Elevated CO2 effects on carbon and nitrogen cycling in grass/clover turves of a Psammaquent soil

Effects of elevated CO₂ (525 and 700 L L^–1), and a control (350 L L^–1 CO₂), on biochemical properties of a Mollic Psammaquent soil in a well-established pasture of C3 and C4 grasses and clover were investigated with continuously moist turves in growth chambers over four consecutive seasonal temperature regimes from spring to winter inclusive. After a further spring period, half of the turves under 350 and 700 L L^–1 were subjected to summer drying and were then re-wetted before a further autumn period; the remaining turves were kept continuously moist throughout these additional three consecutive seasons. The continuously moist turves were then pulse-labelled with ¹⁴C-CO₂ to follow C pathways in the plant/soil system during 35 days.Growth rates of herbage during the first four seasons averaged 4.6 g m^–2 day^–1 under 700 L L^–1 CO₂ and were about 10% higher than under the other two treatments. Below-ground net productivity at the end of these seasons averaged 465, 800 and 824 g m^–2 in the control, 525 and 700 L L^–1 treatments, respectively.in continuously moist soil, elevated CO₂ had no overall effects on total, extractable or microbial C and N, or invertase activity, but resulted in increased CO₂-C production from soil, and from added herbage during the initial stages of decomposition over 21 days; rates of root decomposition were unaffected. CO₂ produced h^–1 mg^–1 microbial C was about 10% higher in the 700 L L^–1 CO₂ treatment than in the other two treatments. Elevated CO₂ had no clearly defined effects on N availability, or on the net N mineralization of added herbage.In the labelling experiment, relatively more ¹⁴C in the plant/soil system occurred below ground under elevated CO₂, with enhanced turnover of ¹⁴C also being suggested.Drying increased levels of extractable C and organic-N, but decreased mineral-N concentrations; it had no effect on microbial C, but resulted in lowered microbial N in the control only. In soil that had been previously summer-dried, CO₂ production was again higher, but net N mineralization was lower, under elevated CO₂ than in the control after autumn pasture growth.Over the trial period of 422 days, elevated CO₂ generally appears to have had a greater effect on soil C turnover than on soil C pools in this pasture ecosystem.     

Contrasting leaf and ‘ecosystem’ CO2 and H2O exchange in Avena fatua monoculture: Growth at ambient and elevated CO2

Elevated CO₂ (ambient + 35 Pa) increased shoot dry mass production in Avena fatua by 68% at maturity. This increase in shoot biomass was paralleled by an 81% increase in average net CO₂ uptake (A) per unit of leaf area and a 65% increase in average A at the ecosystem level per unit of ground area. Elevated CO₂ also increased ecosystem A per unit of biomass. However, the products of total leaf area and light-saturated leaf A divided by the ground surface area over time appeared to lie on a single response curve for both CO₂ treatments. The approximate slope of the response suggests that the integrated light saturated capacity for leaf photosynthesis is 10-fold greater than the ecosystem rate. Ecosystem respiration (night) per unit of ground area, which includes soil and plant respiration, ranged from-20 (at day 19) to-18 (at day 40) mol m^-2 s^-1 for both elevated and ambient CO₂ Avena. Ecosystem below-ground respiration at the time of seedling emergence was -10 mol m^-2 s^-1, while that occuring after shoot removal at the termination of the experiment ranged from -5 to-6 mol m^-2 s^-1. Hence, no significant differences between elevated and ambient CO₂ treatments were found in any respiration measure on a ground area basis, though ecosystem respiration on a shoot biomass basis was clearly reduced by elevated CO₂. Significant differences existed between leaf and ecosystem water flux. In general, leaf transpiration (E) decreased over the course of the experiment, possibly in response to leaf aging, while ecosystem rates of evapotranspiration (ET) remained constant, probably because falling leaf rates were offset by an increasing total leaf biomass. Transpiration was lower in plants grown at elevated CO₂, though variation was high because of variability in leaf age and ambient light conditions and differences were not significant. In contrast, ecosystem evapotranspiration (ET) was significantly decreased by elevated CO₂ on 5 out of 8 measurement dates. Photosynthetic water use efficiencies (A/E at the leaf level, A/ET at the ecosystem level) were increased by elevated CO₂. Increases were due to both increased A at leaf and ecosystem level and decreased leaf E and ecosystem ET.     

Spatial and temporal variation in soil CO2 efflux in an old-growth neotropical rain forest, La Selva, Costa Rica

Our objectives were to quantify and compare soil CO₂ efflux of two dominant soil types in an old-growth neotropical rain forest in the Atlantic zone of Costa Rica, and to evaluate the control of environmental factors on CO₂ release. We measured soil CO₂ efflux from eight permanent soil chambers on six Oxisol sites. Three sites were developed on old river terraces (old alluvium) and the other three were developed on old lava flows (residual). At the same time we measured soil CO₂ concentrations, soil water content and soil temperature at various depths in 6 soil shafts (3 m deep). Between old alluvium sites, the two-year average CO₂ flux rates ranged from 117.3 to 128.9 mg C m^–2 h^–1. Significantly higher soil CO₂ flux occurred on the residual sites (141.1 to 184.2 mg C m^–2 h^–1). Spatial differences in CO₂ efflux were related to fine root biomass, soil carbon and phosphorus concentration but also to soil water content. Spatial variability in CO₂ storage was high and the amount of CO₂ stored in the upper and lower soil profile was different between old alluvial and residual sites. The major factor identified for explaining temporal variations in soil CO₂ efflux was soil water content. During periods of high soil water content CO₂ emission decreased, probably due to lower diffusion and CO₂ production rates. During the 2-year study period inter-annual variation in soil CO₂ efflux was not detected.     

Interrelationships Between Nitrogen Supply and Photosynthetic Parameters in Vicia faba L.

We determined for Vicia faba L the influence of nitrogen uptake and accumulation on the values of photon saturated net photosynthetic rate (P _Nmax), quantum yield efficiency (), intercellular CO₂ concentration (C _i), and carboxylation efficiency (C _e). As leaf nitrogen content (N_L) increased, the converged onto a maximum asymptotic value of 0.0664±0.0049 mol(CO₂) mol(quantum)^–1. Also, as N_L increased the C _i value fell to an asymptotic minimum of 115.80±1.59 mol mol^–1, and C _e converged onto a maximum asymptotic value of 1.645±0.054 mol(CO₂) m^–2 s^–1 Pa^–1 and declined to zero at a N_L-intercept equal to 0.596±0.096 g(N) m^–2. fell to zero for an N_L-intercept of 0.660±0.052 g(N) m^–2. As N_L increased, the value of P _Nmax converged onto a maximum asymptotic value of 33.400±2.563 mol(CO₂) m^–2 s^–1. P _N fell to zero for an N_L-intercept of 0.710±0.035 g(N) m^–2. Under variable daily meteorological conditions the values for N_L, specific leaf area (_L), root mass fraction (R_f), P _Nmax, and remained constant for a given N supply. A monotonic decline in the steady-state value of R_f occurred with increasing N supply. _L increased with increasing N supply or with increasing N_L.     

Somatic embryogenesis in callus cultures of Rosa hybrida L. cv. Landora

Callus was initiated from immature leaf and stem segments of rose (Rosa hybrida cv. Landora) and subcultured every four weeks on a basal medium of half-strength Murashige & Skoog (1962) salts plus 30 g l^-1 sucrose (1/2 MS) and supplemented with 2.2 M BA, 5.4 M NAA and 2.2–9.0 M 2,4-D. Embryogenic callus and subsequently somatic embryos were obtained from 8-week-old callus culture on 1/2 MS+2.2 M BA+0.05 M NAA+0.3 M GA₃+200–800 mg l^-1 L-proline. Long-term cultures were established and maintained for up to 16 months by repeated subculture of embryogenic callus on L-proline deficient medium. About 12% of cotyledonary stage embryos taken from cultures cold-stored at 8±1°C for 4 days germinated on 1/2 MS+2.2 M BA+0.3 M GA₃+24.7 M adenine sulphate.Abbreviations BA benzyladenine - NAA -naphthaleneacetic acid - 2,4-D 2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid     

Quantification of soil carbon inputs under elevated CO2: C3 plants in a C4 soil

The objective of this investigation was to quantify the differences in soil carbon stores after exposure of birch seedlings (Betula pendula Roth.) over one growing season to ambient and elevated carbon dioxide concentrations. One-year-old seedling of birch were transplanted to pots containing C₄ soil derived from beneath a maize crop, and placed in ambient (350 L L^–1) and elevated (600 L L^–1) plots in a free-air carbon dioxide enrichment (FACE) experiment. After 186 days the plants and soils were destructively sampled, and analysed for differences in root and stem biomass, total plant tissue and soil C contents and ¹³C values. The trees showed a significant increase (+50%) in root biomass, but stem and leaf biomasses were not significantly affected by treatment. C isotope analyses of leaves and fine roots showed that the isotopic signal from the ambient and elevated CO₂ supply was sufficiently distinct from that of the C₄ soil to enable quantification of net root C input to the soil under both ambient and elevated CO₂. After 186 days, the pots under ambient conditions contained 3.5 g of C as intact root material, and had gained an additional 0.6 g C added to the soil through root exudation/turnover; comparable figures for the pots under elevated CO₂ were 5.9 g C and 1.5 g C, respectively. These data confirm the importance of soils as an enhanced sink for C under elevated atmospheric CO₂ concentrations. We propose the use of C₄ soils in elevated CO₂ experiments as an important technique for the quantification of root net C inputs under both ambient and elevated CO₂ treatments.     

A role for G-proteins in the epidermal growth factor stimulation of phospholipase A2 in rat kidney mesangial cells

We have previously demonstrated phospholipase C (PLC) independent activation of phospholipase A₂(PLA₂) by epidermal growth factor (EGF) in glomerular mesangial cells in culture. In the current study using glass beads to permeabilize [³H]- or [¹⁴C]-arachidonate labelled mesangial cells we demonstrate that guanine nucleotides modulate the EGF-mediated stimulation of arachidonic acid release (75% inhibition with 100 M GDPS and 108% augmentation with 100 M GTPS). GTPS alone stimulated both the release of free arachidonic acid and production of diacylglycerol (DAG), while EGF itself neither stimulated DAG nor augmented the DAG response to GTPS. These findings suggest the intermediacy of a G-protein in PLC-independent stimulation of PLA₂ by a growth factor, and provide a model system for determining the relationship between G-protein intermediacy and the intrinsic tyrosine kinase activity of the growth factor receptor.Abbreviations EGF Epidermal Growth Factor - PLC phospholipase C - PLA₂ phospholipase A₂ - DAG Diacylglycerol - NEFA non-esterified fatty acid - GTPS guanosine-5-0-[3-thio]triphosphate - GDP\S guanosine-5-0-[2-thio]diphosphate     

Carbon-isotope discrimination by leaves of Flaveria species exhibiting different amounts of C3-and C4-cycle co-function

Carbon-isotope ratios were examined as ¹³C values in several C₃, C₄, and C₃–C₄ Flaveria species, and compared to predicted ¹³C, values generated from theoretical models. The measured ¹³C values were within 4 of those predicted from the models. The models were used to identify factors that contribute to C₃-like ¹³C values in C₃–C₄ species that exhibit considerable C₄-cycle activity. Two of the factors contributing to C₃-like ¹³C values are high CO₂ leakiness from the C₄ pathway and pi/pa values that were higher than C₄ congeners. A marked break occurred in the relationship between the percentage of atmospheric CO₂ assimilated through the C₄ cycle and the ¹³C value. Below 50% C₄-cycle assimialtion there was no significant relationship between the variables, but above 50% the ¹³C values became less negative. These results demonstrate that the level of C₄-cycle expression can increase from, 0 to 50% with little integration of carbon transfer from the C₄ to the C₃ cycle. As expression increaces above 50%, however, increased integration of C₃- and C₄-cycle co-function occurs.Abbreviations and symbols RuBP carboxylase ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) - PEP carboxylase phosphoenolpyruvate carboxylase (EC 4.1.1.31) - pa atmospheric CO₂ partial pressure - pi intercellular CO₂ partial pressure - isotope ratio - quantum yield for CO₂ uptake     

Light dependence of quantum yields of Photosystem II and CO2 fixation in C3 and C4 plants

The light dependence of quantum yields of Photosystem II (_II) and of CO₂ fixation were determined in C₃ and C₄ plants under atmospheric conditions where photorespiration was minimal. Calculations were made of the apparent quantum yield for CO₂ fixation by dividing the measured rate of photosynthesis by the absorbed light [A/I=_CO2 and of the true quantum yield by dividing the estimated true rate of photosynthesis by absorbed light [(A+R_l)/I_a=_CO2·], where R_L is the rate of respiration in the light. The dependence of the _II/_CO2 and _II/_CO2 ^* ratios on light intensity was then evaluated. In both C₃ and C₄ plants there was little change in the ratio of _II/_CO2 at light intensities equivalent to 10–100% of full sunlight, whereas there was a dramatic increase in the ratio at lower light intensities. Changes in the ratio of _II/_CO2 can occur because respiratory losses are not accounted for, due to changes in the partitioning of energy between photosystems or changes in the relationship between PS II activity and CO₂ fixation. The apparent decrease in efficiency of utilization of energy derived from PS II for CO₂ fixation under low light intensity may be due to respiratory loss of CO₂. Using dark respiration as an estimate of R_L, the calculated _II/_CO2 ^* ratio was nearly constant from full sunlight down to approx 5% of full sunlight, which suggests a strong linkage between the true rate of CO₂ fixation and PS II activity under varying light intensity. Measurements of photosynthesis rates and _II were made by illuminating upper versus lower leaf surfaces of representative C₃ and C₄ monocots and dicots. With the monocots, the rate of photosynthesis and the ratio of _II/_CO2 exhibited a very similar patterns with leaves illuminated from the adaxial versus the abaxial surface, which may be due to uniformity in anatomy and lack of differences in light acclimation between the two surfaces. With dicots, the abaxial surface had both lower rates of photosynthesis and lower _II values than the adaxial surface which may be due to differences in anatomy (spongy versus palisade mesophyll cells) and/or light acclimation between the two surfaces. However, in each species the response of _II/_CO2 to varying light intensity was similar between the two surfaces, indicating a comparable linkage between PS II activity and CO₂ fixation.Abbreviations A measured rate of CO₂ assimilation - A+R_L true rate of CO₂ assimilation; e - CO₂ estimate of electrons transported through PSII per CO₂ fixed by RuBP carboxylase - f fraction of light absorbed by Photosystem II - F'_m yield of PSII chlorophyll fluorescence due to a saturating flash of white light under steady-state photosynthesis - F_s variable yield of fluorescence under steady-state photosynthesis; PPFD-photosynthetic photon flux density - I_a absorbed PPFD - PS II Photosystem II - R_d rate of respiration in the dark - R_I rate of respiration in the light estimated from measurement of R_d or from analysis of quantum yields - apparent quantum yield of CO₂ assimilation under a given condition (A/absorbed PPFD) - true quantum yield of CO₂ assimilation under a given condition [(A+R_L)/(absorbed PPFD)] - quantum yield for photosynthetic O₂ evolution - electrons transported via PS II per quantum absorbed by PS II Supported by USDA Competitive Grant 90-37280-5706.     

Contribution of methanol to the production of methane and its <Superscript>13</Superscript>C-isotopic signature in anoxic rice field soil

Conversion of methanol to CH₄ has a large isotope effect so that a small contribution of methanol-dependent CH₄ production may decrease the ¹³CH₄ of total CH₄ production. Therefore, we investigated the role of methanol for CH₄ production. Methanol was not detectable above 10 M in anoxic methanogenic rice field soil. Nevertheless, addition of ¹³C-labeled methanol (99% enriched) resulted in immediate accumulation of ¹³CH₄. Addition of 0.1 M ¹³C-methanol resulted in increase of the ¹³CH₄ from –47 to –6 within 2 h, followed by a slow decrease. Addition of 1 M ¹³C-methanol increased ¹³CH₄ to +500 within 4 h, whereas 10 M increased ¹³CH₄ to +2500 and continued to increase. These results indicate that the methanol concentrations in situ, which diluted the ¹³C-methanol added, were 0.1 M and that the turnover of methanol contributed only about 2% to total CH₄ production at 0.1 M. However, contribution increased up to 5 and 17% when 1 and 10 M methanol were added, respectively. Anoxic rice soil that was incubated at different temperatures between 10 and 37 °C exhibited maximally 2–6% methanol-dependent methanogenesis about 1–2 h after addition of 1 M ¹³C-methanol. Only at 50 °C, contribution of methanol to CH₄ production reached a maximum of 10%. After longer (7–10 h) incubation, however, contribution generally was only 2–4%. Methanol accumulated in the soil when CH₄ production was inhibited by chloroform. However, the accumulated methanol accounted for only up to 0.7 and 1.2% of total CH₄ production at 37 and 50 °C, respectively. Collectively, our results show that methanol-dependent methanogenesis was operating in anoxic rice field soil but contributed only marginally to total CH₄ production and the isotope effect observed at both low and high temperature.     

Mineral catalysis of the formation of dimers of 5′-AMP in aqueous solution: The possible role of montmorillonite clays in the prebiotic synthesis of RNA

The reaction of the 5-AMP with water soluble carbodiimide (EDAC) in the presence of Na⁺-montmorillonite 22A results in the formation of 2,5-(pA)₂ (18.9%), 3,5-(pA)₂ (11%), and AppA (4.8%). When poly(U) is used in place of the clay the product yields are 2,5-(pA)₂ (15.5%), 3,5-(pA)₂ (3.7%) and AppA (14.9%). The 3,5-cyclic dinucleotide, 3,5-c(pA)₂, is also formed when poly(U) is used. AppA is the principal reaction product when neither clay nor poly(U) is present in the reaction mixture. Products which contain the phophodiester bond are formed at different ionic strengths, pH and temperatures using Na⁺-montmorillonite. Phosphodiester bond formation was not observed when Cu²⁺-montmorillonite was used or when DISN was used in the place of EDAC. The extent catalysis of phophodiester bond formation varied with the particular clay mineral used. Those Na⁺-clays which bind 5-AMP more strongly are better catalysts. Cu²⁺-montmorillonite, which binds 5-AMP strongly, exhibits no catalytic activity.     

The α2 cDNA sequence of human haptoglobin carries a bacterial promoter functionalin vivo

Various constructions of human haptoglobin (Hp) cDNA coding either for the complete ^2FS precursor protein or only for the subunit have been placed under the control of the P_R promoter in the bacterial expression vector pCQV2 (Queen, 1983). In addition to the expected 45,000 dalton polypeptide synthesized after induction of the P_R promoter, the complete ^2FS constructions constitutively express a smaller polypeptide of 30,000 dalton corresponding to a truncated Hp protein. Computer analysis of the HpcDNA revealed the presence of two strong potential bacterial promoters (²P_F and ²P_S) located in the duplicated ^2FS sequence. Both Hp promoter signals are followed by potential mRNA start sites and ribosome binding sites at a compatible distance from initiation codons. In addition, the Hp² cDNA sequence, when fused upstream to the cDNA coding for ¹-antitrypsin, constitutively promotesin vivo the efficient expression of an hybrid protein specifically recognized by antibodies raised against ¹-antitrypsin or haptoglobin.     

Effect of the triacontanol formulation ‘Miraculan’ on photosynthesis,growth, nutrient uptake,and essential oil yield of Lemongrass (Cymbopogon flexuosus) Steud. Watts

The influence of different foliar applications of the triacontanol (Tria.) based plant grow regulator-Miraculan, on growth, CO₂ exchange and essential oil accumulation in Lemongrass (Cymbopogon flexuosus L.) Steud. Watts. was studied in glass-house conditions. The yield components, viz., plant height, tillers per plant, biomass yield, accumulation of essential oil, net CO₂ exchange and transpiration rates increased with Miraculan treatment of 0.4 g/ml compared to the untreated control, but the number of leaves per tiller remained unaffected. Application of Miraculan at 0.4 g/ml increased micronutrient uptake, total chlorophyll and citral content but decreased chlorophyll a/b ratio and stomatal resistance. Increase in shoot biomass, photosynthesis and chlorophyll were significantly correlated with essential oil content.     

Partial mispairing and crossing-over between β0 and δ genes as the origin of the δ β0 thalassemia gene

Summary Two double heterozygous ⁰/⁰ thalassemic sibs of Mexican descent were studied. The father had a ⁰/⁰ genotype, while the mother, one sib and several maternal relatives were ⁰/⁰ heterozygotes. Parental consanguinity and an apparently low frequency of thalassemia among Mexicans suggested a possible common origin of both ⁰ and ⁰ genes. A hypothesis to explain such a possibility is proposed on the basis of a partial mispairing between ⁰ and genes followed by a crossing-over which would results in a ⁰ recombinant gene. This hypothesis could also be extended to explain the 22 gluala, 22 alaglu and 116 arghis Hb variants as recombinants from double crossing-over between and mispaired genes for which the name interstitial-Lepore is proposed.     

The effect of fumonisin B1 on developing chick embryos: correlation between de novo sphingolipid biosynthesis and gross morphological changes

Fumonisins, mycotoxins produced byFusarium moniliforme and a number of other fungi, are potent inhibitors of the sphinganine-N-acyltransferase, a key enzyme of sphingolipid biosynthesis, and cause neuronal degeneration, liver and renal toxicity, cancer and other injury to animals.In this study we investigated the effect of fumonisin B₁ on the sphingolipids of developing chick embryos. After yolk sac injection of fumonisin B₁ a concentration and time dependent increase of the sphinganine-over-sphingosine ratio of the embryos could be demonstrated. Studies were done to evaluate the effect of fumonisin B₁ on the glycosphingolipid pattern of the chick embryos. In the presence of 72 µg fumonisin B₁ per egg the incorporation of [¹⁴C]galactose and of [¹⁴C]serine into embryonic glycosphingolipids was reduced by about 70%, although the mass of glycosphingolipids was not affected by the toxin. However, a reduction of the wet weight of the treated embryos was observed. Additionally, histological examinations of whole embryo sections of control and fumonisin B₁ treated embryos are presented. Fumonisin B₁ caused haemorrhages under the skin as well as in the liver of treated embyros. A close correlation between disruption of sphingoid metabolism and light microscopic detectable tissue lesions could be observed.Abbreviations Cer ceramide (N-acylsphingosine) - FB₁ fumonisin B₁ - GM3 NeuAc23Gal14Glc11Cer - GD3 NeuAc28NeuAc23Gal14Glc11Cer - GD1a NeuAc23Gal13GalNAc14(NeuAc23)Gal14Glc11Cer - GT1b NeuAc23Gal13GalNAc14(NeuAc28NeuAc23) Gal14Glc11Cer - HPLC high pressure liquid chromatography - PBS phosphate buffered saline - PDMP 1-phenyl-2-dodecanoylamino-3-morpholino-1-propanol - Sa sphinganine - So sphingosine - Sa/So sphinganine-over-sphingosine - TLC thin layer chromatography - Tris Tris(hydroxymethyl)aminomethan Dedicated to Dr Sen-itiroh Hakomori in celebration of his 65th birthday.     

Reciprocal Innervation between Serotonergic and GABAergic Neurons in Raphe Nuclei of the Rat

Midbrain slices containing the dorsal and medial raphe nuclei were prepared from rat brain in order to study serotonergic-GABAergic interaction. The slices were loaded with either [³H] serotonin or [³H]GABA, superfused and the electrically induced efflux of radioactivity was determined. The GABA_A receptor agonist muscimol (3 to 30 M) and the GABA_B receptor agonist baclofen (30 and 100 M) inhibited [³H]serotonin and [³H]GABA release. These effects of muscimol were reversed by the GABA_A antagonists bicuculline (100 M). The GABA_B antagonist phaclofen (100 M) also antagonized the baclofen-induced inhibition of [³H]serotonin and [³H]GABA release. Phaclofen by itself increased [³H]serotonin release but it did not alter [³H]GABA overflow. Muscimol (10 M) and baclofen (100 M) also inhibited [³H]serotonin release after depletion of GABAergic neurons by isoniazid pretreatment. These findings indicate the presence of postsynaptic GABA_A and GABA_B receptors located on serotonergic neurons. The 5-HT_1A receptor agonist 8-OH-DPAT (0.01 to 1 M) and the 5-HT_1B receptor agonist CGS-12066A (0.01 to 1 M) inhibited the electrically stimulated [³H]serotonin and [³H]GABA release. The 5-HT_1A antagonist WAY-100135 (1 M) was without effect on [³H]serotonin and [³H]GABA efflux by itself but it reversed the 8-OH-DPAT-induced transmitter release inhibition. During KCl (22 mM)-induced depolarization, tetrodotoxin (1 M) did not alter the inhibitory effect of CGS-12066A (1 M) on [³H]GABA release, it did blocked, however, the ability of 8-OH-DPAT (1 M) to reduce [³H]GABA efflux. After depletion of raphe serotonin neurons by p-chlorophenylalanine pretreatment, CGS-12066A (1 M) still inhibited [³H]GABA release whereas in serotonin-depleted slices, 8-OH-DPAT (1 M) was without effect on the release. We conclude that reciprocal influence exists between serotonergic projection neurons and the GABAergic interneurons or afferents in the raphe nuclei and these interactions may be mediated by 5-HT_1A/B and GABA_A/B receptors. Both synaptic and non-synaptic neurotransmission may be operative in the 5-HTergic-GABAergic reciprocal interaction which may serve as a local tuning in the neural connection between cerebral cortex and midbrain raphe nuclei.     

Autotrophic carbon sources for heterotrophic bacterioplankton in a floodplain lake of central Amazon

The relative contribution of autotrophic carbon sources (aquatic macrophytes, flooded forest, phytoplankton) for heterotrophic bacterioplankton was evaluated in a floodplain lake of the Central Amazon. Stable carbon isotopes (¹³C) were used as tracers. Values of ¹³C of different autotrophic sources were compared to those of dissolved organic carbon (DOC) and those of bacterially produced CO₂.The percentage of carbon derived from C₄ macrophytes for bacterially produced CO₂ was the highest, on average 89%. The average ¹³C value of CO₂ from bacterial respiration was –18.5 ± 3.3. Considering a fractionation of CO₂ of 3 by bacterial respiration, ¹³C value was –15.5, near C₄ macrophyte ¹³C value (–13.1).The average value of total DOC ¹³C was –26.8 ± 2.4. The percentage of C₄ macrophytes carbon for total DOC was on average 17%. Considering that bacteria consume mainly carbon from macrophytes, the dominance of C₃ plants for total DOC probably reflects a faster consumption of the former source, rather than a major contribution of the latter source.Heterotrophic bacterioplankton in the floodplain may be an important link in the aquatic food web, transferring the carbon from C₄ macrophytes to the consumers.     

CO2 gas exchange of benthic microalgae during exposure to air: a technique for the rapid assessment of primary production

A method of measuring CO₂gas exchange (caused, for example, by microalgal photosynthesis on emersed tidal mudflats) using open flow IR gas analyzers is described. The analyzers are integrated in a conventional portable photosynthesis system (LI-6400, LI-COR, Nebraska, USA), which allows manipulation and automatic recording of environmental parameters at the field site. Special bottomless measuring chambers are placed directly on the surface sediment. Measurements are performed under natural light conditions and ambient CO₂concentrations, as well as under different CO₂concentrations in air, and various PAR radiation levels produced by a LED light source built into one of the measurement chambers. First results from tidal channel banks in a north Brazilian mangrove system at Bragança (Pará, Brazil) under controlled conditions show a marked response of CO₂assimilation to CO₂concentration and to irradiance. Photosynthesis at 100molmol^–1CO₂in air in one sample of a well-developed algal mat was saturated at 309mol photons m^–2s^–1, but increased with increasing ambient CO₂concentrations (350 and 1000mol mol^–1CO₂) in the measuring chamber. Net CO₂assimilation was 0.8mol CO₂m^–2s^–1at 100mol mol^–1CO₂, 5.9mol CO₂m^–2s^–1at 350mol mol^–1CO₂and 9.8mol CO₂m^–2s^–1at 1000mol mol^–1CO₂. Compensation irradiance decreased and apparent photon yield increased with ambient CO₂concentration. Measurements under natural conditions resulted in a quick response of CO₂exchange rates when light conditions changed. We recommend the measuring system for rapid estimations of benthic primary production and as a valuable field research tool in connection with certain ecophysiological aspects under changing environmental conditions.     

Kinetics of growth and lactic acid production in continuous and batch culture

Summary In a lactic acid fermentation by Streptococcus faecalis, the specific consumption rate of glucose (v) and the specific production rate of lactic acid () were represented by the following simple equations as functions of the specific growth rate (): 1/=(1/) + 1/ = (1/) + By use of data from a batch culture, these two equations were derived from enzyme kinetics of the product inhibition. These equations were successfully applied to the results of batch culture and chemostat culture. In addition, calculation of ATP yield by these equations agreed with the experimental results better than the conventional Leudeking-Piret type equation, which includes two terms associated with growth and not with growth. Correspondence to: H. Ohara     

Temperate and virulent forms of phage theta attacking Bacillus licheniformis

Summary Clear-plaque phage _c, attacking bacitracin-producing strains of B. licheniformis, yields spontaneous temperate mutants at high frequency; the temperate mutants fall into several classes phenotypically different in plaque morphology and properties of lysogenised bacteria. The most common phenotype ₃ has DNA restriction fragment patterns identical with those of the parent _c; some less common temperate forms, i.e. ₁ and ₂, produce different restriction fragment patterns, sugesting that a part of the original _c DNA has been reorganized or replaced by some foreign genetic material. The changed fragment pattern remains stable upon subsequent passaging of the phage or of the lysogenic bacteria. Neither class of temperate phage mutants gives clearplaque revertants at measurable frequency. Lysogenisation of bacteria with any class of temperate phage confers immunity to all temperate forms and to _c; virulent mutants _vir, which plate with 100% efficiency on lysogens for ₁ and ₂ but not for ₃, occur in stocks of _c at a frequency of 10^–7. The mutation from _c to _vir is not accompanied by any change of the restriction fragment patterns of DNA.