Plant responses to H2S and SO2 fumigation. I. Effects on growth, transpiration and sulfur content of spinach

Exposure of spinach (Spinacia oleracea L. cv. Monosa) to 0.25 μl l_?1 H₂S reduced the relative growth rate by 26, 47 and 60% at 15, 18 and 25°C, respectively. Shoot to root ratio decreased in plants fumigated at 18 and 25°C. Growth of spinach was not affected by a 2-week exposure to 0.10 or 0.25 μl l_?1 SO₂. Both H₂S and SO₂ fumigation increased the content of sulfhydryl compounds and sulfate. A 2-week exposure to 0.25 μl l_?1 H₂S resulted in an increase in sulfhydryl and sulfate content of 250 to 450% and 63 to 248% in the shoots, respectively, depending on growth temperature. Exposure to 0.15 and 0.30 μl l_?1 H₂S at 20°C for 2 weeks resulted in a 46% increase in sulfate content of the shoots at 0.30 μl l_?1 and no detectable increase at 0.15 μl l_?1 H₂S; the sulfate content of the roots increased by 195 and 145% at 0.15 and 0.30 μl l_?1 H₂S, respectively. Fumigation with 0.25 μl l_?1 SO₂ at 20°C for 2 weeks resulted in an increase in sulfhydryl content and sulfate content in the shoots of 285% and 300 to 1100%. H₂S fumigation during the 12 h light period or only during the dark period resulted in identical growth reduction and accumulation of sulfhydryl compounds; they were about 50 and 67% of those observed in continuously exposed plants. H₂S- and SO₂-exposed plants showed an increased transpiration rate, which was mainly caused by an increased dark-period transpiration. No effect of H₂S and SO₂ on the water uptake of the plants and the osmotic potential of the leaves was detected. Plants fumigated with 0.25 μl l_?1 H₂S for 2 weeks were smaller and differed morphologically from the control plants by slightly more abaxially curved leaf margins. Cross sections of the leaves showed smaller cells at the margins and smaller and fewer air spaces. The increased transpiration in the H₂S-exposed plants is discussed in relation to the observed morphological changes.     

Indomethacin antagonizes the ethanol-induced suppression of breathing activity but not the suppression of brain activity in the near-term fetal sheep

The effect of indomethacin on the ethanol-induced suppression of fetal breathing movements, low-voltage electrocortical (ECoG) activity, and electro-ocular (EOG) activity was studied in the near-term fetal sheep. Ten conscious instrumented pregnant ewes (between 129 and 131 days of gestation; term, 147 days) received 1-h maternal intravenous infusion of 1 g ethanol/kg total body weight and simultaneous fetal treatment with either indomethacin (2 mg/kg fetal body weight/h) (n = 5) or an equivalent volume of phosphate buffer (n = 5) intravenously for 9 h. Fetal ECoG activity, EOG activity, and fetal breathing movements were monitored continuously over the experimental periods. In animals treated with ethanol and buffer (n = 5), fetal breathing movements were suppressed for 8 h and low-voltage ECoG and EOG activity was suppressed for 2 h below preinfusion levels. In animals treated with ethanol and indomethacin (n = 5), fetal breathing movements were elevated for 13 h but low-voltage ECoG and EOG activity remained suppressed for 3 h below preinfusion levels. The data suggests that indomethacin can antagonize the ethanol-induced suppression of fetal breathing movements, but does not alter the ethanol-induced suppression of ECoG or EOG activity.     

Light Affects Flagellar Agglutinability in Chlamydomonas eugametos by Modification of the Agglutinin Molecules

The effect of light on the sexual competence of a light-sensitive mating type minus strain (mt⁻) of Chlamydomonas eugametos obtained by crossing a light-sensitive mating type plus strain (mt⁺) with a light-insensitive mt⁻ strain is described. As previously demonstrated for the mt⁺ parent, this study of one of the mt⁻ offspring shows that (a) a light-sensitive mechanism affects flagellar agglutinability in a rapid process that does not require protein synthesis; (b) only the activity of the flagellar agglutinins (glycoproteins responsible for agglutination) is susceptible to light while agglutinins on the cell body surface are not affected by light. We further demonstrate that (a) membrane vesicles naturally released from nonagglutinable dark gametes remain inactive. Extracts of these vesicles also remain inactive even though they contain agglutinin-like components; (b) inactive mt⁻ agglutinin is present in extracts of flagella from nonagglutinable dark gametes by comparison of its chromatographic, electrophoretic, and immunogenic properties with those of active agglutinin. When purified of all other flagellar proteins, it remains inactive; (c) a monoclonal antibody directed against the sexual agglutination site of the mt⁻ agglutintin discriminates between active and inactive agglutinins when present in a native state on the flagellar surface, but is unable to discriminate between them when they are denatured in sodium dodecyl sulfate-electrophoresis gels and blotted onto nitrocellulose. Taken collectively these observations suggest that light activation involves the chemical modification of the agglutinins in situ on the flagellar surface.     

Endogenous oscillator controls surface density of mating receptors in Chlamydomonas eugametos

Summary We describe a circadian rhythm in the surface density of receptors that play a dominant role in the mating process of the unicellular green alga Chlamydomonas eugametos.These receptors — called agglutinins — are large glycoproteins extrinsically bound to the membrane of gamete flagella. We found circadian fluctuations in their density. Since inhibition of protein synthesis affected the agglutinin density without a lag period at any time,we conclude that the density was dependent on de novo synthesis and that the fluctuations in density are caused by circadian oscillations in the rate of agglutinin synthesis. This phenomenon evidently underlies the pronounced endogenous rhythm in mating competence that we described previously (Demets et al. 1987). Finally, we speculate on the nature of the time keeping mechanism that is generating these rhythmic events.     

Ethanol Activates Maxi Ca2+-activated K+ Channels of Clonal Pituitary (GH3) Cells

The effect of ethanol on maxi Ca²⁺-activated K⁺ channels (BK channels) in GH3 pituitary tumor cells was investigated using single-channel recordings and focusing on intracellular signal transduction. In outside-out patches, ethanol caused a transient concentration-dependent increase of BK-channel activity. 30 mm (1.4‰) ethanol significantly increased mean channel open time and channel open probability by 26.3 ± 9% and 78.8 ± 10%, respectively; single-channel current amplitude was not affected by ethanol. The augmenting effect of ethanol was blocked in the presence of protein kinase C (PKC) inhibitors staurosporine, bisindolylmaleimide, and PKC (19–31) pseudosubstrate inhibitor as well as by AMP-PNP (5′-adenylylimidodiphosphate), a nonhydrolyzable ATP-analogue, but not by the phospholipase C blocker U-73122. Phosphatase inhibitors microcystin-LR and okadaic acid promoted the ethanol effect. The blocking effect was released at higher concentrations of ethanol (100 mm) suggesting a second site of action or a competition between blockers and ethanol. Our results suggest that the effect of ethanol on BK-channels is mediated by PKC stimulation and phosphorylation of the channels which increases channel activity and hence may influence action potentials duration and hormone secretion. Received: 24 July 1996/Revised: 27 December 1996     

Differential effects of eicosapentaenoic acid and oleic acid on lipid synthesis and secretion by HepG2 cells

The effects of eicosapentaenoic acid and oleic acid on lipid synthesis and secretion by HepG2 cells were examined to identify fatty acid specific changes in lipid metabolism that might indicate a basis for the hypolipidemic effect attributed to eicosapentaenoic acid and related n-3 fatty acids. Cellular glycerolipid synthesis, as determined by [3H]glycerol incorporation, increased in a concentration-dependent manner in cells incubated 4 h with either eicosapentaenoic acid or oleic acid at concentrations between 10 and 300 microM. [3H]Glycerol-labeled triglyceride was the principal lipid formed and increased approximately fourfold with the addition of 300 microM oleic acid or eicosapentaenoic acid. Both fatty acids also produced a 20-40% increase in the total cellular triglyceride mass. Although both fatty acids increased triglyceride synthesis to similar extents, eicosapentaenoic acid-treated cells secreted 40% less [3H]glycerol-labeled triglyceride than cells fed oleic acid. Cellular synthesis of [3H]glycerol-labeled phosphatidylethanolamine and phosphatidylcholine was also reduced by 40% and 30%, respectively, in cells given eicosapentaenoic acid versus cells given oleic acid. Similar results were obtained in determinations of radiolabeled oleic acid and eicosapentaenoic acid incorporation. At a fatty acid concentration of 300 microM, incorporation of radiolabeled eicosapentaenoic acid into cellular triglycerides was greater than the incorporation obtained with radiolabeled oleic acid, while the reverse relationship was observed for the formation of phosphatidylcholine from the same fatty acids. Eicosapentaenoic acid is as potent as oleic acid in inducing triglyceride synthesis but eicosapentaenoic acid is a poorer substrate than oleic acid for phospholipid synthesis. The intracellular rise in de novo-synthesized triglyceride in eicosapentaenoic acid-treated cells without corresponding increases in triglyceride secretion suggests that eicosapentaenoic acid is less effective than oleic acid in promoting the transfer of de novo-synthesized triglyceride to nascent very low density lipoproteins.     

The extraction by soil and absorption by plants of applied zinc and cadmium

In five consecutive years lettuce, spinach, spring wheat, endive and maize were grown in pots and the effects of native and soil-applied Zn and Cd on plant Zn and Cd concentrations were studied. The normal interactive pattern was antagonistic, Zn reducing plant Cd uptake, and conversely, but less so. Only in loam soil Zn and Cd were synergistic to some extent, plant Zn uptake increasing with applied Cd.When relating total soil Cd/Zn to plant Cd/Zn separate sets of data could be distinguished for loam and sandy soil, each fitting a straight line. The use of 0.1 M CaCl₂ instead of total extractable soil Cd/Zn makes the two sets of data to coalesce around a single straight line. All crops were found to show a positive linear relationship between 0.1 M CaCl₂-extractable soil Cd/Zn and plant Cd/Zn.