Tissue culture ofKarwinskia humboldtiana—a plant producing toxins with antitumoural effects

Isolated embryos ofKarwinskia humboldtiana were cultured in vitro. The growth of embryos and development to plantlets on woody plant medium supplemented with indole-3-acetic acid 6.10^-2 mol l^–1, gibberellic acid (GA₃) 3.10^-2 mol l^–1, and 6-benzylaminopurine (BA) 2 mol l^–1 was obtained. Multiplication of shoots and rooting of excised shoots has been achieved. Callus formation on modified Murashige-Skoog medium supplemented with 1-naphthaleneacetic acid 10 mol l^–1, GA₃ 14 mol l^–1, and kinetin 5 mol l^–1 on hypocotyls, or on root cultures on medium supplemented with 2.4-dichlorophenoxyacetic acid 10 mol l^–1 and BA 10 mol l^–1 was induced.Abbreviations BA 6-benzylaminopurine - 2,4-d 2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid - IAA indole-3-acetic acid - NAA 1-naphthaleneacetic acid - TEM transmission electron microscopy     

Influence of nitrogen on the behaviour of nickel in wheat

A glasshouse experiment was conducted to study the effect of Ni on the growth and nutrients concentration in wheat (Triticum aestivum Cv. WH 291) in the presence and absence of applied N as urea. Responses to N application were observed up to 120 g N g^–1 soil. No response to Ni was observed in the dry matter yield of wheat tops (leaves + stem) in the absence of applied N while in the presence of applied N, significant yield increases were obtained at 12.5g Ni g^–1 soil. Nickel was not toxic to wheat up to 50g Ni g^–1 soil in the presence of 120g N g^–1 soil. Nitrogen and Ni concentration in wheat tops and roots increased with increasing levels of applied N and Ni, respectively. Applied Ni had an antagonistic effect on N concentration. Similarly, N reduced the Ni concentration in the wheat tissues. Positive growth responses to Ni were associated with 22 and 15g Ni g^–1 in wheat tops, in the presence of applied N at 60 and 120g N g^–1 soil, while Ni toxicity was associated with 63, 92.5 and 112.5g Ni g^–1 in wheat tops, in the absence and presence of applied N at 60 and 120g N g^–1 soil, respectively.     

Stimulation of growth and phospholipase A2 by the peptides mastoparan and melittin and by the auxin 2,4-dichlorophenoxyacetic acid

The peptide mastoparan from wasp venom and the peptide melittin from bee venom stimulated growth in etiolated zucchini (Cucurbita pepo L.) hypocotyls. Both peptides were only effective in hypocotyls with abraded cuticles. At concentrations of 2 g ml^–1 peptide growth was stimulated 72% by mastoparan and 50% by melittin after 2 h as compared to the controls. Mastoparan (5 g ml^–1), melittin (10 g l^–1) and 2,4-dichlorophenoxyacetic acid (5×10^–4 M) stimulated accumulation of ¹⁴C-choline-labeled lysophosphatidylcholine in less than 10 min in cultured soybean cells (Glycine max L.), all to about the same extent. The effects of these peptides are among the first to be reported on plant cells and may be related to important events coupled to growth stimulation.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid     

Fabrication of Stable Packed Capillary Reversed-Phase Columns for Protein Structural Analysis

Capillary column (320-m ID) liquid chromatography is an essential tool for the separation and concentration of low-picomole amounts of proteins and peptides for mass-spectrometric based structural analysis. We describe a detailed procedure for the fabrication of stable and efficient 50- to 180-m ID polyimide fused-silica columns. Columns were packed by conventional slurry packing with reversed-phase silica-based supports followed by column bed consolidation with acetonitrile and sonication. PVDF membrane or internal fused-silica particles were employed for column end-frit construction. The ability of these columns to withstand high back pressures (300–400 bar) enabled their use for rapid chromatography (>3400 cm/hr; i.e., 40 l/min for 200-m ID columns) and the loading of large sample volumes (up to 500 l). The accurate low flow rates (0.4–4.0 l/min) and precise gradient formation necessary to operate these columns were achieved by a simple modification of conventional HPLC systems [Moritz et al. (1992), J. Chromatogr. 599, 119–130]. Column performance was evaluated for ability to resolve low-fmol amounts of all components of a mixture of PTH-amino acids and to separate peptides for on-line LC/MS analysis of peptide mixtures derived from in situ digestion of 2-DE resolved protein spots.     

Contribution of flow cytometry to estimate picoplankton biomass in estuarine systems

Picoplankton (plankton 3 m) biomass was determined by flow cytometry in three European estuarine systems (Krka Estuary in Croatia, Rhône Delta in France, and Lena Delta and Laptev Sea in Russia). The size of natural phytoplankton groups was obtained by a calibration curve, with different picoplankton's strains (from 1.6 to 3.4 m), measured by a Coulter counter (size) and a flow cytometer (light-scattering). Two natural groups of picoplankton were identified by flow cytometry in the three systems: Synechococcus sp and picoeukaryotes. Picoplankton cells abundance ranged between: 2800 and 42000, 5000 and 37000, 1000 and 50000 cells ml^–1 in the Krka estuary, in the Rhône delta and in the Lena-Laptev system, respectively. In the Krka estuary, picoplankton biomass ranges between 11 and 68 gC l^–1. It can make up as much as 88% of the total photosynthetic plankton population and 50% of total organic particulate carbon. Picoplankton biomass was greater in the summer than in the autumn. At the halocline layer this biomass can attempt ca. 390 gC l^–1during the summer cruise. In the Rhône delta, a lower picoplankton biomass (6–39 gC l^–1) was observed at the end of the winter. These biomass represented between 0.4 and 22% of the particulate organic carbon, which could reach 71% of the total photosynthetic plankton biomass at the marine station. In the Lena-Laptev system, picoplankton biomass varied between 6 and 56 gC l^–1 in surface waters. Picoplankton biomass decreased with depth, but picoeukaryotes were still observed in deep samples (20, 30 m) in the Laptev Sea, showing a considerable autotrophic activity in spite of low temperatures (0–1 °C). Although the widely dispersed estuary geographic distribution and their different estuarine characteristics, the data point out that these small organisms can also play an important role in the transfer of organic carbon from rivers to oceans and that flow cytometry can be able to detect these small cells in turbid systems.     

Development of an L6 myoblast in vitro model of moniliformin toxicosis

L6 myoblasts were used as an in vitro model to investigate the role of moniliformin and its interaction with monensin in turkey knockdown syndrome and sudden death syndromes in poultry. Cell viability and microscopic and ultrastructural alterations noted in L6 myoblasts cultured in the presence of moniliformin (0.0–0.3 g/l) were compared to those observed in parallel cultures also containing one of the following compounds: selenium (0–0.004 ng/l), thiamine (0–0.3 g/l), or pyruvate (0–0.46 g/l). Marked dilation of the RER, membranous whorls, glycogen deposition, membrane-bound cytoplasmic inclusions and necrosis were observed in myoblasts exposed to 0.03/2-0.30 g moniliformin/l medium. Supplementation of medium with thiamine and pyruvate, or selenium, provided significant protection to cells exposed to 0.0–0.3 g/l or 0.0–0.15 g moniliformin/l, respectively. Dose-dependent differences in protein and ATP production were not detected. Myoblasts grown in medium containing 0–0.15 g moniliformin/l and 7.5–50.0 M A23187, beauvericin or monensin had degrees of cytotoxicity similar to parallel cultures receiving only an ionophore. L6 myoblasts were a useful model of moniliformin toxicosis. The findings of this study suggest cytotoxicity due to moniliformin in L6 myoblasts may be due in part to oxidative damage and altered pyruvate metabolism, and that moniliformin does not predispose myoblasts to ionophore toxicosis. This study supports the results of in vivo investigations in poultry that moniliformin and monensin do not act synergistically to induce knockdown or monensin toxicosis.     

Ultrastructure of the “statocysts” inProtodrilus species (Polychaeta): Reconstruction of the cellular organization with morphometric data from receptor cells

Summary The statocysts inProtodrilus ciliatus, P. oculifer, P. haurakiensis andP. helgolandicus are situated in the prostomium anterior to the palps and have been investigated by electron microscopy. The sensory organs were reconstructed from serial sections, volumes were calculated from areas of consecutive section profiles, and additional data on surface area of distal receptor elements have been determined. In spite of variations in size (diameter 8–20 m) their structure is nearly identical. The organs consist of one cup-shaped supportive cell, one large bi- or multiciliated sensory cell and two small uni- or biciliated sensory cells forming an extracellular cavity. This cavity is completely filled with microvillus-like or paracrystalline structures and there are no signs of statoliths composed of extracellular material. The most striking feature is the occurrence of paracrystals made up of undulating ciliary membranes extending from the large sensory cell and occupying 75–90% of the cavity inP. ciliatus, P. oculifer andP. haurakiensis. The remaining space is filled with microvilli or dendritic processes of the sensory cells. InP. helgolandicus the ciliary paracrystals are almost completely replaced by microvillus-like branches of cilia of the corresponding sensory cell. Paracrystals fill less than 10% of the cavity and are formed of flattened membranes. These sensory organs enclose large surface areas of membranes (15,000–38,000 m²). The surface areas of the paracrystals composed of undulating membranes is almost identical to that of densely arranged arrays of microvilli (about 25 m² per m³). These sensory organs are so different from all known statocysts that it is likely that they have another function. Their greatest structural correspondence is to light-receptive organs, especially in the structure and arrangement of microvilli. The role the paracrystals play is discussed: they might bear photopigments or simply represent a lens — a transparent, refractile and crystalline structure. These sensory organs are completely different from pigmented ocelli and phaosomes occurring in some protodrilids and represent a type of sensory organ thus far undescribed in polychaetes.     

Architecture of the media of the arterial vessels in the dog brain: A scanning electron-microscopic study

Summary The architecture of the media of arterial vessels in dog brain was investigated using scanning electron microscopy. The arrangement and shape of the circularly-oriented smooth muscle cells varied with vessel diameter: The arteries (>100 m in diameter) had 4–10 layers of spindle-shaped smooth muscle cells; the muscular arterioles (30–100 m), 2–3 layers of spindle-shaped smooth muscle cells; the terminal arterioles (10–30 m), a compact layer of spindle-shaped smooth muscle cells with more dominant nodular or rod-like processes and thin lateral processes; and the precapillary arterioles (5–15 m), a less compact layer of branched smooth muscle cells.Longitudinally-oriented muscles were observed in the medio-adventitial border. The distribution and arrangement of these muscles varied with vessel size: in the large arteries (> 300 m in diameter), at the branching sites only; in the small arteries (100–300 m), at both the branching and non-branching sites; in the muscular arterioles, at both the branching and non-branching sites in a reticular arrangement with some muscle cells having an asteroid appearance; in the terminal aterioles, only asteroid-like muscle cells were found at the branching and non-branching sites.     

Five new species of coccidia (Apicomplexa: Eimeriidae) from Madagascan chameleons (Sauria: Chamaeleonidae)

Coprological examination of 19 Madagascan chameleons of the genera Furcifer and Brookesia revealed the presence of five new coccidian species. Isospora brygooi n. sp. from Furcifer pardalis has spherical to subspherical oöcysts with a slightly pitted wall, 20.7 (17–24.5) × 19.3 (16–23) m and broadly ellipsoidal sporocysts, 12.2 (11.5–13) × 8.1 (8–8.5) m, with Stieda and substieda bodies. Oöcysts of Eimeria glawi n. sp. from Furcifer pardalis are cylindrical to ellipsoidal, 27.7 (26–29.5) × 18.4 (17–19) m, with ellipsoidal sporocysts, 7.3 (6.5–8) × 5.2 (5–5.5) m. E. vencesi n. sp. described from F. pardalis has spherical to subspherical oöcysts, 14.3 (13–15.5) × 13.0 (12–13) m, with small granules, one to three globular polar granules and ellipsoidal sporocysts, 7.3 (6.5–8) × 5.2 (5–5.5) m. E. worthi n. sp., described from Furcifer oustaleti has spherical oöcysts, 17.9 (17.5–19.0) × 15.0 (14.5–16.0) m without a polar granule and ellipsoidal to cylindroidal sporocysts, 8.2 (7.0–9.5) × 5.8 (5.0–6.5) m. Oöcysts of E. brookesiae n. sp. from Brookesia decaryi are cylindrical, 25.6 (23–27) × 15.0 (13–16) m with ellipsoidal sporocysts, 10.1 (9–11) × 6.9 (6–7) m. Endogenous development of E. vencesi is confined to the intestine, while that of E. glawi occurs in the gall-bladder.     

Synthesis of shorter active analogues of Bactenecin7: The effect of change of N-terminal configuration on antimicrobial activity

Bactenecin7, a cationic antibacterial peptide, contains a repeating region of Xaa-Pro-Arg-Pro (Xaa = hydrophobic residues). A series of peptides, Xaa-Pro-Arg-Pro (Xaa = D-Ala, D-Leu, D-Val, D-Phe and D-Lys) were synthesized to investigate the effect of change of N-terminal configuration on antimicrobial activity. The conformationalpreferences of these peptides in water and TFE were examined by circular dichroism. All the synthetic peptides with D-amino acid substitution at N-terminal showed potent antifungal activity against Aspergillus niger, Aspergillus flavus and Fusarium moniliforme at the concentration level of 8–10 g ml^-1. But the same tetrapeptides were unable to kill or suppress the growth of gram-negativeand gram-positive bacteria such as Escherichia coli HB101, Pseudomonas aeruginosa, Klebsiella pneumoniae and Staphylococcus aureus even at the concentration level of 400 g ml^-1. The present study reveals that the change of configuration at the N-terminal of tetrapeptide has negative impact on antibacterial activity but enhanced antifungal activity.     

On the possible localization of a gene for triosephosphate isomerase on the short arm of human chromosome 5

Summary Chromosome 5 was examined by fluoresence microscopy in 13 individuals whose karyotype was 5p-. Great variation was observed in length (30–80% of the total short arm length), in type (translocation, interstitial and terminal deletions), and in localization of the deleted segment. There was no evidence of correlation between length, type or localization of deletion and triosephosphate isomerase activity. Triosephosphate isomerase activity of the 13 cases of karyotype 5p- was 2,74 moles/min/mg hemoglobin (95% confidence limits 2.49–3.32). Identical values were obtained in 16 normal individuals; 2.44 moles/min/mg hemoglobin (95% confidence limits 2.16–2.72). The present investigation does not confirm the postulated localization of the gene for triosephosphate isomerase on the short arm of human chromosome 5.

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Zusammenfassung 13 Patienten mit einem 5p—-Karyotyp wurden durch Fluorescenzuntersuchungen identifiziert und das Ausmaß der Deletion bestimmt. Triosephosphatisomeraseaktivitäten dieser 13 Fälle waren 2,74 mol/min/mg Hämoglobin, 95%-Vertrauensgrenzen 2,49–3,32.Identische Werte wurden bei 16 Normalpersonen gefunden (2,44 mol/min/mg Hämoglobin, 95%-Vertrauensgrenzen 2,16–2,72).Diese Befunde lassen sich dahingehend interpretieren, daß keine Assoziation zwischen Triosephosphatisomerase und Chromosom 5 besteht.

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Supported by the Research Committee of the Danish Mental Retardation Service (Project No. 106).     

Arabidopsis ammonium transporters,AtAMT1;1 and AtAMT1;2, have different biochemical properties and functional roles

We have compared the biochemical properties of two different Arabidopsis ammonium transporters, AtAMT1;1 and AtAMT1;2, expressed in yeast, with the biophysical properties of ammonium transport in planta. Expression of the AtAMT1;1 gene in Arabidopsis roots increased approximately four-fold in response to nitrogen deprivation. This coincided with a similar increase in high-affinity ammonium uptake by these plants. The biophysical characteristics of this high-affinity system (K_m for ammonium and methylammonium of 8 M and 31 M, respectively) matched those of AtAMT1;1 expressed in yeast (K_m for methylammonium of 32 M and K_i for ammonium of 1–10 M). The same transport system was present, although less active, in nitrate-fed roots. Ammonium-fed plants exhibited the lowest rates of ammonium uptake and appeared to deploy a different transporter (K_m for ammonium of 46 M). Expression of AtAMT1;2 in roots was insensitive to changes in nitrogen nutrition. In contrast to AtAMT1;1, AtAMT1;2 expressed in yeast exhibited biphasic kinetics for methylammonium uptake: in addition to a high-affinity phase with a K_m of 36 M, a low-affinity phase with a K_m for methylammonium of 3.0 mM was measured. Despite the presence of a putative chloroplast transit peptide in AtAMT1;2, the protein was not imported into chloroplasts in vitro. The electrophysiological data for roots, together with the biochemical properties of AtAMT1;1 and Northern blot analysis indicate a pre-eminent role for AtAMT1;1 in ammonium uptake across the plasma membrane of nitrate-fed and nitrogen-deprived root cells.     

The uptake of copper ions by cell suspension cultures of Agave amaniensis,and its effect on the growth,amino acids and hecogenin content

Cell suspension cultures of Agave amaniensiswere able to grow in media containing 10 – 240 M copper ions, and could remove more than 67% copper ions from the media. The cells accumulated up to 106 mg g^–1 copper ions in the biomass. Copper ions at 240 M caused a decrease in growth index and packed cell volume of the cultures of 61.5 and 53.3%, respectively. The presence of copper ions caused the cell walls to thicken and to be more wrinkled. Certain amino acids were released in high concentration into the media. The hecogenin content in the biomass increased up to 157.9% at 20 M copper ions.     

Grazing by a dominant rotifer Conochilus unicornis Rousselet in a mountain lake: in situ measurements with synthetic microspheres

Grazing rates of zooplankton were analysed in the summer of 1999 in Yellow Belly Lake, an oligotrophic system in the Sawtooth Mountains of Idaho (U.S.A.). The colonial rotifer Conochilus unicornis was a dominant species in the epilimnion, with densities reaching 20 colonies l^–1 (ca. 400 ind. l^–1). Clearance rates were measured with an in situ Haney Grazing chamber and synthetic microspheres 5, 9 and 23m in diameter. At epilimnetic temperatures of around 14 °C, mean clearance rates for 5m particles ranged from 30 to 65 l ind.^–1 h ^–1. Clearance rates were 2–9 times higher on the 5m spheres than on the 9 m spheres, and C. unicornis almost never fed on the 23 m spheres. Grazing rates did not change over the diel cycle. Clearance rates declined more than 10-fold as temperatures declined from 14 °C in the epilimnion to 7 °C in the metalimnion. In the epilimnion, grazing by C. unicornis was more important than grazing by crustaceans in the community, at least on particles 9m. The results show the importance of grazing by rotifers in lakes, and the significance of spatial variations that influence grazing rates.     

A lyophilized aqueous extract of<Emphasis Type="Italic"> Maytenus ilicifolia</Emphasis> leaves inhibits histamine-mediated acid secretion in isolated frog gastric mucosa

Lyophilized aqueous extract of Maytenus ilicifolia leaves (LAEMIL) is commonly used in Brazilian folk medicine in the treatment of dyspepsia as well as gastric ulcers. We have investigated the effect and the possible mechanism of action of the LAEMIL on acid secretion in isolated frog gastric mucosa incubated in an Ussing chamber. It was observed that LAEMIL (7–28 mg%) as well as cimetidine (125–4,000 M), a well-known histamine H₂ receptor antagonist, decreased basal acid secretion in a concentration-dependent manner. Similarly to cimetidine (190 M), LAEMIL (21 mg%) also inhibited gastric acid secretion induced by increasing concentrations of histamine (50–800 M). The EC₅₀ values for histamine alone and histamine in the presence of LAEMIL or cimetidine were 94.6 M (71.1–125.9 M), 244.9 M (209.4–286.4 M) and 142.2 M (23.6–855.0 M), respectively. LAEMIL, histamine and cimetidine were effective on acid secretion only when added to the serosal surface of the mucosa. Furthermore, simultaneous addition of LAEMIL and cimetidine at concentrations, per se, ineffective, caused a 16% reduction in the basal acid secretion [from 8.3±0.3 to 6.9±0.2 Eq g^–1 (15 min)^–1, n=4]. Although effects such as inhibition of histamine biosynthesis and/or histamine release can not be ruled out, our data suggest that LAEMIL, like cimetidine, reduces acid secretion in the isolated frog gastric mucosa by antagonising histamine H₂ receptors.Abbreviations LAEMIL Lyophilized aqueous extract of Maytenus ilicifolia leaves - Hist Histamine - Cim Cimetidine     

The Effect of Phenylalanine on DOPA Synthesis in PC12 Cells

DOPA synthesis from phenylalanine was studied in PC12 cells incubated with m-hydroxybenzylhydrazine, to inhibit aromatic L-amino acid decarboxylase. DOPA synthesis rose with increasing concentrations of either phenylalanine or tyrosine; maximal rates (~55 pmol/min/mg protein for tyrosine; ~40 pmol/min/mg protein for phenylalanine) occurred at a medium concentration of ~10 M for either amino acid. The K_m for either amino acid was about 1 M (medium concentration). At tyrosine concentrations above 30 M, DOPA synthesis declined; inhibition was observed at higher concentrations for phenylalanine (300 M). These effects were most notable in the presence of 56 mM potassium. Measurements of intracellular phenylalanine and tyrosine suggested the K_m for either amino acid is 20–30 M; maximal synthesis occurred at 120–140 M. In the presence of both phenylalanine and tyrosine, DOPA synthesis was inhibited by phenylalanine only at a high medium concentration (1000 M), regardless of medium tyrosine concentration. The inhibition of DOPA synthesis by high medium tyrosine concentrations was antagonized by high medium phenylalanine concentrations (100, 1000 M). Together, the findings indicate that for PC12 cells, phenylalanine can be a significant substrate for tyrosine hydroxylase, is a relatively weak inhibitor of the enzyme, and at high concentrations can antagonize substrate inhibition by tyrosine.     

Comparison of cyclopropene, 1-methylcyclopropene, and 3,3-dimethylcyclopropene as ethylene antagonists in plants

A comparison has been made of cyclopropene (CP), 1-methylcyclopropene (1-MCP), and 3,3-dimethyl-cyclopropene (3,3-DMCP) in their ability to protect plants against ethylene. In bananas, both CP and 1-MCP are effective around 0.5 nL L^–1, and 3,3-DMCP was effective at 1 L L^–1. Bananas treated with CP and 1-MCP again become sensitive to ethylene at 12 days and those treated with 3,3-DMCP at 7 days. Mature green tomatoes are protected by 5–7 nL L^–1 of 1-MPC for 8 days at 25°C and tomatoes treated with 3,3-DMCP at 5–10 L L^–1 are protected for 5 days. Carnation flowers are protected with CP or 1-MCP after exposure to 0.5 nL L^–1 for 24 hours and by 1 L L^–1 of 3,3-DMCP. The display life of Campanula flowers is increased from 3.3 to 5.4 days by 10 L L^–1 of 3,3-DMCP and to 9 days by 20 nL L^–1 of 1-MCP. Ethylene inhibition of pea seedlings is reduced by treatment with 1-MCP at 10 L L^–1 of ethylene but as ethylene is increased to 3000 L L^–1 growth inhibition increases. 3,3-DMCP treatment causes very little reduction of the ethylene effect even at very low concentrations.     

Asymmetric diffusion into the postsynaptic neuron: An extremely efficient mechanism for removing excess GABA from synaptic clefts on the Deiters' neurone plasma membrane

Microdissected Deiters' neuron plasma membranes have been used for studying the passage of GABA through the membrane both in the inward and outward direction. Working with 0.2 mM GABA in the compartment simulating the outside of the neurone and with 2.0 mM GABA in the one simulating the inside we found a net transport of GABA towards the inside. This mechanism does not require a Na⁺ ion gradient across the membrane. The nature of the transport process involved was studied by determining the rate of [³H]-GABA inward passage as a function of GABA concentration (1 nM–800 M) on the outward side of the membrane. The results have shown that until 50 M a diffusion process (v=D₁×C, where D₁=3.1×10^–11 1/m²×sec) is the sole mechanism involved. Above 50 M a second diffusion process is activated v=D₂×(C–50×10^–6), where D₂=2.8×10^–11 1/m²×sec. Taking in account both inward and outward directed diffusion, one can calculate 16 M as the equilibrium concentration of GABA on the outward side of the membrane. From a kinetic point of view, these diffusion processes are able to reduce GABA concentration in a synaptic cleft from 3 mM to 20 M within 3 sec. These diffusion systems are discussed as extremely efficient in removing the excess of released GABA in the synaptic cleft.     

Species-specific N and P release rates in Daphnia

Bioavailable N and P release rates by juveniles and adults of three Daphnia taxa (D. hyalina, D. galeata and its interspecific hybrids D. hyalina × galeata) were measured to assess the effect of weight and interspecific differences on these rates in Daphnia. Immobilized Scenedesmus obliquus cells were used to estimate the release rates. The specific release rate of N varied between 5.19–5.71 g N mg C^-1 h^-1 for juveniles and 3.00–3.42 g N mg C^-1 h^-1 for adults. P excretion rate ranged between 1.93–2.37 g P mg C^-1 h^-1 for juveniles and 1.00–1.24 g P mg C^-1 h^-1 for adults. Our results show that the taxonomic affiliation of Daphnia individuals did not affect their N and P release rates.     

Influence of inorganic microelements on the production of camptothecin with suspension cultures of <Emphasis Type="Italic">Camptotheca acuminata</Emphasis>

The effects of eight microelements (I^–, BO₃ ^3–, MoO₄ ^2–, Co²⁺, Cu²⁺, Mn²⁺, Fe²⁺, Zn²⁺) on the biosynthesis of camptothecin and the growth of suspension cultures of Camptotheca acuminata were studied. The increase of I^– to 25 M l^–1, Cu²⁺ to 1 M l^–1, Co²⁺ to 2 M l^–1 and MoO₄ ^2– to 10 M l^–1 in Murashige and Skoog (MS) medium resulted in 1.66, 2.84, 2.53 and 2.04 times higher of camptothecin yield than that in standard MS medium respectively. Combined treatment of I^– (25 M l^–1), Cu²⁺ (1 M l^–1), Co²⁺ (2 M l^–1) and MoO₄ ^2– (10 M l^–1) lead to improve cell dry weight, camptothecin content, and camptothecin yield to 30.56 g l^–1, 0.0299%, and 9.15 mg l^–1, respectively, which were 20.2, 208.9 and 273.8% increment respectively when compared with those of control.