Morphometric and morphological delineation of southern African species of Aethomys (Rodentia: Muridae)

Five species of African rock rats, Aethomys namaquensis, A. granti, A. silindensis, A. nyikae and A. chrysophilus, have to date been recognized in southern Africa. While the first three species are craniometrically well-delineated, morphometric analysis of cytogenetically known and other specimens of A. chrysophilus revealed that it comprises two sympatric, morphologically similar species, the nominate species and the newly recognized A. ineptus. This is in agreement with observations on cranial morphology and earlier investigations involving cytogenetics, protein electrophoresis, and gross sperm and bacular morphology. Contrary to published reports, the Central African A. nyikae does not extend into southern Africa, and the single previous record from eastern Zimbabwe is probably based on a misidentification.     

The Effect of Calcium Starvation on Assimilate Partitioning and Mineral Distribution of the Phloem

Populus plants were grown in a medium lacking calcium and exposedto ¹⁴CO₂. In contrast to plants in the complete nutrient medium,the percentage amount of ¹⁴C-assimilates increased in the leavesof calcium-deficient plants and decreased in the stem and theroots. When plants were grown without potassium or magnesiumno differences in the amount of ¹⁴C-label occurred in comparisonwith plants in the complete nutrient medium. Translocation wasrecorded by microautoradiography. It was observed that considerableamounts of labelled photoassimilates were unloaded from thephloem in the middle part of the stem in plants of the completenutrient medium. In contrast, during calcium starvation ¹⁴C-labelwas restricted to the phloem of the stem. In addition, the concentrationsof magnesium and phosphorus showed a remarkable increase instem sieve tubes of calcium-deficient plants. When sieve tubesof source leaves from Populus, barley and maize were comparedwith those of sink leaves, the latter showed higher calciumconcentrations. The results suggest that calcium is a necessaryfactor in the regulation of phloem translocation. Key words: Calcium deficiency, phloem translocation, sieve element loading and unloading, X-ray microanalysis     

Modulation of Normal Human Melanocyte Dendricity by Growth-Promoting Agents

Dendrite formation and extension, which comprise a characteristic morphology of human normal melanocytes in the skin, represent one of the functional activities of melanocytes, the ability to transfer melanosomes into neighboring keratinocytes. However, the morphology of the melanocyte in vitro is usually quite different from that observed in vivo. it is probably due to the hyperproliferative condition of the melanocytes in culture. No studies have ever compared the effects of a single factor on both dendricity and proliferation at the same time. Therefore, we have compared the effects of six growth-promoting agents commonly used for melanocyte cultures on dendrite formation and proliferation. The addition of agents that increase the intracellular levels of cyclic adenosine monophosphate (cAMP)—dibutyryl cyclic adenosine monophosphate (db cAMP; 1 mM) or isobutylmethyl xanthine (IBMX; 0.1 mM)—had a strong effect on dendrite formation and a negative effect on proliferation. This was especially true with db cAMP. In the presence of 2% or 5% of heat-inactivated fetal bovine serum (FBS), dendrite formation was significantly increased as was proliferation. The number of dendrites was decreased in the culture with 12-o-tetradecanoylphorbol-13-acetate (TPA), but cell growth was slightly increased. With human recombinant basic fibroblast growth factor (bFGF) (0.5, 1.0 ng/ml) in the presence of bovine pituitary extract (BPE) (60 μg/ml), cell growth was increased. With 2 ng/ml of bFGF, however, a strong inhibitory effect on proliferation was observed. However, dendrite formation was constant at all concentrations of bFGF tested (0.5, 1.0 or 2.0 ng/ml) with BPE (30 or 60 μg/ml). In this study, we have demonstrated that dendrite formation was suppressed by the reagents that stimulate melanocyte proliferation, and vice versa, with the only exception being heat-inactivated FBS. Both dendrite formation and proliferation were induced by the heat-inactivated FBS. This approach is crucial to the development of an adequate culture system for proliferation and/or dendrite formation of normal human melanocytes. It is necessary to keep these aspects in mind as we further investigate the biology of melanocytes, especially the cell-to-cell interactions between melanocytes and keratinocytes, involved in melanogenesis and melanin pigmentation in vivo. This study also provides practical and important information for a future reconstitutive skin system composed of melanocytes, keratinocytes, and fibroblasts in a single culture medium.     

Characterization of Sulphate Uptake in Anacystis nidulans

Sulphate uptake in the blue-green alga Anacystis nidulans appears based upon an active mechanism with a Km of 0.75 μM and V_max of 0.7 pmol/min × 10⁶ cells. Sulphate uptake is competitively inhibited by thiosulphate and sulphite. The sulphate uptake has a pH optimum at 8 and a temperature optimum at 40°C. By increasing the extracellular sulphate concentration from 0.1 to 10 μM the sulphate pool in Anacystis was altered from 8.3, 10^?5M to 5.9, 10^?4M.     

PHOSPHATIZED SOFT-TISSUE IN TRIASSIC BIVALVES

Abstract: Exceptionally preserved specimens of the genera Myophoria, Neoschizodus and Trigonodus (Bivalvia, Palaeoheterodonta, Trigonioida) from carbonate sediments of the Muschelkalk (Anisian, Ladinian) contain phosphatized soft‐tissues. This is the oldest record of soft‐tissue preservation in bivalves and the first from the German Muschelkalk. The phosphatized remains are here interpreted as relics of the originally chitinous gill supports, the gill axis, the labial palps (?), the adductor muscles, the pedal retractor muscles, the mantle margin including the radial mantle musculature, and the ‘siphons’. According to microprobe analysis, the mineral replacing the soft‐tissue is mainly apatite and, more rarely, francolite. Additionally, quartz filled voids within the gill supports, and in one sample it occurs in minute crystals in the phosphatized remains of the adductor muscle of Neoschizodus. Myophoria, Neoschizodus and Trigonodus were soft‐bottom dwellers and five of the specimens were discovered in life position. This is indicated by geopetal structures in three specimens.     

Nine polymorphic microsatellite loci for the parasitic wasp Neotypus melanocephalus (Hymenoptera: Ichneumonidae)

Nine polymorphic microsatellite loci were isolated from Neotypus melanocephalus (Gmelin), a parasitoid of the parasitic large blue butterfly Maculinea nausithous. Allelic diversity and heterozygosity were quantified in samples from the Upper Rhine valley in Southwest Germany.