Showing papers in "Naturwissenschaften in 1996"

Does bee color vision predate the evolution of flower color

Abstract: Many species of bees depend obligatorily on pollen and nectar offered by flowers of angiosperm plants. It is thus reasonable to assume that the components of the sensory system of such insects were adapted to maximize the distinctiveness and detectability of floral food sources. Indeed, the bees' UV, blue, and green receptors are optimally placed on the wavelength scale for discrimination of flower colors [1]. However, to prove that flower signals indeed influenced wavelength tuning of bee spectral receptors, it must be shown that the ancestors of bees possessed different sets of such receptors prior to the advent of the angiosperms. How can we determine the spectral receptor types through which insects saw the world 200 million years (Ma) ago? One has to evaluate members of arthropod taxa whose evolutionary lineages diverged from those of bees before there were flowers. If the spectral receptor sets of such animals are indistinguishable from those of bees, this implies that essential components of insect color vision predated the evolution of flower color. To test this possibility, the )~max values of a large number of species were superimposed on the phylogenetic tree of the arthropods (Chelicerata, Crustaceae, and Antennata, including the Insecta). Only species whose phylogenetic position could be unambiguously determined according to the literature [2 -6] were included. Diptera and Lepidoptera will be treated ] n a separate-study (Chittka, in prep.). The following trends are apparent in Fig. 1. The 2m~ values of the Crustacea and Insecta fall into three distinct clusters around 350, 440, and 520 nm. The Chelicerata, including jumping spiders [7, 8] and horseshoe crabs [9] lack blue receptors consistently; ERG measurement from scorpions confirm this picture [10]. In contrast, almost all Mandibulata possess at least the above three color receptor types. Thus, the blue receptor appears to be an evolutionary novelty in the ancestor of the Mandibulata. The few insect species in which one of these types is absent (Periplaneta [11] and Myrmecia [12]) clearly represent cases in which these receptors were lost secondarily. Red receptors show up irregularly in both the Crustacea and Insecta; they have obviously evolved several times independently. To see whether the wavelength positions of UV, blue, and green receptors depend on whether their bearers are flower visitors or not, we compared the )~,~ values of these receptor classes between the Hymenoptera [H] and the remaining arthropods with three spectral photoreceptor classes [A] in Fig. 1 by means of the Mann-Whitney U test. No statistically significant difference is found for the UV receptors (mean J'max [H] = 343 nm; m e a n ~'max [A] = 349 nm; p = 0.44) and the blue receptors (mean)~max [H] = 434 nm; mean 2ma x [A] = 433 nm; p = 0.36); however, the distributions of green receptors differ significantly between these two groups of arthropods (mean)~max[H] = 535 nm; m e a n 2ma x [A] = 521nm; p = 0.012). Unfortunately, the color receptors of only few species of Crustacea were studied by means of intracellular measurements. There is actually more diversity in wavelength positions of crustacean photoreceptors than Fig. 1 (which focuses on data from intracellular recordings) might suggest. Since the evaluation of spectral receptor types in Crustacea is crucial to understanding the evolution of receptor wavelength tuning in their sister group, the Antennata (including the insects), a separate graph is shown which also includes species whose 2ma x have been determined by microspectrophotometry and ERG measurements.

Embryonic Angiogenesis: A Review

Abstract: Supply with nutrients is essential from early embryonic stages onwards. Therefore, circulatory organs form the first functioning organ system. With the exception of the heart, this system is at first formed by only one cell type, the endothelial cell. Emergence, behavior, and differentiation of endothelial cells are discussed in this review. At first, endothelial cells develop from angioblasts (primary angiogenesis/angioblastic development), later they develop from preexisting endothelial cells (secondary angiogenesis/angiotrophic growth). The composition of the extracellular matrix may promote or inhibit angiogenesis. Various growth factors which can be bound to the extracellular matrix may have been found, but only two of them (VEGF, P1GF) seem to influence endothelial cell behavior directly. Heterogeneity and organ-typical differentiation of endothelial cells seem to be dependent on cell-cell signaling within each organ.

ENSO-controlled flooding in the Paraná River (1904–1991)

Abstract: Since the poineering work of Walker [1, 2], evidence has been mounting that the E1Nifio-Southern Oscillation (ENSO) phenomenon causes rainfall anomalies in various parts of the globe [3, 4]. These anomalies are particularly well defined over the region of South America [4 6]. Rivers exhibit the advantage of being rainfall integrators over large areas. This approach was used by Richey et al. [7], who have shown a significant (5% level) coherent relationship in the crossspectral analysis of deseasonalized Amazon discharge data and atmospheric pressure anomalies at Port Darwin, Australia. Precipitation over the Amazon basin appears to be stimulated by the ascending motions associated with the Southern Oscillation (SO) positive phase and, hence, its positive level departures occur mainly during cold events, also known as La Nifia [31. Early in the study of the SO, a keen interest arose on the connection which might exist between the SO and the flow regime of the Paranfi River. Originally Mossman [8], and, a few years later, Bliss [9], pointed to the relationship of the SO with rainfall over southern Brazil, Paraguay, and northern Argentina, as presented by the level of the Paranfi River 420 km above the mouth, at Rosario, Argentina. In opposition to the Amazon, the Paranfi positive level departures are significantly correlated with ENSO warm extremes. Moreover, the "season" of ENSO-related precipitation in the Paranfi River drainage basin is in phase with the normal annual precipitation cycle [10], thus causing flooding events often disastrous during E1 Nifio years. To the best of our knowledge, the Paranfi is the largest river system in the world which exhibits such a behavior. A relatively long record of the Paranfi discharge oscillations is available for the Corrientes section (Fig. l). In analyzing this daily record (Fig. 2A), we seek to establish the frequency of the variability and the significance of the teleconnection with the ENSO phenomenon. This record reflects the hydrologic conditions prevailing over 1.95 x 106 km 2 (ca. 70o7o of the total basin area), including the runoff supplied by the Andean headwaters of the Bermejo and Pilcomayo rivers, the discharge provided by the Mato Grosso through the Paraguay River, and the water output delivered by the Upper Paranfi River basin with headwaters in Brazil's Serra dos Preneos. When the discharge time series of Fig. 2A is considered, the most outstanding features which arise are the pronounced seasonality with high waters in February/March and low waters in August/September the substantial variability, and the magnitude of the 1982/83 flood. This flood, obviously related to the strong 1982 E1 Nifio event, caused profound modifications in the biogeochemical functioning of the river [l l , 12]. Other large floods, such as those of 1904, 1911, 1932, and 1965, also occurred in accordance with ENSO warm events [4]. Worthy of attention are the negative deviations in the record (Fig. 2B), which persisted longer than positive ones, at least until

Trapping of viruses in high-frequency electric field cages

Abstract: High-frequency electric field cages can stably trap cells and microparticles in aqueous media [1, 2]. Such cages can be made by semiconductor fabricat ion techniques and are not to be confused with electromagnetic field devices used for t rapping atomic and elementary particles [3]. The behavior of various dielectric microparticles in uniform and nonuniform a.c. electric fields was investigated by Pohl in the 1970s and discussed in his monograph [4]. The mot ion of individual cells in nonuniform a.c. fields, termed dielectrophoresis (DP), was studied in subsequent decades [5]. The force, F, acting on a spherical dielectric particle of radius, r, in a timeperiodic electric field, f , can be expressed as a dipole approximat ion by

Stress and the immune system

Abstract: Research in psychoneuroimmunology has demonstrated that biopsychosocial factors such as psychological stress can influence the immune system. Chronic stress has been associated with the suppression of the immune function. In contrast, acute psychological stressors and physical exercise have been shown to transiently enhance immune responses. These stress effects on immunity seem to be mediated via endocrine factors, since hormones, neurotransmitters, and neuropeptides can interact with cellular components of the immune system. In summary, experimental and clinical evidence suggests a functional relationship between stress, immunity, and diseases.

Perception of Carbon Dioxide and Other "Air-Condition" Parameters in the Leaf Cutting ant Atta cephalotes

Abstract: Social insects often build subterranean nests to protect themselves and their brood from predators and environmental influences. These nests can reach remarkable sizes, covering an area of up to 40 m and reaching 6 m below the surface [1]. The fungus gardening leaf cutting ants (genus Atta) have special demands for their nests, including stable microclimatic conditions required by the fungus. The climatic parameters, such as humidity, temperature, and the concentration of CO2 , have direct impact on the development of the brood and on the fitness of the whole colony [2]. The ants appear to be able to regulate these conditions by constructing and, when needed, altering ventilation channels, which are an important part of the nest [3]. Various types of sensilla, often hairshaped sensory organs with up to 30 receptor neurons densely cover the antennae and perceive chemical and mechanical stimuli. In A. cephalotes there are about 1400 sensilla on each antenna, and thus an enormous number of sensory cells relay the information to the brain [4]. In addition to pheromones, food odors, and mechanical stimuli, changes in environmental parameters are detected by antennal sensilla.

The diaphorase subunit HoxU of the bidirectional hydrogenase as electron transferring protein in cyanobacterial respiration

Abstract: The bidirectional hydrogenase in cyanobacteria is a tetrameric, NAD+-de pendent enzyme, loosely associated with the cytoplasmic membrane. Two of the subunits, HoxH and HoxY, are homologous to dimeric [Ni-Fe]-hydrogenases whereas the remaining two subunits, HoxF and HoxU, constitute the diaphorase moiety of the enzyme. There is an evolutionary relationship between the latter two subunits and components of complex I of the respiratory chain, localized in the mitochondrial membrane of eukaryotes (NADH:ubiquinone oxidoreductase) and in the cytoplasmic membrane of prokaryotes (NADH-dehydrogenase I). In cyanobacteria, an oxidation of NADH, catalyzed by NADH-dehydrogenase I, was localized mainly in the cytoplasmic membrane. Until now, only an incomplete version of complex I could be disclosed in cyanobacteria, containing 11 subunits out of 14 which are strictly conserved in other prokaryotes like E. coli. The remaining three subunits, which are homologous to the subunits HoxF and HoxU from Anabaena variabilis, are indispensable for the enzyme activity since they contain the binding sites for NAD +, FMN, and most of the [Fe-S] clusters of complex I. A possible role for the diaphorase subunits as a link between hydrogenase and respiratory chain in the cytoplasmic membrane of cyanobacteria is discussed and a model is proposed, describing an electron input device of complex I, using either H2 or NADH as electron donor. Molecular hydrogen can alternatively be used for the reduction of NAD +, catalyzed by the four subunits of hydrogenase. These alternatives may enable the cyanobacteria to regulate their demand for reductant or ATE depending on the energy balance in the cells. Cyanobacteria possess at least two different hydrogenases catalyzing the reaction H2 +-~ 2 H + + 2 e-. One enzyme, the so-called uptake hydrogenase, is located in thylakoid membranes of heterocysts in Anabaena species and is involved in the photoreduction of NADP ÷ [1]. The uptake hydrogenase catalyzes the recycling of molecular hydrogen produced during N2-fixation by nitrogenase [2]. The uptake hydrogenase genes hupS and hupL, alternatively discussed as accessory genes hupU and hupV (J. Golden, pers. comm.), are subject to DNA rearrangement during heterocyst differentiation [3]. In contrast to the in vitro unidirectional enzyme, the bidirectional ( = reversible) hydrogenase catalyzes both the uptake and the evolution of H2 in vitro. An association to the cytoplasmic membrane was demonstrated by immunogold labeling using polyclonal antibodies raised against the enzyme from the unicellular, non-N2-fixing cyanobacterium Anacystis nidulans [4]. Further experiments, including lysozyme treatment of A. nidulans cells and solubilization of the enzyme from the membrane fraction with low concentrations of the detergent Triton X-100, indicated a peripheral location at the cell membrane [5]. This is in line with the observation that the enzyme is easily detached from the membrane when the cells are broken by sonication, French press treatment, or washing with detergents [1]. Recently, the gene locus of the bidirectional hydrogenase from the heterocystous Anabaena variabilis was identified using a PCR-based approach [6]. Each of four structural genes, hoxE hoxU, hoxY, and hoxH, shows significant sequence homology to the corresponding gene of the tetrameric NAD+-re ducing hydrogenase from A. eutrophus [7]. In contrast to the gene arrangement in the latter organism, the structural genes in A. variabilis are spaced by DNA stretches of about 600-1000 bp in length, two of them possibly encoding proteins of unknown functions, not present in any other hydrogenase gene cluster [8]. Recently, a light-independent NAD +reduction and NADH-dependent H2 formation, both catalyzed by the bidirectional hydrogenase, were demonstrated in crude extracts from A. niduIans [9], corroborating the molecular biological data. The specific activity of the NAD+-reduction is low (85 nmol h q mg protein-Z), which is presumably not sufficient for supporting chemoautrophic growth. Therefore, the functional role of the bidirectional hydrogenase in cyanobacteria remains obscure. The sequence characteristics of the four subunits of the bidirectional hydrogenase from A. variabilis, deduced from the DNA sequence, are shown in Fig. 1, depicting the potential cofactors, [Fe-S] cluster binding sites, and consensus sequences, highly conserved in hydrogenases and other [Fe-S] proteins. Conserved motifs are, e.g., nickel-binding sites in the Nterminal and C-terminal parts of HoxH, representing the large subunit of the hydrogenase dimer, as well as four cysteine residues in the small subunit HoxY, coordinating a putative [4Fe-4S] cluster. This iron-sulfur center was shown to be located in the vicinity of the Hz-activating site of the large subunit of hydrogenase from Desulfovibrio gigas [10]. The latter enzyme contains two additional [FeS] clusters, involved in the transfer of electrons to the physiological acceptor cytochrome c3. These two [Fe-S] cluster-binding sites are not observed in the hydrogenases from either A. eutrophus or A. variabilis. The hydrogenase dimer of both enzymes shows the minimal number of [Fe-S] clusters described for a [Ni-Fe]-hydrogenase. The transfer of electrons to the acceptor site, however, appears to require additional iron-sulfur centers which reside on the subunits HoxU and

Specificity of nun and gypsy moth sexual communication through multiple-component pheromone blends

Abstract: The nun moth [NM; Lymantria monacha (L.)] in Europe and the gypsy moth [GM; L. dispar (L.)] in Europe and North America are most important defoliators of coniferous and decidious forests, respectively [1, 2]. For sexual communication GM and NM females produce the pheromone disparlure [3-6] ; NM and GM males respond to the (+)-disparlure enantiomer [(7R, 8S)-cis-7,8-epoxy-2-methyloctadecane] as a single attractive but unspecific pheromone component [7-11] . Reanalysis of female NM sex pheromone extract by gas chromatographic-electroantennographic detection (GC-EAD [121; Fig. 1), and field tests of candidate pheromone components revealed a multiple-component NM sex pheromone. In the Czech Republic a ternary blend of (+)-disparlure, (7R, 8S)-cis-7,8-epoxy-octadecane [termed here (+)-monachalure] and 2-methyl-Z7-octadecene at a 10 :10 :1 ratio synergistically attracted NM males and was ten times more attractive than previously known (+)-disparlure (Fig. 2). Three epoxide [(-)-disparlure, (+)and (-)-monachalure] and two hydrocarbon volatile components [2-methyl-Z7-octadecene and Z7-octadecene] synergistically prevented crosS-attraction of coseasonal GM males and imparted specificity to NM sexual communication (Fig. 3). Identification of cis-7,8-epoxy-3-methylnonadecane as a second pheromone component in female GM, attracting GM but not NM males, provided the first evidence for species-specific pheromone components also in GM. Future use of multiple-component synthetic pheromone lures will allow highly sensitive and species-specific monitoring of NM and GM populations.

Hygroreceptors in insects and a spider : humidity transduction models

Abstract: The model most favored in insect hygroreceptors for humidity transduction resembles a mechanical hygrometer. It envisions the humidity-dependent swelling or shrinking of hygroscopic structures belonging to the sensillum as governing dendrite activity. This model, however, is at variance with both the organization and the chemical sensitivity of the hygroreceptive sensilla of Cupiennius salei, a wandering spider. Activity changes in these sensilla fit better into an electrochemical concentration model in which humidity would control the concentration of the electrolytes surrounding the dendrites of the hygroreceptors and thus govern their responses. The situation in Cupiennius, therefore, places models for hygroreception in a broader context and also leads to questions concerning their feasibility elsewhere. I nsect hygroreceptors appear to be restricted mainly to a small number of sensilla on the antennae. There they associate in antagonistic pairs (a moist cell and a dry cell) with a thermoreceptor (for reviews of insects, see [2, 3, 21]). The situation in the tarsal organ of the wandering spider, Cupiennius salei, is somewhat similar [9]. The antagonistic hygroreceptors are present here, too, as are also thermoreceptors. These, however, are not cold receptors as with insects, but warm receptors. Externally the hygro-thermoreceptive sensilla of Cupiennius resemble those of insects. All can be broadly classed as peg-like cuticular protuberances, and most possess an apical pore that is filled with electron-dense material. In insects they tend to be stubby and rather conical with rounded tips, or with caps like mushrooms. To the first group belong sensilla coeloconica (in Carausius morosus, Fig. 1 D [5], also in Locusta migratoria, Fig. 1 C [4]) and s. styloconica (in the moth, Bombyx mori, Fig. 1E [22, 23, 26, 27]; also in the saturniid, Antheraea pernyi [12, 38]; and in the noctuid, Mamestra brassicae [8]). To the second group belong sensilla capitula (in Periplaneta americana, Fig. l A [31, 33]) and s. coelocapitula (in Apis mellifera, Fig. 1 B [34, 36]). In Cupiennius, the hygro-thermoreceptive sensilla in the tarsal organ resemble short, conical nipples (Fig. 1 F). As with insects, these, too, lack the columns of pores in the side walls common to olfactory sensilla. Perhaps quite significantly, the dendritic outer segments of their sensory cells are not only coextensive. In contrast to those of insects, they reach right up the lumen of the sensillum to the apical pore ([6]; for insects, see citations above). There is also a further difference: the hygroreceptors in the sensilla of the tarsal organ can also be stimulated by vapors from several very reactive and volatile substances (ammonia, short-chain aliphatic amines, formic and acetic acids [9]).

Circadian Rhythms and Protein Turnover: The Effect of Temperature on the Period Lengths of Clock Mutants Simulated by the Goodwin Oscillator

Abstract: Recent reports that the circadian clock in both Drosophila and Neurospora consists of a negative feedback loop between clock gene (per, frq) activity and amount of clock protein make the Goodwin oscillator a timely model for circadian rhythms. This model is characterized by a negative feedback loop in the clock gene expression with synthesis/degradation reactions associated with each of the intermediates in the loop. The model predicts that predominantly degradation processes of clock mRNA or clock protein control the circadian period and temperature compensation. Assuming a turnover homeostasis of the clock protein, the model explains temperature effects on period length in per and frq mutants. Recent results obtained in Drosophila [1] and Neurospora [2] show that the circadian clock consists basically of a negative feedback loop. This makes the Goodwin model [3, 4] (Fig. 1) and related oscillators [5] useful models for kinetic studies of circadian rhythms. The Goodwin oscillator shows many properties also observed in circadian clocks, such as temperature compensation [6, 7], phase response curves for temperature steps and pulses, and entrainment by tern-

Plankton ecology: The past two decades of progress

Abstract: This is a selected account of recent developments in plankton ecology. The examples have been chosen for their degree of innovation during the past two decades and for their general ecological importance. They range from plankton autecology over interactions between populations to community ecology. The autecology of plankton is represented by the hydromechanics of plankton (the problem of life in a viscous environment) and by the nutritional ecology of phyto- and zooplankton. Population level studies are represented by competition, herbivory (grazing), and zooplankton responses to predation. Community ecology is represented by the debate about bottom- up vs. top-down control of community organization, by the PEG model of seasonal plankton succession, and by the recent discovery of the microbial food web.

Olfactory conditioning in the moth Heliothis virescens

Abstract: In kepidoptera, olfactory signals are important in finding host plants for oviposition or for feeding (nectar sources), as has been shown by numerous behavioral observations with plant extracts or artificial odor mixtures [1]. However, it is unclear whether the responses to plant odors are exclusively innate or depend as well on experience. In the case of bees, it is well known that they are good learners of an odor [21. Like bees, the moths Heliothis virescens and Helicoverpa armigera extend their probosces immediately after the tip of the antennae has been touched with a drop of sucrose solution [3]. This reflex was used in classical conditioning experiments with restrained moths to investigate whether H. virescens females and males are able to learn to respond to plant odors. Newly emerged and 1-day-old moths (males and females) from our own culture were used for the experiments. For the time before testing, the animals were given only water. The moths were mounted individually in small plastic holders (Eppendorf vials with cut tips) in such a way that the head with the antennae remained free. Only animals which showed prompt proboscis extension to antennal sucrose stimulation ( 7 0 7 5 % of the moths) were used for experiments. Conditioning experiments were performed in three phases: the preconditioning test, the conditioning procedure, and the test phase. In each phase the animal was placed in an airstream (1ms ~) 10s prior to presentation of the odor stimulus. The preconditioning test with the odor stimulus alone was performed to ascertain whether the animals responded to the test odor before conditioning. The conditioning procedure was as follows: after placing the animal in the airstream, the conditioning stimulus (CS) was presented for 2 s; directly after the end of the CS one antenna was stimulated with a 1 M sucrose solution (unconditioned stimulus, US). The proboscis extension was rewarded with a drop of sucrose, offered on the tip of a glass vial. Two CS-US pairings were presented at a 10-20-s interval, followed by an intertrial interval of 10 rain. After seven replications, the moths were tested with four extinction trials (CS without reward), each with a 10-min intertest interval. After the first extinction trial an air puff with the solvent (50 ~tl hexan on filter paper) was given as a control to check whether the odor stimulus had been learned specifically or whether the moth responded to either the airflow or the solvent. The conditioning experiment was repeated on 2 consequentive days. In the control experiment the CS and US were presented unpaired, with 5-rain intervals between each other. Each time, two CSs and two USs were given. After seven replications, one test with the CS followed. The conditioning stimulus used was a mixture of citronellol, pentan-l-ol, and a-pinene (0.5 nl, 1 M, 1 ~tl on filter paper, respectively). All compounds are known to be ingredients of cotton bud scent [4], which is attractive to H. virescens males and females [5]. There are two reasons why a mixture of compounds was used for the learning experiments instead of single compounds. Firstly, it is known from behavioral studies that mixtures are more attractive than single compounds [6], and secondly, mixtures are more similar to the natural situation than single compounds. For statistical evaluation of the results the 2 × 2 table chi2-test [7] was used. Statistical evaluation was done for the first extinction trial, unless stated otherwise. The conditioning experiments showed that both sexes were able to learn to respond to floral odors. In Fig. 1 a (females) and Fig. I b (males) the behavior of the test groups is plotted as the percentage of animals responding to the CS on each presentation. After conditioning in seven trials (of two CS-US pairings each), 67°7o of the females showed proboscis extension to the first extinction trial on the 1st day and 65% on the 2rid day (Fig. l a, Test No. 1). Both percentages were different from zero (control experiment) with a statistical significance of a = 0.001 (2x2 table chi2-test). In females, the response level to the odor mixture on the 1st day was the same as that on the 2nd day. Differences were observed in the course of acquisition. Acquisition on the 1st day was slower than on the 2nd day. On the 1st day, a maximum response level was reached by the sixth conditioning trial, whereas on the 2nd day, the same level was reached by the fourth replication. The moths responding on the 2nd day were the same individuals as had responded on the 1st day. H. virescens males were poorer learners than the females. On the first conditioning day, only 38O7o of t h e males were successfully conditioned, statistically significant at a = 0.01 (Fig. l b, Test No. 1). Differences among responses in males and females were statistically significant at a = 0.05 (2x2 table chiZ-test). On the 2nd day, the response level in males reached 58%, which is quite similar to the values found in the females. On the 2rid day, the same animals responded as on the 1st day, with the addition of some new ones. The differences between the responses during the seventh acquisition trial and the first test on the 1st as well as on the 2nd day were statistically not significant (2 x 2 table chi2-test). In control experiments, the unpaired training situation produced no or negligible response (one response in one female) in both sexes (Fig. 1, C S U S unpaired). Memory for the odor was tested by repeated extinction trials. No extinction was found in females during the first three tests (10-min intertest interval), and a marked decline was found by the fourth test. In male moths a much faster extinction process was observed. Some animals in both sexes remembered the learned odor 24 h after conditioning. Five females out of 23 (statistically significant at a = 0.01) and three

Molecular biology of plant mitochondria

Abstract: Mitochondrial genomes of higher plants are more than ten times as large as mitochondrial DNAs in animals. The size difference is explained by additional genes, by internal duplications, and by integrated nuclear and chloroplast sequences. The approximately 100 protein-coding genes in plant mitochondria are transcribed from scattered promoters with unique structures. After transcription, the primary information of mRNA and tRNA precursors is altered by RNA editing, which changes up to 15% of the codon identities. RNA editing is observed in mitochondria of almost all land plants, but has not been found in algae, suggesting that this process became established during the evolutionary transition to land plants. Maturation of mitochondrial RNAs further involves splicing of intervening sequences in cisand trans-splicing configurations. Excision of some of these introns appears to require RNA editing in the intron sequences. Nonlethal mutations in mitochondrial genes invariably affect pollen maturation and lead to male sterile plants. I n a functionally competent plant cell, coordinated expression of three different genomic compartments is required. Whereas animal cells contain genetic information in only two organelles, the nucleus and the mitochondrion [1], plant cells additionally store inherited information in the chloroplast. To understand the interactions between the three different genomes in a plant cell, each of the three compartments must be considered with respect to its coding capacity and the regulation of its expression. Here we summarize current knowledge of the plant mitochondrial information content and its expression. The mitochondrial genome is derived from the genome of a former prokaryote, probably related to the ancestors of the a-subdivision of purple bacteria, which has become embedded in the cytoplasm of the ancestors of eukaryotic cells [2]. Upon integration, parts of the genetic information of the former free-living bacteria became superfluous and were deleted, while other parts moved from the endosymbiont into the nucleus [3]. The nuclear genome thus established its role as the major information storage and retrieval system of the cell. A small part of the genetic information of the endosymbiont, however, was retained in the mitochondrial genome and is still essential for the full physiological and biochemical competence of the cell [2, 3]. Both nuclear and mitochondrial genes often contribute to polyprotein assemblies such as the mitochondrial ribosomes and respiratory-chain complexes, for which expression thus has to be tightly coordinated. The mitochondrial genomes in plants and animals share a basic set of genes encoding components of the mitochondrial translation system and of the respiratory chain of the inner mitochondrial membrane. The much larger mitochondrial genomes of plants additionally contain unique genes with only partially known functions [4-7]. Present investigations are aimed at determining the information content of the

Signal transduction molecules in the rat pineal organ: Ca2+, pCREB, and ICER.

Abstract: The mammalian pineal organ transduces light-dependent neural inputs into a hormonal output. This photoneuroendocrine transduction results in a largely elevated concentration of the pineal hormone melatonin at night. The rhythm in melatonin production and secretion depends on activation and inactivation of transcriptional, translational, and posttranslational mechanisms fundamentally linked to two second messenger systems, the cAMP- and the Ca(2+)-signal transduction pathways. Here we review molecular biological, immunocytochemical, and single-cell imaging studies, which demonstrate a time- and substance-specific activation of these signaling pathways in rat pinealocytes. The data provide a framework for understanding the complex interactions between second messengers (cAMP, Ca2+), transcription factors (CREB, ICER), and their role in regulation of melatonin synthesis. The data have proven the rat pinealocyte to be an interesting model to study transmembrane signaling pathways which may be common to both neuroendocrine and neuronal cells.

Melanin as a visual signal amplifier in male guppies

Abstract: J. Bacteriol. 166, 1128 (1986) 2. Rohde, M., Mayer, E, Hicks, D.B., Krulwich, T.A.: Biochim. Biophys. Acta 985, 233 (1989) 3. Tiedge, H., Sch~fer, G., Mayer, E: Eur. J. Biochem. 132, 37 (1983) 4. Mayer, E, Jussofie, A., Salzmann, M., Lttbben, M., Rohde, M., Gottschalk, G.: J. Baeteriol. 169, 2307 (1987) 5. Reidlinger, J., Mayer, E, Mt~ller, V.: FEBS Lett. 356, 17 (1994) 6. Rohde, M., Mayer, E, Meyer, O.: J. Biol. Chem. 259, 14788 (1984) 7. Rohde, M., Mayer, E, Jacobitz, S., Meyer, O.: FEMS Microbiol. Lett. 28, 141 (1985) 8. D~ikena, P., Rohde, M., Dimroth, P., Mayer, E: ibid. 55, 35 (1988) 9. Rohde, M., D~tkena, P., Mayer, E, Dimroth, P.: FEBS Lett. 195, 280 (1986) 10. Mayer, E, Rohde, M.: Meth. Microbiol. 20, 283 (1988) 11. Mayer, E, Rohde, M., Salzmann, M., Jussofie, A., Gottschalk, G.: J. Bacteriol. 170, 1438 (1988) 12. Mayer, E: ASM News 59, 346 (1993) 13. Mayer, F.: FEMS Microbiol. Rev. 104, 327 (1993) 14. Ossmer, R., Mund, T., Hartzell, P.L., Konheiser, U., Kohring, G.W., Klein, A., Wolf, R.S., Gottschalk, G., Mayer, E: Proc. Nat. Acad. Sci. USA 83, 5789 (1986) 15. Hoppert, M., Mayer, E: FEBS Lett. 267, 33 (1990) 16. Braks, I.J., Hoppert, M., Roge, S., Mayer, E: J. Bacteriol. 176, 7677 (1994) 17. Hoppert, M., Braks, I., Mayer, F.: FEMS Microbiol. Lett. 118, 249 (1994) 18. Mlejnek, K.: Diploma Thesis, Univ. GOttingen 1995 19. Khmelnitsky, Y.L., Kabanov, A.V., Klyaehko, N.L., Levashov, A.V., Martinek, K., in: Structure and Reactivity in Reverse Micelles, p. 230 (M. P. Pileni, ed.). Amsterdam: Elsevier 1989 20. Bianucci, M., Maestro, M., Walde, P.: Chem. Phys. 141, 273 (1990) 21. Khmelnitsky, Y.L., Neverova, I.N., Polyakov, V.I., Grinberg, V.Y., Levashov, A.V., Martinek, K.: Eur. J. Biochem. 190, 155 (1990) 22. Levashov, A.V., Klyachko, N.L., Bogdanova, N.G., Martinek, K.: FEBS Lett. 268, 238 (1990) 23. Seno, M., Sawada, K., Araki, K., Iwamoto, K., Kise, H.: J. Coll. Interf. Sci. 78, 57 (1980) 24. Boicelli, C.A., Conti, E, Giomini, M., Giuliani, A.M.: Chem. Phys. Lett. 89, 490 (1982) 25. Tsujii, K., Sunamoto, J., Fendler, J.H.: Bull. Chem. Soc. Jpn. 56, 2889 (1983) 26. Walde, P., Peng, Q., Fadnavis, N.W., Battistel, E., Luisi, P.L.: Eur. J. Biochem. 173, 40t (1988) 27. Wiggins, P.M.: Microbiol. Rev. 54, 432 (1990) 28. Luisi, P.L., Magid, L.J.\" Crit. Rev. Biochem. 20, 409 (1986) 29. Clegg, J.S.: Am. J. Physiol. 246, R133 (1984) 30. Wiggins, P.M., MacClement, B.A.E.: Int. Rev. Cytol. 108, 303 (1987) 31. Beveridge, T.J.: ASM News 61, 125 (1995)

Iridoid monoterpene biosynthesis in insects: Evidence for a de novo pathway occurring in the defensive glands of Phaedon armoraciae (Chrysomelidae) leaf beetle larvae

Abstract: for technical assistance in the experiments and especially in evaluating the data. We thank M. Ferber and R. Hustert for critical reading of the manuscript. Part of this study was supported by the Deutsche Forschungsgemeinschaft in the program SFB 45 \"Comparative Neurobiology and Behaviour\". 1. Piek T., Spanjer W.: Chemistry and pharmacology of solitary wasp venoms. In: Venoms of the Hymenoptera (T. Pieked.). pp 161-307. London: Academic 1986 2. Steiner, A.: Stinging behaviour of solitary wasps. In: Venoms of the Hymenoptera (T. Piek ed). pp 63-159. London: Academic 1986 3. Gnatzy, W., HeuBlein, R.: Naturwissenschaften 73, 212 (1986) 4. Gnatzy, W., Auton, S., Thier, S.: Prey 5.

Parasites and carotenoid-based signal intensity: How general should the relationship be?

Abstract: Evidence that selection by parasites maintains heritable variation in sexually selected signals (Hamilton-Zuk model) has proved equivocal. Bright individuals do not always have fewer parasites in intraspecific comparisons. Because the lymphocyte-based defence system and the production of some colors used in sexual signaling require carotenoids, we consider a trade-off between defence against parasites and sexual signals. The nature and the sign of the covariance between defence and signal brightness can vary. Depending on carotenoid availability and allocation, and the type of sexual signal, various relationships between parasite load and signal intensity are expected.

Arboreal nest building and ant-garden initiation by a Ponerine ant

Abstract: LEEC-URA CNRS 667, Universit6 Paris XIII , F-93430 Villetaneuse, France system with pruning scissors. In doing so, we minimized the risk of overlooking species due to their small size or discret behavior, or those which, like P. goeldii, are nocturnal. The AGs were not unduly disturbed by this treatment, and we were able to examine them again during our successive visits to French Guiana. Over the totality of the three sites, P. goeldii was the second most frequent species, present in 24.3% of the AGs (n = 460, Table 1). On the plantation, with a level of presence at 27.9%

Object detection by relative motion in freely flying flies

Abstract: The ability to detect objects and to distinguish them from the background (figure-ground discrimination) is essential if an animal is to navigate successfully in its environment. When an animal moves in the environment, the resulting mot ion of the retinal image carries powerful cues that can be used to extract informat ion about the three-dimensional structure of the visual surround (e.g. [1]). Small animals that lack the interocular separation or visual acuity necessary fol z stereopsis [2] can still obtain depth informat ion if they exploit the image mot ion cues generated by their own motion. As an example, consider the situation of an insect flying over a meadow with flowers raised above the grass. When the insect passes a flower, the image of the flower moves more rapidly across the retina than that of the ground, because the flower is closer to the animal ' s eye. Thus, relative image mot ion can be used to distinguish the flower from its, immediate background, even if other cues such as differences in colour, brightness or texture are weak or absent. The problem of f igure-ground discriminat ion by relative mot ion has been studied intensively in the fly [3]. Experiments on tethered flying flies inside a rotating drum have revealed that flies are able to detect a stripe (\"object\") covered with the same texture as the interior of the drum (\"background\") when the stripe moves relative to the background, the only available cue to detect the stripe being the relative motion between stripe and drum [4]. Moreover, electrophysiological studies have led to the characterization of a neuronal circuitry which may underlie figure-ground discrimination by r e l a -

Subtropical Eastern Atlantic climate during the Eemian

Abstract: Rapid oscillations have been found in the oxygen isotope record of the GRIP ice core during the Eemian/Marine oxygen Isotope Stage (MIS) 5e [1]. Terrestrial climate records suggest that these variations may indeed be indicative of rapid climate changes during this period [2,3]. In contrast, the GISP2 ice core [4] and some Atlantic deep-sea records [5, 6] suggest no such variations, while other deep-sea records suggest that there was an intra-Eemian freshening and cooling of the Norwegian Sea and North East Atlantic [7]. We present here an extremely highresolution set of marine proxies from the low-latitude East Atlantic Margin (ODP Site 658), which suggest that, in general, MIS 5 e was climatically very stable. However, we observe that MIS 5 e contains one significant short cold spell (<400 years), which is marked by a reduced upper North Atlantic deep water ventilation. Despite no direct age correlation being possible, this cold spell may reflect the cause of the cold interval implied by the European terrestrial records [2, 3]. This brief cold spell did not affect the overall stability of MIS 5 e. Our records are also incompatible with those of the GRIP ice core record [1], supporting the suggestion that the GRIP Eemain record has been altered by ice tectonics [4, 8, 9]. The climate records of the GRIP [1] and GISP2 [4] ice cores recovered from

Olefin inhibitor of gypsy moth,Lymantria dispar, is a synergistic pheromone component of nun moth,L. monacha

Abstract: the vasotocinergic hypothalamo-hypophysial system controls the salt-water balance in fish. One target organ of vasotocin is the kidney which, in fish, serves mainly for the excretion of water, Mg 2+, and SO42ions; among other hormones, vasotocin influences these renal processes [11, 12]. In addition, the epithelia of the gills, which represent the most important organs for exchange of monovalent ions, NH 3, and NH4 +, are an important target for vasotocin. In various teleost species they contain vasotocin receptors whose binding capacity is correlated positively with salinity [13, 14].

Collection of extrafloral trichome secretions for nest wool impregnation in the solitary bee Anthidium manicatum

Abstract: 1. Ule, E.: Bot. Jahrb. Syst. Pflanzengesch. Pflanzengeog. 30, 45 (1901) 2. Wheeler, W.M.: Ecology 2, 89 (1921) 3. Belin-Depoux, M.: Terre Vie 46, i (1991) 4. Kleinfeldt, S.E.: Ecology 59, 449 (1978) 5. Davidson, D. W., Epstein, W.W., in: Vascular Plants as Epiphytes, p. 200 (U. Lattge, ed.). New York: Springer 1989 6. Yu, D.W.: Biotropica 26, 222 (1994) 7. Davidson, D.W.: Ecology 69, 1138 (1988) 8. Peeters, C., HOlldobler, B., Moffett, M., Musthak All, T.M.: Ins. Soc. 41, 211 (1994) 9. Kteinfeldt, S.E., in: Insects and the Plant Surface, p. 283 (J.B. Southwood, ed.). London: Arnold 1986 10. Mann, W.M.: Psyche 19, 36 (1912) 11. Benson, W.W., in: Amazon Ant-Plants, p. 239 (G.H. Prance, T.E. Lovejoy, eds.). Oxford: Pergamon 1985 12. Dejean, A., Corbara, B., Snelling, R.R., Belin-Depoux, M.: Acta Bot. Gall. (in press) 13. Corbara, B., Dejean, A.: Actes Coll. Ins. Soc. (in press) 14. Verhaagh, M.: Andrias 13, 215 (1994) i5. Madison, M.: Selbyana 2, 1 (1977) 16. Madison, M.: ibid. 5, 107 (1979) 17. Orivel, J., Errard, C., Dejean, A.: Actes Coll. Ins. Soc. (accepted) 18. Seidel, J.L., Epstein, W.W., Davidson, D.W.: J. Chem. Ecol. 16, 1791 (1990)