve element and showed many empty branches of salivary sheath material. Breaks in cell walls filled with sheath material demonstrated that the majority of cells bordering the track had been punctured, which supports earlier evidence from EPGs. All types of cells showed punctures and the highest number was found inside the vascular bundle. Very few cells died, which would appear to be important for virus transmission, and in others cellular reactions remained limited to some callose formation. The route of the stylets was intercellular and passed through the secondary wall material. The role of pectinase in intercellular penetration, and previous evidence for intracellular tracks are discussed. Most sieve elements had been punctured but only one was eventually accepted. Thus, reaching a sieve element in a host plant does not automatically imply its acceptance though the reason remains unclear. Gelation of phloem proteins was shown in the stylet canal.
In a second probe, plant cytological and morphological correlations with the EPG were emphasized. Probes by other aphid-plant combinations showed great similarity.