Short period leaf movements in Oxalis regnellii

Oxalis regnellii Mig. is a trifoliate plant, and the three leaflets usually show synchronized up and down movements with a circadian period of 26–27 h. The three leaflets can also perform desynchronized ultradian oscillations, and we report on such rhythms under different conditions. A study of the occurrence of ultradian leaf movement rhythms as a function of irradiance is presented. At an irradiance of approximately 1 μW cm⁻², the occurrence was maximal and ca 30%. The periods varied from 5 to 15 h. Four other cases of ultradian rhythms in different conditions are also presented. In one case spontaneous ultradian rhythms occurred, and in another, two of the leaflets showed ultradian rhythms when the third leaflet had received a light pulse. In two more cases, the three leaflets on a leaf were separated by physical cuts along the petiole between the pulvini; in both cases the period was approximately 5 h. Possible mechanisms to explain the ultradian rhythms in Oxalis regnelli are discussed.     

Do Arctic waders use adaptive wind drift?

We analysed five data sets of flight directions of migrating arctic waders in relation to winds, recorded by tracking radar and optical range finder, in order to find out if these birds compensate for wind drift, or allow themselves to be drifted by winds. Our purpose was to investigate whether arctic waders use adaptive wind drift strategies or not. The data sets were collected in Siberia (two sets) and Canada during post-breeding (autumn) migration, and in Mauritania and South Sweden during pre-breeding (spring) migration. Both significant drift and compensation effects were found in three of the data sets, Canada, Mauritania and South Sweden. Almost no compensation was found in birds departing in easterly directions from the Siberian tundra (complete drift), while no drift effect was found in birds departing in westerly directions (complete compensation). There were indications that at least some populations of waders may use an adaptive drift strategy consisting of drift at high altitude and/or in high wind speed combined with compensation at low altitude and/or in lower wind speeds, but support for this idea was rather weak and not consistent. Our results were instead more in accordance with the adaptive drift theory that predicts initial drift during the migratory journey, followed by compensation during later stages as the birds are approaching their destinations. Such a strategy implies that arctic waders, at least adult birds, have the capacity of true navigation. A comparison with earlier studies of migrating arctic waders from different parts of the world show that all results so far may be interpreted in accordance with this general adaptive drift strategy. An element of non-adaptive drift can, however, not be completely ruled out.     

PATTERNS AND LABELLING CHARACTERISTICS IN NEURONAL AND GLIAL RNA

Abstract— Rabbit cortex slices were incubated in a medium containing [³H]-uridine for various periods of time. Following incubation, neuronal and glial cell fractions were prepared on a discontinuous Ficoll-sucrose gradient. RNA was extracted from neurons and glia with a tris-sodium dodecyl sulphate-phenol solution and fractionated on a composite agarose-polyacrylamide gel. The stained gel showed major bands corresponding to 28 s , 18 s , 5 s and 4 s fractions and additional minor bands at the position of 24 s , 21 s and 13 s. Neuronal and glial RNA had the same general RNA pattern but the 5 s fraction was more pronounced in neuronal RNA and 4 s more pronounced in glial RNA. After 30 min labelling both neuronal and glial RNA had maximum activities in fractions higher than 28 s with a peak corresponding to 45 s . In the lower mol. wt. region the labelling was essentially poly-disperse. With increasing incubation time, peaks corresponding to 38 s and 32 s appeared as well as to ribosomal and soluble fractions. Incorporation of activity into total RNA expressed as d.p.m/ μ g of nucleic acids, showed similar labelling in neurons and glia after 30 and 60 min and a 3-4 times higher incorporation into neuronal RNA after 180 min. The possible implications of these results are discussed.     

Effect of Serine and Ethanolamine Administration on Phospholipid-Related Compounds and Neurotransmitter Amino Acids in the Rabbit Hippocampus

Abstract: The report concerns mechanisms for the increase of extracellular levels of ethanolamine and phosphoethanolamine in CNS regions, such as the hippocampus, in transient brain ischemia, hypoglycemia, seizures, etc. l -Serine (2.5–10 m M ), d -serine (10 m M ), or ethanolamine (10 m M ) was administered for 20 min via a microdialysis tubing to the hippocampus of unanesthetized rabbits. The concentrations of primary amines were determined in the dialysates. When levels were elevated 10–100 times in the extracellular fluid, l -serine caused a dose-dependent increase of the concentration of extracellular ethanolamine. Ethanolamine caused a corresponding, although somewhat smaller, increase in serine levels. Furthermore, l -serine also induced an increased concentration of phosphoethanolamine that was delayed in time relative to the peak of ethanolamine. d -Serine was as effective as l -serine in raising ethanolamine levels but had no effect on phosphoethanolamine. Ethanolamine, but not l -serine, also increased extracellular glutamate/aspartate levels in an MK-801-dependent fashion. A similar effect, but delayed in time, was observed with d -serine. These effects were inhibited by MK-801. The concentrations of other amino acids were not significantly affected. The characteristics of the effects are suggestive of base exchange reactions between serine and ethanolamine and between ethanolamine and serine glycerophospholipids, respectively, in neuronal plasma membranes.     

The effects of electrical stimulation of posterior hypothalamus on activity of the nucleus pontis oralis' neurons

The nucleus pontis oralis' neurons were responsive to electrical stimulation of posterior hypothalamus. PS-on neurons showed an inhibitory response, and PS-off cells demonstrated an excitatory response. Neurons that discharged in association with phasic paradoxical sleep phenomena were found to have both the excitatory and the inhibitory responses. Evoked responses changed across sleep-waking cycle. The findings suggest that posterior hypothalamus is involved in the control of paradoxical sleep generation mechanisms located in the nucleus pontis oralis.     

Furan in heat-treated foods: Formation, exposure, toxicity, and aspects of risk assessment

Furan is formed in a variety of heat-treated foods through thermal degradation of natural food constituents. Relatively high levels of furan contamination are found in ground roasted coffee, instant coffee, and processed baby foods. European exposure estimates suggest that mean dietary exposure to furan may be as high as 1.23 and 1.01 μg/kg bw/day for adults and 3- to 12-month-old infants, respectively. Furan is a potent hepatotoxin and hepatocarcinogen in rodents, causing hepatocellular adenomas and carcinomas in rats and mice, and high incidences of cholangiocarcinomas in rats at doses ≥2 mg/kg bw. There is therefore a relatively low margin of exposure between estimated human exposure and doses that cause a high tumor incidence in rodents. Since a genotoxic mode of action cannot be excluded for furan-induced tumor formation, the present exposures may indicate a risk to human health and need for mitigation. This review summarizes the current knowledge on mechanisms of furan formation in food, human dietary exposure to furan, and furan toxicity, and highlights the need to establish the risk resulting from the genotoxic and carcinogenic properties of furan at doses lower than 2 mg/kg bw.     

Influence of the g-force on the circumnutations of sunflower hypocotyls

Circumnutations of hypocotyls of sunflower ( Helianthus annuus L. cv. Californicus) were studied under 1 g and 3 g conditions. Root mean square values of the hypocotyl deviation from the plumbline and period of the movements were determined from Calculations of the autocorrelation functions of the movements. The amplitude and the period of the circumnutations increased under 3 g as compared to 1 g . A transition from 3 to 1 g or vice versa also caused changes in period and amplitude of the movoments. The results are interpreted as a support for the idea that gravity influences the circumnutation parameters in this sunflower variety. A comparison is made with published results on the dwarf sunflower ev. Teddy Bear where the force influence is very small or negligible. Simulations of a model for circumnutations show movements which are in qualitative agreement with the experimental results, provided adaptation to g -levels is included in the model. Finally, the results are discussed with the recent Spacelab-experiment (SLI) as a background.     

Gravitropically-stimulated seedlings show autotropism in weightlessness

In a spaceflight experiment, autotropism by oat ( Avena sativa L.) coleoptiles following gravitropic responses was prominent in weightlessness: counter-reactions led to the straightening of the curved coleoptiles. This was not the case during clinorotation on earth. The autotropic reactions appeared to be related to the stimulus received during the stimulus period, i.e. the greater the response the greater the autotropic counter-reaction. Previous models of the gravitropic system which predicted that coleoptiles would not straighten in weightlessness are disproved. A modification to one of the models is proposed which includes the autotropic response observed in spaceflight. The nature of the counter-reactions in the absence of gravitropic stimulation is discussed.