Responses in stomatal conductance to elevated CO2 in 12 grassland species that differ in growth form

Responses in stomatal conductance (g _st ) and leaf xylem pressure potential ( _leaf ) to elevated CO₂ (2x ambient) were compared among 12 tallgrass prairie species that differed in growth form and growth rate. Open-top chambers (OTCs, 4.5 m diameter, 4.0 m in height) were used to expose plants to ambient and elevated CO₂ concentrations from April through November in undisturbed tallgrass prairie in NE Kansas (USA). In June and August, _leaf was usually higher in all species at elevated CO₂ and was lowest in adjacent field plots (without OTCs). During June, when water availability was high, elevated CO₂ resulted in decreased g _st in 10 of the 12 species measured. Greatest decreases in g _st (ca. 50%) occurred in growth forms with the highest potential growth rates (C₃ and C₄ grasses, and C₃ ruderals). In contrast, no significant decrease in g _st was measured in the two C₃ shrubs. During a dry period in September, reductions in g _st at elevated CO₂ were measured in only two species (a C₃ ruderal and a C₄ grass) whereas increased g _st at elevated CO₂ was measured in the shrubs and a C₃ forb. These increases in g _st were attributed to enhanced _leaf in the elevated CO₂ plants resulting from increased soil water availability and/or greater root biomass. During a wet period in September, only reductions in g _st were measured in response to elevated CO₂. Thus, there was significant interspecific variability in stomatal responses to CO₂ that may be related to growth form or growth rate and plant water relations. The effect of growth in the OTCs, relative to field plants, was usually positive for g _st and was greatest (>30%) when water availability was low, but only 6–12% when _leaf was high.The results of this study confirm the importance of considering interactions between indirect effects of high CO₂ of plant water relations and direct effects of elevated CO₂ on g _st , particularly in ecosystems such as grasslands where water availability often limits productivity. A product of this interaction is that the potential exists for either positive or negative responses in g _st to be measured at elevated levels of CO₂.     

Effects of large Saduria entomon (Isopoda) on spatial distribution of their small S. entomon and Monoporeia affinis (Amphipoda) prey

We performed laboratory experiments to investigate the effects of predator avoidance and numerical effects of predation on spatial distribution of small Saduria entomon (Isopoda) and Monoporeia affinis (Amphipoda), with large S. entomon as predators. The horizontal distribution and mortality of the prey species, separately and together, were studied in aquaria with a spatial horizontal refuge. We also estimated effects of refuge on mortality of small S. entomon and M. affinis by experiments without the refuge net. In addition, we investigated whether predation risk from large S. entomon influenced the swimming activity of M. affinis, to clarify the mechanisms behind the spatial distribution. Both small S. entomon and M. affinis avoided large S. entomon. The avoidance behaviour of M. fffinis contributed about 10 times more to the high proportion in the refuge than numerical effects of predation. Due to the low mortality of small S. entomon the avoidance behaviour of this species was even more important for the spatial distribution. The combined effect of avoidance behaviour and predation in both species was aggregation, producting a positive correlation between the species in density. M. affinis showed two types of avoidance behaviour. In the activity experiments they reduced activity by 36% and buried themselves in the sediment. In the refuge experiments we also observed avoidance behaviour with the emigration rate from the predator compartment being twice the immigration rate. The refuge did not lower predation mortality in M. affinis, probably due to the small scale of the experimental units in relation to the mobility of the species. Predation mortality in small S. entomon was higher in absence of a refuge and especially high in absence of M. affinis.     

Novel cyanoguanidines with potent oral antitumour activity

4-Pyridyl cyanoguanidines with hydrophobic aromatic side chains showed potent antiproliferative activity in the human breast and lung cancer cell lines MCF-7, NYH and H460. In vivo, treatment with N-(6-chlorophenoxyhexyl)-N′-cyano-N″-4-pyridylguanidine (18, 20 mg/kg/day po.), gave a complete remission of tumours in a model of NYH inoculated nude mice.     

Light-induced swimming of Daphnia: can laboratory experiments predict diel vertical migration?

Vertical displacement velocity of a Daphniagaleata × hyalina clone was quantified inrelation to changes in the relative rate of lightchange. An increase in the latter variable triggers anenhanced swimming response, and this response is againelicited when a second increase in the rate ofrelative light increase is applied. Decreases in therate of light increase affect phototactic swimming ina similar way. The acceleration/deceleration assistedstimulus-response system is an extension of the ideaof phototaxis as the underlying behavioural mechanismfor vertical migration, and suggests that continuousaccelerations in light change also affect verticaldisplacements observed in the field. A simple dielvertical migration simulation model was used tocalculate the vertical displacement of Daphniain relation to the natural light change at sunrise.The calculated vertical displacement fits nicely inthe temporal range of the observed averaged downwardmigration of adult Daphnia in Lake Maarsseveen.The calculated migration amplitude, however, islarger than the change in mean population depthobserved in nature.     

Surface water chemistry characteristics in the Lake Storgrønningen drainage area, Høylandet, during periods of high and low discharge

The surface water chemistry of Høylandet has beenstudied by performing two synoptic surveys, duringhigh runoff in the autumn of 1986 and during a lowflow period in the summer of 1988. Based on watersamples of up to 38 chemical variables from 75 sites,analyses show considerable variation in the chemicalcomposition. There is a strong altitude gradient, i.e.very dilute poorly buffered waters dominate at higherelevations near the timberline while progressivelyhigher salt content and alkalinities arecharacteristic at lower altitudes more dominated byforests. The influence of mires is less pronounced.The overall water quality is of oligotrophic naturewith low concentrations of strong acid anions andmetals known to be enriched under acidifiedconditions. The natural pH gradients are considerablebut with no indication of anthropogenic acidification.The data provide little support for the hypothesisthat in-catchment production of organically derivedacidity leads to acid runoff, which in thesecatchments appears compensated by increasedweathering. The findings are in general accordancewith other Høylandet catchment studies. It isconcluded that this area may serve as a representativepristine surface runoff analogue for catchmentscurrently affected by atmospheric deposition of strongmineral acids.     

Modeling the leech heartbeat elemental oscillator I. Interactions of intrinsic and synaptic currents

We have developed a biophysical model of a pair of reciprocally inhibitory interneurons comprising an elemental heartbeat oscillator of the leech. We incorporate various intrinsic and synaptic ionic currents based on voltage-clamp data. Synaptic transmission between the interneurons consists of both a graded and a spike-mediated component. By using maximal conductances as parameters, we have constructed a canonical model whose activity appears close to the real neurons. Oscillations in the model arise from interactions between synaptic and intrinsic currents. The inhibitory synaptic currents hyperpolarize the cell, resulting in activation of a hyperpolarization-activated inward currentI _h and the removal of inactivation from regenerative inward currents. These inward currents depolarize the cell to produce spiking and inhibit the opposite cell. Spike-mediated IPSPs in the inhibited neuron cause inactivation of low-threshold Ca⁺⁺ currents that are responsible for generating the graded synaptic inhibition in the opposite cell. Thus, although the model cells can potentially generate large graded IPSPs, synaptic inhibition during canonical oscillations is dominated by the spike-mediated component.     

Occurrence of α-acetolactate decarboxylases among lactic acid bacteria and their utilization for maturation of beer

Summary Acetolactate decarboxylase activity has been detected among three genera, nine species and 263 strains of lactic acid bacteria tested in the course of a screening for acetolactate decarboxylases amenable for use in brewing as maturation aid. Streptococcus diacetylactis strain FD-64-D was found to generate a decarboxylase exhibiting a satisfactory activity and an excellent stability at the pH prevailing in beer and wort. This decarboxylase could not be solubilized but enzymatically active, freeze-dried cells were effective for satisfactory flavour maturation of beer although difficulties were encountered during attempts to remove the applied cell material by filtration of the beer. Lactobacillus casei DSM 2547 was likewise found to produce a decarboxylase exhibiting a satisfactory activity and stability at the low pH of beer and which, in addition, was readily solubilized. A method has been developed for pilot scale production of preparations of this decarboxylase suitable for use in brewing.Abbreviations DSM Deutsche Sammlung von Microorganismen - EDTA Ethylene diaminetetra-acetic acid     

Freeze-preservation of rice cells: A physiological study of freeze-thawed cells

Rice ( Oryza sativa L.) cells returning to in vitro culture after preservation at superlow temperature in liquid nitrogen are characterized by a number of physiological alterations. These include: reduction in respiration and glucose uptake, loss of intracellular potassium, decrease in the cellular level of key metabolites (ATP, glucose-6-phosphate and pyruvate) and fragility of protoplasts following the action of cell wall-degrading enzymes.
Nevertheless, cell growth resumes after a short lag phase (2–4 days) with an actual 70–100% cell survival, thus indicating that the observed damage is not lethal and can be repaired in a short time.     

Classification of basiphilous pine forests in Telemark, SE Norway: a numerical approach

The basiphilous pine forests in southern Telemark, SE Norway, have previously been classified according to the ordinary phytosociological methods of the Braun—Blanquet system. The same material was later treated by numerical analysis, i.e., TABORD—classification and the ordination technique 'reciprocal averaging'. No significant differences were found between the numerical and the non—numerical classification except for the classification of some transitional communities. Ordination by 'reciprocal averaging' gave a useful complement to the TABORD classification, and re—leves and species were distributed along interpretable gradients (i.e., along a dry—wet gradient and along a gradient from forest—rim conditions to forest conditions).     

Inhibition of an abdominal proprioceptive reflex in crayfish

Summary Stimulation of the tonic muscle receptor organs inProcambarus clarkii results in reflex activation of the superficial extensors. This pathway is inhibited by activity in the lateral giant fibers and both medial giants. A labile synapse in the same pathway works synergistically with the giant fiber-mediated inhibition to prevent maladaptive activation of the superficial extensors during escape behavior. Evidence did not support the notion of giant fiber-mediated peripheral inhibition (via the accessory nerve) of MRO activity.This work was supported by NIH grant NS 02944 (to D. Kennedy). I would like to thank Drs. Kennedy, Wine, and the members of the Kennedy laboratory for their help and support.