Action of vasoactive intestinal peptide (VIP) on amphibian adrenocortical function,in vitro

Vasoactive intestinal peptide (VIP) is located in chromaffin cells of the frog adrenal gland and is able to stimulate corticosteroid secretion in amphibians. In the present study we have investigated the possible involvement of prostaglandins, microfilaments and calcium in the mechanism of action of VIP on frog adrenocortical tissue. Rana ridibunda interrenal dice were perifused with amphibian culture medium for more than 10 hours. Corticosterone and aldosterone concentrations were measured in the effluent perifusate using sensitive and specific radioimmunoassay methods. In the presence of indomethacin (5 μM), a specific blocker of prostaglandin biosynthesis, the spontaneous secretion of corticosteroids was markedly reduced (80%) but the stimulatory effect of VIP was not altered. The administration of the microfilament disrupting agent cytochalasin B (50 μM) inhibited both spontaneous and VIP-induced corticosteroid secretion. In the absence of calcium, the spontaneous level of corticosteroid was reduced to about 60% but VIP was still able to stimulate corticosteroid secretion. From these data we conclude that the integrity of the cytoskeleton is required for the secretory response of adrenocortical cells to VIP, whereas neither prostaglandins nor calcium are involved in VIP-induced adrenocortical stimulation.     

Synthesis and bioassay of isoprenoid 3-alkylthio-1,1,1-trifluoro-2-propanones: Potent,selective inhibitors of juvenile hormone esterase

Four 3-alkylthio-1,1,1-trifluoro-2-propanones with juvenile hormone-like side chains were prepared from citronellol and homogeraniol. These substrates were designed as possible transition-state analogs for the juvenile hormone (JH)-specific esterases present in insects. These four isoprenoid trifluoromethyl ketones were assayed in vitro with JH esterase and general esterases from larvae of the cabbage looper, Trichoplusia ni (Lepidoptera, Noctuidae), and with eel acetylcholinesterase and bovine chymotrypsin. JH esterase inhibition I₅₀ values were in the nanomolar range for all four compounds, while the other esterases had I₅₀'S which were 10³ to 10⁵ higher. The high selectivity of these inhibitors is believed to be due to their similarity in size and functionality to natural JH III. Treatment of T. ni larvae in vivo with solutions of the most active analog, 3-[(E)-4,8-dimethyl-3,7-nonadienylthio]-1,1,1-trifluoro-2-propanone (DNTFP) causes a dose-dependent delay in pupation and a concurrent selective inhibition of JH esterase. These data support the hypothesis that the reduction in in vivo JH titer in larval T. ni is due, in part, to hydrolysis of the hormone by selective esterases. DNTFP appears to be competing with JH for the active site of JH esterase.     

Microtubule arrays in the cortex and near the germinal vesicle of immature starfish oocytes

An extensive array of long, crisscrossing microtubules has been discovered in the cortex of oocytes of the starfish Pisaster ochraceus. The microtubules were visualized in cortex preparations by indirect immunofluorescence microscopy using antibodies to tubulin. The cortical array of microtubules is present in all oocytes before and for about 30 min after the application of 1-methyladenine, the hormone that induces oocyte maturation. The presence of microtubules was confirmed by electron microscopy. The microtubules in this array are depolymerized when oocytes are treated with colchicine or nocodozole and are augmented when oocytes are treated with taxol. Dihydrocytochalasin B treatment of the oocytes causes the microtubules to aggregate, presumably by altering a microfilament network also found in the cortex. The distribution of microtubules was also explored in whole oocytes stained with antitubulin. One or two aster-like structures were observed adjacent to the germinal vesicle of each oocyte.     

Growth,graviresponsiveness and abscisic-acid content of Zea mays seedlings treated with Fluridone

Ten-d-old seedlings of Zea mays L. cv. Tx 5855 treated with 1-methyl-3-phenyl-5-(3-[trifluoromethyl]phenyl)-4-(1H)-pyridinone (Fluridone) were analyzed for abscisic acid (ABA) content using high-performance liquid chromatography with an analysis sensitivity of 2.5 ng ABA g^-1 fresh weight (FW). Seedlings were divided into three portions: leaves, detipped roots, and root tips (terminal 1.5 mm). Control plants (water treatment only; no Fluridone) were characterized by the following amounts of ABA: leaves, 0.114±0.024 (standard deviation) g ABA g^-1 FW; detipped roots, 0.260±0.039±g ABA g^-1 FW; root tips, no ABA detected. We did not detect any ABA in tissues of Fluridone-treated plants. Primary roots of treated and untreated seedlings were strongly graviresponsive, with no significant differences between the curvatures or the growth rates of primary roots of Fluridone-treated and control seedlings. These results indicate that 1) Fluridone completely inhibits ABA synthesis, and 2) ABA is not necessary for positive gravitropism by primary roots of Zea mays.Abbreviations ABA abscisic acid - Fluridone 1-methyl-3-phenyl-5-(3-[trifluoromethyl]phenyl)-4-(1H)-pyridinone - FW fresh weight - SD standard deviation     

Light and Electron Microscopic Observations of Gametogenesis in Hastigerina pelagica (Foraminifera)*

SYNOPSIS. During gametogenesis mother individuals of Hastigerina pelagica (d'Orbigny) undergo significant morphological changes. Thirty h before gamete release, the cytoplasm changes from pale orange to bright red, possibly due to transport of stored lipids from the inner region to more peripheral parts of the cytoplasm. During the next 10 to 15 h the bubble capsule which surounds the calcareous shell is discarded. After all bubbles have disappeared, the individual sheds its spines by resorbing the spine bases close to the shell surface. A single mother nucleus divides into some hundreds of thousands of gamete nuclei within a span of ～ 20 h. A bulge of cytoplasm is extruded from the aperture and increases in size during the next 5 to 10 h. This bulge consists of cytoplasmic strands in which gametes and spherical bodies are embedded. The gametes and spherical bodies mature and are released during the afternoon and early evening. The gametes have 2 unequal acronematic flagella. A previously undescribed structure in foraminiferal reproduction is the spherical body which consists of a large vacuole surrounded by a thin cytoplasmic layer in which several nuclei, various typical cell organelles and multiple flagella are present. The spherical bodies are believed to play a role as receptacles of waste material, possibly including residual digestive enzymes, thereby protecting the gametes from lysis during the reproductive process. Fusion of gametes and further development into the next generation have not been observed.     

Concentration of iron and manganese in rice plants as influenced by hexachlorocyclohexane applied to soil

Summary Application of a granular formulation of hexachlorocyclohexane (HCH) to the potted soil at flooding decreased the concentration of iron and. to some extent, manganese in rice plants, especially at concentrations above 3 ppm active ingredient (a.i.) Likewise, HCH, applied to rice fields at transplanting (several days after submergence) caused a significant decrease in the concentration of iron, and not manganese, in the rice plant but only at concentrations above 12.5 kg a.i./ha despite high levels of reduced iron in the soil. Inhibition of iron reduction by HCH was more pronounced when applied at flooding than at several days after flooding.     

The nature of formate metabolism in greening barley leaves

The metabolism of [³H]formate has been examined in etiolated and greening leaves of barley (Hordeum vulgare), dwarf bean (Phaseolus vulgarls), broad bean (Vicia faba) and corn (Zea mays). Tritium was extensively incorporated by primary leaves incubated for 20-min periods in light or dark. The organic acids and free amino acids were the principal products of formate metabolism but these and other products were more heavily labelled in green tissues. Time course experiments with barley leaves revealed a rapid labelling of serine, accompanied by increasing amounts of ³H in glycine and aspartate as the feeding period was extended. These amino acid products were formed throughout a 4-day greening period with an approximate doubling in total incorporation being due to large accumulations of tritiated glycine and aspartate. The involvement of tetrahydrofolate-dependent reactions in formate metabolism was indicated by inhibition of [¹⁴C] and [³H]formate incorporation by the folate antagonist, aminopterin. Labelling of glycine and serine was also strongly inhibited (up to 90%) when the leaves were incubated with increasing concentrations of isonicotinylhydrazide.     

A simple and sensitive colorimetric method for the determination of long-chain free fatty acids in subcellular organelles

A colorimetric assay for the determination of long-chain free fatty acids (FFA) is described. The FFA were extracted from subcellular organelles with chloroform:heptane:methanol. The copper soaps of FFA were determined colorimetrically with diphenylcarbazide. There are three advantages to employing the present modified procedure. (a) The sensitivity has been increased approximately twofold over that of the previous procedure of K. Falholt, B. Lund, and W. Falholt (1973, Clin. Chim. Acta46, 105–111); (b) it takes less time to complete the assay compared to the tedious procedures currently available; and (c) the presence of bovine serum albumin, a known FAA-binding protein, does not interfere with the assay procedure. The assay shows a linear response over the range of 10 to 130 nmol of FFA. The recovery of free fatty acids from mitochondria is 99%.     

Purification of lipoamide dehydrogenase from Ascaris muscle mitochondria and its relationship to NADH:NAD+ transhydrogenase activity

Lipoamide dehydrogenase (NADH:lipoamide oxidoreductase EC 1.6.4.3) has been isolated from Ascaris suum muscle mitochondria. This activity has been purified to apparent homogeneity from both the pyruvate dehydrogenase complex and from 150,000g mitochondrial supernatants which were devoid of pyruvate dehydrogenase complex activity. The enzymes from both sources exhibited similar kinetic, catalytic, and regulatory properties and appear to be identical as judged by polyacrylamide gel electrophoresis. The native enzyme acts as a dimer, containing 2 mol of FAD, and has a subunit molecular weight of 54,000, as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel chromatography. The enzyme also possesses substantial NADH:NAD⁺ transhydrogenase activity. Heat denaturation and differential solubilization experiments imply that the transhydrogenase activity previously reported is, in fact, associated with the lipoamide dehydrogenase moiety of the Ascaris pyruvate dehydrogenase complex. Whether or not this activity functions physiologically in hydride ion translocation, as previously suggested, remains to be demonstrated.     

Fluence response relationship of carotenogenesis inNeurospora crassa

The fluence response of the blue light induced carotenoid synthesis inNeurospora is biphasic. Using fluence rates between 0.3 and 40 Wm^-2, increasing illumination times beyond 16 min (at 20°C) result in a second rise of the amount of carotenoids synthesized in the subsequent dark period. On altering the temperature, the transition point to the second phase of the response is shifted to shorter/longer illumination periods with increasing/decreasing temperature, respectively. The transition point can also be shifted by administering high fluence rates of near UV light: The start of the second phase is already triggered after an irradiation time of 2 min. The findings suggest that elements of the transduction sequence become depleted and senstivity recovers in a temperature-dependent process. The biphasic response and the effects of UV light are discussed in relation to the transduction mechanism and to the ecological significance.Presented in part at the meeting of the Deutsche Botanische Gesellschaft, September 1978, Marburg, Federal Republic of Germany