Estimates of Denitrification and Nitrification in Coastal and Estuarine Sediments

Denitrification and nitrification in sediments of Tama Estuary and Odawa Bay, Japan, were investigated by the combined use of a continuous-flow sediment-water system and a ¹⁵N tracer technique. At Odawa Bay, the nitrification rate was comparable to the nitrate reduction rate, and 70% of the N₂ evolved originated from nitrogenous oxides (nitrate and nitrite) which were produced by the action of nitrifying bacteria in the sediments. At Tama Estuary, the nitrate reduction rate was 11 to 17 times higher than the nitrification rate, and nitrogenous oxides derived from ammonium accounted for only 6 to 9% of the N₂ evolution by denitrification.     

Prostaglandin stimulation of adenosine 3',5'-monophosphate accumulation in cultured chondrocytes in the presence or absence of parathyroid hormone

The effect of prostaglandin analogues on the cyclic AMP level in cultured chondrocytes were examined. Prostaglandin E1 at 0.4 to 30 microM, increased the intracellular concentration of cyclic AMP in chondrocytes. Its effect was rapid, being evident within 1 min and reaching a maximum in 10 to 20 min. The maximum level was sustained until 30 min after its addition and then decreased gradually. Prostaglandin D2 and E2 also increased the cyclic AMP level in chondrocytes, but they had less effect than prostaglandin E1. Prostaglandin A1 had no effect on the nucleotide level in chondrocytes, although they markedly increased the level in fibroblasts. The time course of stimulation of cyclic AMP accumulation in chondrocytes by prostaglandin E1, D2 or E2 was quite different from that by parathyroid hormone (PTH): the effect of prostaglandin was slower and more sustained than that of PTH. PTH potentiated the effect of prostaglandin E1, E2, or D2 on the cyclic AMP level in chondrocytes and that the combined effects of prostaglandin and PTH were more than additive. Addition of an inhibitor of cyclic nucleotide phosphodiesterase with prostaglandin, PTH or both produced a synergistic effect on the accumulation of cyclic AMP in the chondrocytes. These findings suggest that prostaglandin E1, E2, and D2 increase the synthesis of cyclic AMP and that the combined effect of the prostaglandins and PTH on the cyclic AMP level in chondrocytes is partly attributed to the synergistic synthesis of cyclic AMP in the cells.     

Separation of the Effects of Photoperiod and Hormones on Sex Expression in Cucumber

The effects of photoperiod on the sex expression of cucumberflowers were examined in relation to the endogenous GA and ethyleneproduction with short day (SD)- and long day (LD)-sensitivecultivars under controlled environmental conditions. Growth of plants was greatly reduced under LD in both typesof cultivars. Reflecting this, GA activity was greater and ethyleneevolution less in plants grown under SD than in those underLD. However, the number of pistillate flowers increased underSD and LD in SD- and LD-sensitive cultivar, respectively, indicatingthat a change in sex expression did not coincide with hormonalchanges in the SD-sensitive cultivar. Thus, the effect of photoperiodon the sex expression was found to be separate, at least inpart, from the effect of GA or ethylene in cucumber. (Received September 16, 1982; Accepted December 7, 1982)     

Changes in Microtubules in Onion Leaf Sheath Cells during Bulb Development

Cortical microtubules are oriented transversely to the cellaxis in leaf sheath cells of onion plants (Allium cepa L. cv.Osaka-Okute) that have not started bulb formation. As the bulbdevelops and the leaf sheath cells swell, the microtubules becomedisoriented and scattered and finally disappear. The microtubuleinhibitors colchicine and cremart [O-ethyl O-(3-methyl-6-nitrophenyl)N-sec-butylphosphorothioamidate]cause swelling of leaf sheath cells and make the basal partof the plant bulbous. The cortical microtubules may have animportant role in regulating bulb development in onion plants. (Received August 21, 1982; Accepted December 6, 1982)     

Formation of Chlorophyll-Protein Complexes in Greening Cucumber Cotyledons in Light and then in Darkness

The changes in chlorophyll-protein complexes (CPs) in cucumbercotyledons during illumination and subsequent dark incubationwere studied by SDS-polyacrylamide gel electrophoresis. Whenetiolated cucumber seedlings were illuminated, chlorophyll wassynthesized and CPs were formed. In the early phase of greening(6 h of illumination), light-harvesting chlorophyll a/b-proteincomplex (LHCP) was the main GP. As the greening proceeded, P700chlorophyll a-protein complex (CP1) accumulated. When 6-h illuminatedseedlings were transferred to darkness, CP1 accumulated concomitantlywith a decrease in LHCP without new chlorophyll synthesis. Thechanges in the amounts of CPs in the dark became smaller withthe progress of greening and were not observed after 72 h ofillumination. These changes were confirmed by examining thechlorophyll/P700 ratio and the low temperature absorption spectrumof cotyledons. These results suggest that in the early phaseof greening, CPs were unstable and their chlorophyll moleculeseasily exchanged with those of other kinds of CPs. (Received October 14, 1982; Accepted December 1, 1982)     

Effect of TPA on the mutagenicity of caffeine in the soybean mutation test

12-O-Tetradecanoylphorbol-13-acetate (TPA) is a well-known tumor promoter in mouse-skin carcinogenesis. Its effects on mutagenesis in a soybean test system were examined, and the effects were judged from the appearance of spots of various colors on the leaves. When soybean seeds were treated with TPA plus 0.03% caffeine, the frequency of spots per leaf decreased significantly and in proportion to the concentration of TPA. TPA alone at concentrations of 1–20 μg/ml did not induce any mutations. Mutations induced by γ-rays were not affected by administration of TPA either before or after exposure to γ-rays. The mechanism of suppression by TPA of mutations induced by caffeine is discussed.     

Histochemical studies on the regeneration of aminergic nerves in rat cerebral artery after superior cervical ganglionectomy

The course of regeneration of aminergic nerves in rat cerebral arteries was studied by means of histochemical methods, after uni- or bilateral cervical sympathectomy. Degeneration of aminergic nerves started on day 1 and was complete between days 3 and 7 after surgery. Between weeks 4 and 6, regenerating nerves started to appear from the proximal internal carotid artery. Regenerated aminergic nerve fibres were generally unbeaded and intensity of fluorescence was weak. The circular nerves appeared earlier than the longitudinal ones. The number of regenerating nerves reached the maximum, between months 9 and 12, at about half the normal level. AChE activity of the cerebral arteries showed no significant changes at any stage.     

Molybdic and tungstic heteropolyanions for "ionic fixation" of acetylcholine in cholinergic motor nerve terminals

The treatment of neuromuscular junctions with phosphomolybdic acid (PMA) and silicotungstic acid (STA) heteropolyanions permits the visualization of electron dense precipitates in the synaptic vesicles of the cholinergic motor nerve terminals. At the light microscopic level, the uncolored molybdenum salt is visualized after reduction to molybdenum blue. The blue coloration is confined to the nerve terminals. Since PMA and STA are known as strong precipitating agents of quaternary ammonium compounds (cations) it is supposed that they have insolubilized in situ the acetylcholine (Ach) of the synaptic vesicles by means of a rapid ionic interaction. Furthermore, in spite of the strong acidity of PMA and STA solutions, the ultrastructure of the treated tissue is not significantly altered but on the contrary seems to be well preserved. The ionic insolubilization of Ach, added to the good preservation of the ultrastructure prompted us to use the term "ionic fixation".     

The ultrastructural basis of the permeability of arterial endothelium to horseradish peroxidase

The thoracic aorta and basilar artery, in which the incidence of atherosclerosis is known to be different, were examined to elucidate the correlation between the structure of the intercellular cleft junction between adjacent endothelial cells and its permeability to HRP. Tannic acid or HRP in the vessel lumen passed through the intercellular clefts of the thoracic aorta into the subendothelial space, whereas in the basilar artery they were unable to penetrate beyond the tight junction of the intercellular clefts. Freeze-fracture replicas revealed that the tight junctions of the thoracic aorta consisted of one to two junctional strands in most areas of the cleaved planes, with discontinuities in some places, whereas those of the basilar artery consisted of a continuous belt-like meshwork of six anastomosing junctional strands on average. These observations confirm that the structure of endothelial junctions in arteries has a close correlation with the permeability of the intercellular clefts to HRP.