Stable carbon isotopes in tree rings of beech: climatic versus site-related influences

 Stable carbon isotopes in tree rings are a promising tool in palaeoclimate research, provided attempts are made to disentangle climatic from local effects (e.g. soil properties, competition, light). The ¹³C/¹²C variations in cellulose of tree rings of beech (Fagus sylvatica) were determined at several sites in the Swiss Central Plateau covering the last 50 years. We chose sites which differ in moisture conditions and sampled cores from four to six trees per site. The mean ¹³C/¹²C series from the different dry sites (distant by up to 40 km) are closely interrelated suggesting a common external cause. Correlation analysis with climate data proved the total precipitation in the months May, June and July to have the strongest effect on the carbon isotopes (r =  – 0.73). This result is in agreement with the commonly used model which relates the isotope discrimination to the water use efficiency. On the other hand, the isotope series of the wet sites are not as well correlated to the climate. At two of the sites (a dry and a humid) tree ring width suddenly increased. We used this effect as a test-case to study the influence of local growth conditions on the climate-isotope relationship. Received: 17 April 1996 / Accepted: 2 September 1996     

SOURCES OF INORGANIC CARBON FOR PHOTOSYNTHESIS BY THREE SPECIES OF MARINE DIATOM1

The utilization of inorganic carbon by three species of marine diatom, Skeletonema costatum (Grev.) Cleve. Ditylum brightwellii (West) Grun., and Chaetoceros calcitrans Paulsen was investigated using an inorganic carbon isotopic disequilibnum technique and inorganic carbon dose-response curves. Stable carbon isotope data of the diatoms are also presented. Observed rates of photosynthetic oxygen evolution were greater than could be accounted for by the theoretical rate of CO₂ supply from the uncatalyzed dehydration of HCO₃^? in the external medium, suggesting use of HCO₃^? as an inorganic carbon source. Data from the isotopic disequilibrium experiment demonstrate the use of both HCO₃^? and CO₂ for photosynthesis. Carbon isotope discrimination values support the use of HCO₃^? by the diatoms.     

Stable-isotope studies on the collagenic and hydroxylapatite components of fossils: Palaeoecological implications

Collagenic material has been extracted and analysed for stable carbon- and nitrogen-isotope ratios from Henschke Cave, a Late Pleistocene fossil locality, South Australia. The carnivore Thylacoleo carnifex most likely consumed omnivores ( Parameles spp.) with a palaeodiet of C₃ plant material under a forest canopy, which was also recorded in the herbivores analysed ( Macropus spp., Sthenurus spp. and Diprotodon spp.). A forested environment supports previous interpretations of extant fauna and their modern habitats. The presence of negative nitrogen-isotope ratios in herbivores has been interpreted as non-diagenetic on the basis of carbon/nitrogen ratios and amino acid spectra, and in fact may be indicative of acidic soils. Analyses on bone and enamel carbonate hydroxylapatite from the same species support the conclusion that bone is unreliable for palaeoecological and palaeoclimatological research. However, bone carbonate hydroxylapatite may prove valuable in assessing the extent of isotopic fractionation during diagenesis. A review of carbon-isotope analyses on fossil collagenic material and enamel carbonate hydroxylapatite suggests a carnivore-herbivore boundary. The application of this boundary in palaeoecological research requires further investigation. Future palaeoecological research on fossils needs to incorporate stable-isotope analyses on the carbonate hydroxylapatite and collagenic components of fossils.     

Establishment and maintenance of the breeding territory in the polygynous great reed warbler

Settlement of male great reed warblers in the breeding ground was highly asynchronous at Lake Biwa in Japan. It took over 1 month from the appearance of the first male to a saturation in number of males. In resource-defense-polygyny, males are expected to try to defend as large an area as possible in the optimal habitat. In fact, a small number of the earliest settling males divided up the breeding ground almost completely as territories among themselves and these were later reduced in size with the addition of later settlers. The reduction was not due to a seasonal decline of aggressiveness on the part of the owners but to a higher level of intrusion pressure by later arriving males. The neighbor-neighbor relationship, once established, was rather stable. Home range overlap was small and territorial contacts were few between neighbors. Territorial boundaries seem not to shift despite the addition of new males as long as the neighbors were the same. The stable relationships between neighbors are expected to help the earlier resident to maintain his large and good territories throughout the breeding season and hence polygyny is favored in this species.     

Efficient membrane targeting of the chick nicotinic acetylcholine receptor α-subunit in stable insect cell lines

We have synthesised the -subunit of the chick nicotinic acetylcholine receptor (nAChR) in stable, continuous insect (Spodoptera frugiperda) cell lines. A cDNA was integrated randomly into the insect cell genome under control of a baculovius immediate early gene promoter. Transformed cells were obtained by co-transfection of the insect cells with pIEK1.nAChR, encoding the -subunit cDNA, and pIEK1.neo, encoding the neomycin resistance gene. G-418-resistant clones were selected and expanded into continuous cell lines synthesising the chick nAChR -subunit. Using fluorescence microscopy and ligand binding studies we were able to demonstrate efficient membrane targeting of the receptor subunit in the insect cell plasma membrane. Stable insect cell lines may thus have significant advantages over transient baculovirus vectors for the synthesis and characterisation of heterologous receptor proteins.Abbreviations AcNPV Autographa californica nuclear polyhedrosis virus - BTX -bungarotoxin - BSA bovine serum albumin - FITC Fluoroscein isothiocyanate - G418 geneticin-418 - hpi hours post-infection - ie-1 immediate early 1 gene - nAChR nicotinic acetylcholine receptor alpha subunit - Sf Spodoptera frugiperda - tPA tissue plasminogen activator     

Stabile production of a thrombin resistant pro-urokinase derivative (PRO-UKS1) by Namalwa KJM-1 cells adapted to serum-free medium

Pro-UKS1 was designed as a thrombin-resistant derivative of pro-urokinase (pro-UK) by introducing a glycosylation site using site-directed mutagenesis. An expression plasmid for pro-UKS1, pMo1UKS1SEd1-5, was constructed and introduced into Namalwa KJM-1 cells (Hosoiet al., 1988), and cells resistant to G418 and Methotrexate (MTX) were obtained. Amongst them, the highest pro-UKS1 producer (resistant to 500 nM of MTX), clone 41-8, was selected and further characterized. Clone 41-8 was cultured in serum-free ITPSGF medium (Hosoiet al., 1988). Under the conventional conditions, the concentration of pro-UKS1 reached 26 g ml^–1. Addition of glucose and tri-iodothyronine (T₃) improved productivity, and the maximal productivity of pro-UKS1 was 67 g ml^–1 day^–1. In this conditioned medium, content of pro-UKS1 was above 80% of total proteins.Abbreviations BSA bovine serum albumin - dhfr dihydrofolate reductase - HEPES 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - kb kilobase pairs - kDa kilodaltons - MTX Methotrexate - PBS phosphate buffered saline - pro-UK pro-urokinase - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis - T₃ tri-iodothyronine - Tween-PBS phosphate buffered saline containing 0.05% Tween 80     

Chloroherpeton thalassium gen. nov. et spec. nov., a non-filamentous,flexing and gliding green sulfur bacterium

A flexing and gliding green sulfur bacterium has been isolated from marine sources off the North East coast of the USA. Chloroherpeton thalassium is an obligate phototroph, and requires CO₂ and S^2- for growth; some organic acids can contribute to cell carbon, and N₂ may be fixed. The cells contain typical chlorosomes, and gas vesicles may be present. Bacteriochlorophyll c is the main light harvesting pigment, and a small quantity of bacteriochlorophyll a is also present. Over 80% of the carotenoid is -carotene. DNA base composition of the isolates ranges from 45.0–48.2 mol% G+C.In memory of R. Y. Stanier     

Development of regulation mechanisms for SO42- influx in spring wheat roots

The development of SO₄^2- influx in roots and sulfur transport to shoots was followed in ³⁵S-tracer experiments for sulfur-deficient spring wheat (Triticum aestivum L. cv. Svenno) seedlings pretreated for various time periods (0–24 h) in nutrient solutions with SO₄^2-. Effects of the metabolic inhibitor 2,4-dinitrophenol (DNP) and the protein synthesis inhibitor cycloheximide (CH) on SO₄^2- influx were also evaluated. The SO₄^2- influx appears feedback-regulated by the internal sulfur level of the roots. Regulation may be achieved solely by a rapidly changed SO₄^2- carrier activity through an allosteric effect by the intracellular SO₄^2- concentration of the roots, followed first by induction of carrier synthesis and then by repression of carrier synthesis after transfer of the roots from SO₄^2--deficient nutrient solutions to solutions with SO₄^2-. A Hill plot of the partly sigmoidal relationship between SO₄^2- influx and intracellular sulfur concentration in the roots gave a Hill coefficient of -4.2, indicating negative cooperativity between a minimum number of four interacting allosteric binding sites for sulfur on each carrier entity. DNP-experiments showed that SO₄^2- influx was mainly metabolic, especially after short pretreatment in SO₄^2- at an external SO₄^2- concentration of 0.1 mM. Pretreatment with CH rapidly prevented new SO₄^2- carriers from being formed. Long CH pretreatment (24 h) and different SO₄^2- pretreatments reduced SO₄^2- influx below the non-metabolic level obtained by uptake experiments with DNP, indicating the existence of SO₄^2- carriers mediating passive SO₄^2- transport across the plasmalemma of the root cells. SO₄^2- influx was further decreased for the CH pretreated (24 h) plants by the presence of both CH and DNP in the experimental nutrient solution. This probably indicates the diffusive part of the non-metabolic SO₄^2- influx in the present experiments. Finally, it is suggested that there is a feedback signal between root and shoot, regulating sulfur transport upwards.     

Phloem transport of sulfur in Ricinus

Mature leaves of Ricinus communis fed with ³⁵SO ₄ ^2- in the light export labeled sulfate and reduced sulfur compounds by phloem transport. Only 1–2% of the absorbed radiosulfur is exported to the stem within 2–3 h, roughly 12% of ³⁵S recovered was in reduced form. The composition of phloem translocate moving down the stem toward the root was determined from phloem exudate: 20–40% of the ³⁵S moved in the form of organic sulfur compounds, however, the bulk of sulfur was transported as inorganic sulfate. The most important organic sulfur compound translocated was glutathione, carrying about 70% of the label present in the organic fraction. In addition, methionine and cysteine were involved in phloem sulfur transport and accounted for roughly 10%. Primarily, the reduced forms of both, glutathione and cysteine are prsent in the siever tubes.Abbreviations CySH cysteine - GSH glutathione - GSSG glutathione disulfide - NEM N-ethylmaleimide - CyS-SCy cystine