Morphological investigations on follicular atresia in canine ovaries

Summary Morphologically, canine ovaries show two types of regression pattern in secondary follicles. In type A necrotic changes of the oocytes and the zona pellucida dominate, whereas in type B degeneration, necrobiosis and necrosis of the granulosa prevail. The atretic course of type B regression results in a pseudoantrum and leads, by pseudogrowth, to a structure imitating tertiary follicles. In both type A and type B regression, four consecutive stages of atresia are distinguished by light- and electron microscopy.True tertiary follicles display only one regression pattern which resembles type B of secondary follicles. Early, advanced, late, and terminal stages of atresia are again described.     

Arbuscular mycorrhizal colonization of halophytes in Central European salt marshes

 Halophytes from both coastal and inland Central European salt marshes were examined for colonization by arbuscular mycorrhizal (AM) fungi. Plants from different families were strongly colonized but the degree of colonization varied with the individual plant and apparently during the vegetation period, too. Members of the typical non-mycorrhizal families like Armeria maritima of the Plumbaginaceae and Salicornia europaea of the Chenopodiaceae were found to be colonized, particularly in the drier salt marshes. High numbers of Glomus spores were found in the saline soils, especially those of the inland locations examined. Approximately 80% of these spores were from Glomus geosporum as shown by a typical restriction fragment length polymorphism (RFLP) pattern of the amplified internal transcribed spacer regions. The present study demonstrates that RFLP analysis is useful when screening habitats for the occurrence of mycorrhizal fungi which can be identified only with difficulty by morphological criteria. Accepted: 25 August 2000     

Social facilitation of male song by male and female conspecifics in the zebra finch, Taeniopygia guttata

Zebra finches are a ubiquitous model system for the study of vocal learning in animal communication. Their song has been well described, but its possible function(s) in social communication are only partly understood. The so-called ‘directed song’ is a high-intensity, high-performance song given during courtship in close proximity to the female, which is known to mediate mate choice and mating. However, this singing mode constitutes only a fraction of zebra finch males’ prolific song output. Potential communicative functions of their second, ‘undirected’ singing mode remain unresolved in the face of contradicting reports of both facilitating and inhibiting effects of social company on singing. We addressed this issue by experimentally manipulating social contexts in a within-subject design, comparing a solo versus male or female only company condition, each lasting for 24 h. Males’ total song output was significantly higher when a conspecific was in audible and visible distance than when they were alone. Male and female company had an equally facilitating effect on song output. Our findings thus indicate that singing motivation is facilitated rather than inhibited by social company, suggesting that singing in zebra finches might function both in inter- and intrasexual communication.     

Origins and functional diversification of salinity‐responsive Na+, K+ ATPase α1 paralogs in salmonids

The Salmoniform whole‐genome duplication is hypothesized to have facilitated the evolution of anadromy, but little is known about the contribution of paralogs from this event to the physiological performance traits required for anadromy, such as salinity tolerance. Here, we determined when two candidate, salinity‐responsive paralogs of the Na⁺, K⁺ ATPase α subunit (α1a and α1b) evolved and studied their evolutionary trajectories and tissue‐specific expression patterns. We found that these paralogs arose during a small‐scale duplication event prior to the Salmoniform, but after the teleost, whole‐genome duplication. The ‘freshwater paralog’ (α1a) is primarily expressed in the gills of Salmoniformes and an unduplicated freshwater sister species (Esox lucius) and experienced positive selection in the freshwater ancestor of Salmoniformes and Esociformes. Contrary to our predictions, the ‘saltwater paralog’ (α1b), which is more widely expressed than α1a, did not experience positive selection during the evolution of anadromy in the Coregoninae and Salmonine. To determine whether parallel mutations in Na⁺, K⁺ ATPase α1 may contribute to salinity tolerance in other fishes, we studied independently evolved salinity‐responsive Na⁺, K⁺ ATPase α1 paralogs in Anabas testudineus and Oreochromis mossambicus. We found that a quarter of the mutations occurring between salmonid α1a and α1b in functionally important sites also evolved in parallel in at least one of these species. Together, these data argue that paralogs contributing to salinity tolerance evolved prior to the Salmoniform whole‐genome duplication and that strong selection and/or functional constraints have led to parallel evolution in salinity‐responsive Na⁺, K⁺ ATPase α1 paralogs in fishes.     

Carbon partitioning in Arabidopsis thaliana is a dynamic process controlled by the plants metabolic status and its circadian clock

Plant growth involves the coordinated distribution of carbon resources both towards structural components and towards storage compounds that assure a steady carbon supply over the complete diurnal cycle. We used ¹⁴CO₂ labelling to track assimilated carbon in both source and sink tissues. Source tissues exhibit large variations in carbon allocation throughout the light period. The most prominent change was detected in partitioning towards starch, being low in the morning and more than double later in the day. Export into sink tissues showed reciprocal changes. Fewer and smaller changes in carbon allocation occurred in sink tissues where, in most respects, carbon was partitioned similarly, whether the sink leaf assimilated it through photosynthesis or imported it from source leaves. Mutants deficient in the production or remobilization of leaf starch exhibited major alterations in carbon allocation. Low‐starch mutants that suffer from carbon starvation at night allocated much more carbon into neutral sugars and had higher rates of export than the wild type, partly because of the reduced allocation into starch, but also because of reduced allocation into structural components. Moreover, mutants deficient in the plant's circadian system showed considerable changes in their carbon partitioning pattern suggesting control by the circadian clock.     

Phthalates Are Metabolised by Primary Thyroid Cell Cultures but Have Limited Influence on Selected Thyroid Cell Functions In Vitro

Phthalates are plasticisers added to a wide variety of products, resulting in measurable exposure of humans. They are suspected to disrupt the thyroid axis as epidemiological studies suggest an influence on the peripheral thyroid hormone concentration. The mechanism is still unknown as only few in vitro studies within this area exist. The aim of the present study was to investigate the influence of three phthalate diesters (di-ethyl phthalate, di-n-butyl phthalate (DnBP), di-(2-ethylhexyl) phthalate (DEHP)) and two monoesters (mono-n-butyl phthalate and mono-(2-ethylhexyl) phthalate (MEHP)) on the differentiated function of primary human thyroid cell cultures. Also, the kinetics of phthalate metabolism were investigated. DEHP and its monoester, MEHP, both had an inhibitory influence on 3''-5''-cyclic adenosine monophosphate secretion from the cells, and MEHP also on thyroglobulin (Tg) secretion from the cells. Results of the lactate dehydrogenase-measurements indicated that the MEHP-mediated influence was caused by cell death. No influence on gene expression of thyroid specific genes (Tg, thyroid peroxidase, sodium iodine symporter and thyroid stimulating hormone receptor) by any of the investigated diesters could be demonstrated. All phthalate diesters were metabolised to the respective monoester, however with a fall in efficiency for high concentrations of the larger diesters DnBP and DEHP. In conclusion, human thyroid cells were able to metabolise phthalates but this phthalate-exposure did not appear to substantially influence selected functions of these cells.