Selectivity of juxtaposition between cup-shaped lactotrophs and gonadotrophs from rat anterior pituitary in culture

Summary Semi-thin sections of three-dimensional reaggregates from adult female rat pituitary, cultured in serum-free defined medium, were stained for prolactin, gonadotropin, thyrotropin, growth hormone and S-100, using the double immunolabelling technique. The frequency of juxtaposition between lactotrophs and gonadotrophs was enumerated and compared with the expected frequency at random distribution of polygonal cell profiles in a hexagonal configuration. The proportions of lactotrophs and gonadotrophs in the aggregate sections were determined using stereometrical analysis. The observed frequency of juxtaposition did not differ significantly from the expected frequency. Hence, no reason was found to assume a selective adhesion between lactotrophs and gonadotrophs in adult female rat pituitary reaggregates. A constant proportion of lactotrophs was found to meet the criteria of a cup-shaped morphology, and 70%±9% (mean ±S.D.) of these so-called cupshaped lactotrophs were found to be juxtaposed at their concave side to gonadotrophs. Administration of 0.01 nM 17-oestradiol to the culture medium resulted in a significant reduction of the proportion of cup-shaped lactotrophs but did not affect the selectivity of juxtaposition to gonadotrophs. The selectivity of juxtaposition between cup-shaped lactotrophs and gonadotrophs may be the morphological correlate of the functional relationship between these cells, which are known to be involved in an intra-pituitary paracrine communication system.     

Microbially Mediated Mn(II) Oxidation in an Oligotrophic Arctic Lake

Rates of oxidation of Mn(II) were measured by an in situ incubation technique in the water column of Toolik Lake, Alaska. Measured rates were lower than those observed in other aquatic systems but were sufficient to oxidize all Mn(II) in the lake within a 3-month period. Measured rates compared favorably with rates estimated from a previous study of the geochemical cycling of Mn in Toolik Lake. The Mn(II) oxidation was largely microbially mediated, as indicated by inhibition of oxidation rates by sodium azide. Azide had been previously demonstrated to be a suitable microbial poison for studying Mn(II) oxidation in seawater. This study demonstrates that azide is also a suitable poison for freshwaters and that it inhibits microbial but not abiotic oxidation of Mn(II). Manganese(II) oxidation rates were similar during cold, under-ice conditions in early spring and during warmer summer conditions. This observation suggests that Mn(II) concentration, rather than temperature or oxygen concentration, is the most important factor regulating Mn(II) oxidation rates in Toolik Lake.     

Organic free radical levels in seeds and pollen: The effects of hydration and aging

In view of their possible role in oxidative deterioration of seeds and pollen, organic free radicals were measured by electron spin resonance in embryonic axes and cotyledons of soybean [ Glycine max (L.) Merr], embryo and endosperm fractions of corn [ Zea mays L.] and pollen of cattail [ Typha latifolia L.]. A pronounced decline in the radical signal ensued when hydration increased above about 7% (wet weight basis) in both the seed materials and in pollen. Moderate hydration of the soybean axis followed by drying led to a small decrease in organic free radicals compared to untreated material, especially if the desiccation step was performed under nitrogen. In a comparison of soybeans of various ages under normal storage, organic free radical levels in the axis showed little or no increase with age. In marked contrast, over 5 days of accelerated aging at 40°C and near-saturating humidity, organic radical levels approximately doubled in the axis. This pronounced increase in free radical content was not associated with a decrease in the proportion of polyunsaturated fatty acids. The data suggest that hydration of seed and pollen causes a release of free radicals from the trapped state.     

Distribution of calcium,magnesium and inorganic phosphate in plasma of estradiol-17β treated rainbow trout

Summary Freshwater rainbow trout,Salmo gairdneri, were injected with different doses of estradiol-17 in order to induce the synthesis of a protein, regarded as identical to vitellogenin. The plasma levels of free and protein-bound calcium, magnesium and inorganic phosphate were studied in control and estradiol-17 treated fish, using an ultrafiltration method. Estradiol-17 caused a dose-dependent increase in plasma vitellogenin levels, which strongly correlated to protein-bound levels of calcium and magnesium in plasma. Calcium and magnesium were bound to vitellogenin in a ratio of 9:1, which was considerably higer than the protein-binding ratio of these ions in normal plasma (5.2:1). The dose-dependent increase in total plasma levels of calcium, magnesium and inorganic phosphate during estradiol-17 treatment was solely due to an increase in the protein-bound fraction of these ions. It is concluded that the physiologically important plasma levels of free calcium, magnesium and inorganic phosphate are effectively regulated at normal levels during vitellogenin synthesis.     

Mating behavior,egg deposition,incubation period,and hatching in the clearnose skate,Raja eglanteria

Synopsis Adult clearnose skates, Raja eglanteria, were captured during the winters of 1981 and 1983, and observed to mate in captivity. Mating and egg depositions take place on the central west coast of Florida from December through mid-May. During copulation the male holds the trailing edge of the female's right or left pectoral fin firmly in his mouth, swings his tail beneath hers and inserts one clasper into the distal end of her reproductive tract. Copulation may last one to four hours during which time sperm pass from the urogenital papilla of the male along the clasper groove to the female. Sperm move cranially to the upper portion of the shell gland where they are stored and remain viable for at least three months. The ovum is fertilized in the shell gland. The egg case bears a prominent projection or horn at each corner. The two posterior ones are shorter and bear tendrils which are covered with a sticky substance that insures attachment to the substrate when the egg is deposited. Fertilized eggs are laid in pairs at intervals ranging from 1 to 13 days (mean of 4.5 ± 2.2 days). As development proceeds within the egg case a plugged slit on the lateral side of each horn opens and permits seawater to wash the developing embryo. Incubation periods for eggs maintained between 20–22°C decrease in duration throughout the egg laying season, ranging from 94 days initially to 77 days for eggs laid later in the spring. At hatching, the anterior end of the egg case ruptures, and the skate emerges abruptly with its pectoral fins rolled dorsally.     

Correlations of understory herb distribution patterns with microhabitats under different tree species in a mixed mesophytic forest

Summary This study examines the role of canopy trees in the formation and maintenance of different herb microhabitats in a mixed mesophytic forest stand. Herb abundance and reproductive success were recorded in 54 circular plots under seven species of canopy trees and in 15 circular control plots>2 m from any tree. Soil moisture, soil nutrient levels, litter depth, and light intensity were measured in a subset of these plots. Ordination of plots by both herb relative abundance and by reproductive success of common species indicated that herb assemblages under most canopy tree species were similar to those away from trees. However, herb assemblages under Fagus grandifolia trees differed moderately from the others while plots under Quercus alba trees supported significantly different herb assemblages. Analyses of variance revealed that several herb species occurred at significantly closer mean distance to the base of Q. alba or Fagus trees or at higher densities under these tree species. Soils around Q. alba trees had significantly higher concentrations of calcium and sulfate ions, and higher pH than plots under other tree species and control plots. This correlated closely with Q. alba stemflow which had higher concentrations of calcium and sulfate ions and lower concentrations of hydrogen ions than stemflow from other trees at this site. The slightly lower soil pH near the base of Fagus trees may have been related to the high volumes of stemflow produced by this species. Stepwise regression showed significant correlations between abundances of five common herb species and soil nutrient patterns. Maintenance of spatial heterogeneity in forest floor resources by the presence of different species of canopy trees may therefore be important in the maintenance of diversity in these understory herb communities.