Cyclic AMP regulation of Gs protein. Thyrotropin and forskolin increase the quantity of stimulatory guanine nucleotide-binding proteins in cultured thyroid follicles

This study was carried out to clarify the way in which thyrotropin (TSH) and forskolin regulate the adenylylcyclase complex in thyroid follicle cells. We examined the effects of chronic treatment of pig thyroid follicles with TSH or forskolin on the state of G proteins by (a) assaying adenylylcyclase activity, (b) analyzing the ADP-ribosylation of stimulatory G protein (Gs) by cholera toxin, and (c) quantifying the Gs subunits by Western blotting with antipeptide antibodies. Chronic exposure (18 h) of thyroid follicles to a low concentration of TSH (0.01-0.1 milliunit/ml) enhanced the subsequent response of adenylylcyclase to TSH. Higher concentration of TSH (1 milliunit/ml) induced a homologous desensitization of this response. In cells pretreated with forskolin, the TSH-stimulated adenylylcyclase activity was higher than in control cells. The forskolin-or guanosine 5'-(beta, gamma-imido) triphosphate (Gpp(NH)p)-stimulated adenylylcyclase activity was always significantly increased after chronic treatment of cells with TSH or forskolin. Treatment of cultured thyroid follicle membranes with [32P]NAD and cholera toxin resulted in labeling of the Gs alpha (45-52-kDa) component. Culturing follicles with TSH (0.001-1 milliunit/ml) or forskolin (0.01-10 microM) greatly affected the cholera toxin-mediated ADP-ribosylation of the Gs alpha subunit. Gs alpha labeling increased progressively to level off at 1 milliunit/ml TSH or 1 microM forskolin (150-200%). Gs alpha immunoreactivity was increased in parallel (200-300%). The immunoreactivity of G beta subunits in cells cultured with TSH or forskolin was also increased compared with control cells. Cycloheximide abolished the effects of TSH and forskolin on the follicles, suggesting that new protein synthesis is required. These results indicate that Gs protein subunits are up-regulated by TSH and forskolin and suggest that their synthesis in thyroid cells is mediated, at least in part, by a cyclic AMP-dependent mechanism.     

Microbial biofilm inoculants benefit growth and yield of chrysanthemum varieties under protected cultivation through enhanced nutrient availability

Protected cultivation of ornamental flowers, as a commercial venture, becomes less profitable with excessive use of fertilizers. The present study examined the influence of microbial biofilm inoculants (Anabaena–Azotobacter, Anabaena–Trichoderma and Trichoderma–Azotobacter) on the availability of soil nutrients and structure of rhizosphere microbial communities in three varieties of chrysanthemum (var. White Star, Thai Chen Queen and Zembla). Varietal-specific responses in growth, enzyme activities, flower yield of plants and availability of soil nutrients were recorded. Dehydrogenase activity was highest in var. White Star treated with the Anabaena–Trichoderma biofilm inoculants. The Anabaena–Azotobacter inoculant enhanced the availability of nitrogen, phosphorus and micronutrients in the soil, besides 40–50% increase in soil organic carbon, as compared to carrier alone or no inoculation. PCR-DGGE profiling of the cyanobacterial communities and qPCR quantification of 16S rRNA abundance of bacteria, archaea and cyanobacteria in the rhizosphere soils, revealed the stronger influences of these inoculants, especially in var. Zembla. Principal Component Analysis (PCA) helped to illustrate that the enhanced microbe-mediated availability of soil macro-and micronutrients, except iron content (Fe), was the most influential factor facilitating improved plant growth and yield parameters. The Anabaena–Azotobacter, and Anabaena–Trichoderma biofilm inoculants, proved superior in all three chrysanthemum varieties.     

Thorn fish Terapon jarbua (Forskål) predation on juvenile white shrimp Penaeus indicus H. Milne Edwards and brown shrimp Metapenaeus monoceros (Fabricius): the effect of turbidity, prey density, substrate type and pneumatophore density

A series of laboratory experiments was conducted at Inhaca Island Marine Biological Station, Mozambique, in order to assess the separate effects of turbidity, prey density, substrate type, pneumatophore density, and the combined effects of turbidity with the latter three, on rate of predation by the thorn fish Terapon jarbua (Forskål, 1775) on white shrimp Penaeus indicus and brown shrimp Metapenaeus monoceros.Significant interactions between turbidity and the other three factors on shrimp predation for both prey species were detected. Regardless of prey density, increasing turbidity decreased predation on P. indicus, but not on M. monoceros, for which increasing densities reduced the protective effect of turbidity. Increasing prey density increased predation on P. indicus in clear water, and increased predation on M. monoceros in low and high, but not in intermediate turbidity or clear water. The presence of a substrate suitable for burying decreased predation on M. monoceros in clear water, but not in the turbidity levels used. In clear water, solely sandy-shell substrate afforded protection to P. indicus, while in turbid water, no substrate offered significant protection and muddy substrate even increased prey vulnerability to fish probably as a result of increased preys' locomotor activity. Raising pneumatophores density seems to lower the protective value of turbidity for both species. In clear water, only low and high structure density provided a deterrent effect on predation on P. indicus; in turbid water, intermediate and higher structure density increased predation. Increasing structural complexity reduced predation on M. monoceros linearly in clear water; but in low turbid water it increased. In high turbid waters, the increase was only significant in intermediate pneumatophore density. High structural complexities impair the pursuing capacity of fish and thus decreased predation rates. The results indicate that the effective provision of shelter of different habitats depends not only on the various environmental parameters analysed, but also on the way they interact and on the behaviour of prey and predator as well.     

A new and rapid method for monitoring the new oxazolidinone antibiotic linezolid in serum and urine by high performance liquid chromatography-integrated sample preparation

A sensitive and rapid HPLC-assay for determining the new oxazolidinone antibiotic linezolid in serum and urine is described. HPLC-integrated sample preparation permits the direct injection of serum and urine samples without any pre-treatment. The in-line extraction technique is realized by switching automatically from the extraction column to the analytical column. After the matrix has passed the extraction column the retained analyte will be quantitatively transferred to the analytical column where separation by isocratic HPLC will be performed. Linezolid is detected according to its absorption maximum at 260 nm. The quantification limits are estimated to be 0.3 and 0.5 μg/ml in serum and urine samples, respectively. The described procedure allows sample clean-up and determination of the antibiotic within 20 min, thereby facilitating drug-monitoring in clinical routine.     

Transverse Vein Differentiation Associated with Gas Space Formation--Fate of the Middle Cell Layer in Leaf Sheath Development of Rice

In monocotyledons, the leaf vascular network consists of a hierarchicalsequence of vertical vascular bundles and numerous transverseveins that interconnect adjacent vertical veins. In the leafsheath of these species, especially grasses, lysigenous gascavities (gas spaces) are developed into intervascular spacesand provide a gas conducting system to non-aerial parts underflooded conditions. The spatial relationship between gas spaceformation and transverse vein differentiation was investigatedusing the leaf sheath of rice (Oryza sativa L.). Histochemicalobservation showed that patterns of differentiation of the transversevein are distinct from those of vertical vascular bundles. Onthe other hand, gas spaces are formed through the processesof cell death (collapse). Both events are initiated at a specificcell position in the middle layers of the leaf sheath, fromwhich the vascular system of the leaf is derived; this indicatesthat differentiation of transverse veins is associated withgas space formation. The cell-to-cell movement of fluoresceinisothiocyanate-conjugated dextran injected into middle layercells coincided with the area where cell collapse occurred,indicating a close relationship between the middle and adaxialcell layers, but not abaxial cell layers. A uniform cell numberbetween each transverse vein in the leaf sheath suggested theinvolvement of spatial regulation in transverse vein formationregardless of clonal history at the later stage of leaf veincanalization. Copyright 2000 Annals of Botany Company Cell collapse, leaf development, middle cell layer, microinjection, Oryza sativa L., rice, programmed cell death.