Visually induced height orientation of the fly Musca domestica

The visually controlled height orientation of fixed flying flies (Musca domestica) was investigated. The flight lift force measured by a transducer drives the vertical motion of a panorama. The dynamical conditions of the free flight are electronically simulated for the fly with respect to this degree of freedom of motion. In most of the experimentally investigated cases the panorama consists of a horizontally oriented narrow dark stripe on a bright background. The fly orientates with respect to the stripe, transporting it into a stable fixation position just below the equatorial plane of its compound eyes. It is experimentally demonstrated that the formalism of the linearized theory of the pattern induced flight orientation — Poggio and Reichardt (1973a) — can be applied to describe the height orientation of the fly. The experimental evidence concerning the simultaneous perception of stripes moving in a well defined manner in front of each of the two compound eyes is consistent with the hypothesis that the two halves of the visual system are perceptually additive.     

Optomotor reaction and fixation of walking colorado beetles (Coleoptera: Chrysomelidae): Course control aspects

The paths of Colorado beetles (Leptinotarsa decemlineata Say)in a featureless environment are circular. This behavior is explained by an internal asymmetry. To stabilize the path, the fixation reaction or the optomotor response must work against this asymmetry. The turning behavior was examined in stationary patterns of vertical stripes different at spatial wavelengths (). The internal asymmetry was tested in a horizontally striped pattern. A stable fixation reaction was found only for 120 °. The results suggest that larger intrinsic turning tendencies shifts the stable point of the fixation reaction. The same vertically striped patterns were rotated to examine the following reaction of the beetle. It is concluded that the fixation component of the response of these insects, in particular, does not differ in the two situations.     

Visual edge fixation and negative phototaxis in the mealworm beetle Tenebrio molitor

The visual fixation response of the mealworm beetle Tenebrio molitor, elicited by black stripes upon a bright background is studied in an arena and by means of the Y-maze technique. In the arena the distribution n() of the beetle's angular position is measured at different distances from the centre, which is also the starting point. If the black stripe is narrow, the maximum of n() coincides with the centre of the stripe (centre-fixation Figure 1a). If one half of the panorama is black, the distribution n() has two maxima, which are near the borders between the black and white regions (edge-fixation Figure 1b). In the Y-maze experiments the beetle is tethered, but its head is free to move. The black stripes elicit turning tendencies F(), the strength of which depends upon the angular distance between the centre of the stripe and the animal's body axis. If the black stripe is narrow, the stable zero crossing of F() lies at =0, in agreement with the centre fixation in the arena (Fig. 3). If the stripe is 180° wide, two stable zero crossings are obtained near the border lines between the black and white regions, provided that the panorama is rotated around the animal with an angular velocity w larger than about 0.08°/s (Fig. 4). Below this value of w only one stable zero crossing at =0 exists (Fig. 6). Thus the tethered beetle's response underlies a transition between centre resp. edge fixation at a critical angular velocity of the drum. Some implications of this surprising phenomenon with respect to the mechanism of fixation and negative phototaxis are discussed but at present it is considered primarily a challenge for further investigation.Supported in part by Deutsche Forschungsgemeinschaft     

Knotenbau und Blattgrundvaskularisation bei einigenGentianaceae

As a rule,Gentianaceae exhibit a double unilacunar nodal pattern. Upon leaving the lacun, the complex leaf trace divides first into three branches, and then into five or more bundles which become the leaf veins. OnlyGentiana lutea (andG. punctata) as well asMenyanthes trifoliata differ from all other species investigated by their multilacunar nodes. BothCentaurium andOrphium within the cortex form a completely closed bundle ring around the nodal flanks from smaller bundles which depart from the lateral branches of the complex leaf traces.

     

Population Dynamics of Daphnia Hyalina Leydig (Crustacea: Cladocera) in a Productive and an Unproductive Lake in the English Lake District

The population dynamics of Daphnia hyalina Leydig in a productive lake, Esthwaite Water, and an unproductive lake, Buttermere, in the English Lake District have been compared. The winter is passed as resting eggs in the bottom sediments in Buttermere and as free-swimming individuals in the planktonic zone in Esthwaite Water. In Esthwaite Water seasonal periodicity was characterised by maxima in spring and autumn and a minimum in summer; in Buttermere, there was no spring maximum and the first increase in population density was in summer. Population densities were higher and adult females were larger and laid more eggs per clutch in Esthwaite Water than in Buttermere. In each lake males became numerous in autumn. Observed rates of population increase, r and calculated birth rates, b and death rates d were nearly always higher in Esthwaite Water than in Buttermere.     

Selection of a Potent Bacillus licheniformis Strain Producing Thermostable Amylase

A highly potent strain of Bacillus licheniformis 103 that synthesized thermostable -amylase with temperature and pH optima of 90–95°C and 6.0–8.5, respectively, was obtained by mutagenesis and selection. The composition of fermentation media and conditions for submerged cultivation of the producer were optimized. -Amylase whose activity reached 260 U/ml was obtained in laboratory fermenters.     

Configurational prey-selection by individual experience in the toadBufo bufo

Summary The habituation method was used to investigate the toad's ability to discriminate between two dimensional prey dummies of different shapes and patterns: If immediately following habituation of the prey-catching orienting behavior to a dummy form A, prey-catching responses are elicited when another form B is presented, it can be concluded that the toad is able to discriminate between the two patterns. The results show that toads are able to discern detailed structures within the outline limits of a 5 mm× 20 mm worm-like shape, on the basis of individual experience (stimulus specific habituation). In particular the results demonstrate that triangular stimulus patterns moved with a horizontal acute angle leading increase the releasing value of prey features whereas separate additional dots moved simultaneously may reduce the prey features of an optimal prey dummy. Dots, stripes and acute angles obviously have a significant effect in theexperience governed pattern discrimination of prey for toadsBufo bufo.Supported by grants of the Deutsche Forschungsgemeinschaft Ew 7/6     

Factors modulating differentiation of spores: Characterization of mutants defective in sporulation in the cyanobacterium Anabaena doliolum (AdS strain)

Summary Mutants of Anabaena doliolum (AdS strain) altered with respect to the time of initiation and degree of sporulation were isolated following mutagenesis with N-methyl-N-nitro-N-nitrosoguanidine and hydroxylamine. The non-sporulating mutant showed a high phycocyanin (Pc): chlorophyll a (chl a) ratio (ca. 7.2) as compared to sporulating strains (Pc:chl a, 4.7–5.3). Also this strain seemed to have higher RNA pools per unit of genomic material as reflected in a higher RNA:DNA ratio. The data suggest that degradaton of phycocyanin and controlled RNA synthesis are prerequisites for sporulation. Mutants exhibiting non-sporulation and delayed initiation of sporulation accumulated more nitrogen through nitrogen fixation, probably indicating nitrogenase function over an extended vegetative phase.     

Head movements of the mealworm beetle Tenebrio molitor

Tethered walking imagines of the mealworm beetle Tenebrio molitor wave their heads in random fashion. If a periodic pattern of vertical black and white stripes is rotated around the animal a regular nystagmic head movement is superimposed upon the random waving, the frequency of the latter equals the contrast frequency within large ranges of the angular velocity of the pattern. The nystagmus is inverted: After a short period of tracking, during which the angular velocity of the head is the same as that of the panorama, the head returns slowly toward its normal position according to an exponential-like function. Resting animals do not wave their heads. However, if the above panorama is rotated, the beetle turns its head in the direction of the movement of the panorama and holds it in a side-way position, as long as the rotation is maintained. The angular position reached depends in the same manner on the angular velocity of the panorama as the turning tendency of walking animals established in open loop experiments using the spherical Y-maze method.     

Features effective in course control during object fixation by walking Colorado beetles

A test paradigm is designed to determine which features of viewed objects (a disk 10° in diameter) are responsible for preferential fixation by Colorado beetles (Leptinotarsa decemlineata). The beetle walks on a locomotion compensator that permits free choice of direction in a visual surround containing three different objects. The beetles use both colour and contrast information in these choice experiments. The preferred colours are yellow and orange; their attractiveness is considerably enhanced when they appear in a pattern with highly contrasting features such as stripes. In its optimal form, the object amounts to a dummy beetle, with a pattern that resembles the markings on the elytra of this species. Since the beetles appear to employ a contact pheromone for sex recognition, the function of orientation to these patterns is unclear. However, the patterns might accelerate the identification of conspecifics or be effective at a distance. The reaction to the dummies is telotactic — that is, the beetles walk towards the dummy. One other object, a 10°-wide black stripe, elicits menotactic orientation, in which the beetle maintains a stable course at an angle to the object.     

Circadian calling behavior of the adult female brown-banded cockroach,Supella longipalpa (F.) (Dictyoptera: Blattellidae)

The diel pattern of pheromone-releasing behavior (calling) of the adult female brown-banded cockroach, Supella longipalpa (F.),was examined. Calling occurs discontinuously throughout most of the scotophase in a 12L: 12D photoperiodic regime. Females exhibited a free-running calling rhythm after transfer to continuous light or dark conditions. Shifts in the temporal pattern of calling following changes in the timing of the photoperiodic cues indicated that lights-off is the Zeitgeber. Studies of insects under long- and short-day conditions suggest that, although insects within a population may call synchronously or asynchronously, respectively, the duration of an individual's calling bout is innately limited.     

Visual pattern discrimination as an element of the fly's orientation behaviour

Summary The visually guided orientation behaviour of stationarily flying Musca domestica (females) has been investigated. Under such conditions, the flight activity does not influence the visual stimulus (openloop) and the tendency of a fly to orientate towards some visual object can be recorded as a yaw torque reaction (orientation response).—Orientation responses to flickering stripes reveal two different mechanisms of visual integration, namely a local flicker detecting mechanism and a specific kind of dynamic lateral interactions (Figs. 3, 5). The lateral interactions are mediated by a field of interconnections of receptors which are separated by at least 4 to 6 vertical rows of ommatidia (Figs. 3, 8). While stimulation of not more than 3 vertical rows of ommatidia activates only flicker detection, stimuli of more than 6° width may in addition exert an excitatory or an inhibitory influence as a consequence of the associated nonlinear interactions (Figs. 5, 7). The relevance of these lateral interactions for tracking and chasing behaviour is discussed. It is suggested that the fly's visual pattern discrimination rests essentially on these lateral interactions.     

Concurrent measurements of oxygen- and carbon-dioxide exchange during lightflecks inAlocasia macrorrhiza (L.) G. Don

Oxygen and CO₂ exchange were measured concurrently in leaves of shade-grownAlocasia macrorrhiza (L.) G. Don during lightflecks consisting of short periods of high photon flux density (PFD) superimposed on a low-PFD background illumination. Oxygen exchange was measured with a zirconium-oxide ceramic cell in an atmosphere containing 1 600 bar O₂ and 350 bar CO₂. Following an increase in PFD from 10 to 500 mol photons·m^-2·s^-1, O₂ evolution immediately increased to a maximum rate that was about twice as high as the highest CO₂-exchange rates that were observed. Oxygen evolution then decreased over the next 5–10 s to rates equal to the much more slowly increasing rates of CO₂ uptake. When the PFD was decreased at the end of a lightfleck, O₂ evolution decreased nearly instantaneously to the low-PFD rate while CO₂ fixation continued at an elevated rate for about 20 s. When PFD during the lightfleck was at a level that was limiting for steady-state CO₂ exchange, then the O₂-evolution rate was constant during the lightfleck. This observed pattern of O₂ evolution during lightflecks indicated that the maximum rate of electron transport exceeded the maximum rate of CO₂ fixation in these leaves. In noninduced leaves, rates of O₂ evolution for the first fraction of a second were about as high as rates in fully induced leaves, indicating that O₂ evolution and the electron-transport chain are not directly affected by the leaf's induction state. Severalfold differences between induced and noninduced leaves in O₂ evolution during a lightfleck were seen for lightflecks longer than a few seconds where the rate of O₂ evolution appeared to be limited by the utilization of reducing power in CO₂ fixation.Abbreviation PFD photon flux density (of photosynthetically active radiation)     

Adventitious bud formation and shoot development from in vitro leaves of Vitis x Muscadinia hybrids

High levels of regeneration were obtained from young leaves excised from axillary shoots in proliferating nodal cultures of several Vitis x Muscadinia hybrids. Best results were obtained when the explants were cultured on solidified half-strength Murashige and Skoog medium supplemented with 8.9 M 6-benzyladenine and 0.05 M 1-naphthaleneacetic acid. Though variation was observed among the hybrids, the procedure used does not seem to be genotype-specific as all the hybrids and cultivars tested could regenerate. Scanning electron microscopy observations and histological studies carried out during the development of adventitious shoot organogenesis revealed that the promeristem initiation occurred in the outer cell layers near the wounded area of the petiolar stub.Abbreviations BA 6-benzyladenine - NAA 1-naphthaleneacetic acid     

Locomotor response of the goldfish to polarized light and itse-vector

Summary The locomotor orientation of eleven goldfish, 20–25 cm long, was monitored during periods varying between 24 hours and 8 1/2 days, to verify the response to a depolarized and polarized sky, 100 cm in diameter, and to abrupt 90 ° degree rotation of thee-vector. The monitor consisted of a cylindrical tank with 16 peripheral compartments (Fig. 1) to which the fish had free access. Entry into and exit from each compartment was electronically recorded. The distribution of entries, which had no cyclical relationship with the compartments in depolarized light, became significantly symmetrical and bimodal in polarized light with the preferred compartments oriented parallel with thee-vector. Abrupt 90 ° rotation of the vector counter clockwise maintained this relationship during the entire duration of the recordings (up to 17 hours) (Fig. 2). The mean of the orientation angles of the fish on leaving compartments aligned with thee-vector were significantly higher than those from the remaining compartments (Fig. 3). This behavior tended to keep the locomotor orientation parallel with thee-vector as the fish moved between compartments. A strong cyclical relationship between these orientation angles and the compartments of origin was present in polarized but absent in depolarized light. Counter clockwise 90 ° rotation of thee-vector maintained the cyclic behavior of angles but the relationship between the larger means and thee-vector shifted over one or two compartments. This shift disappeared in clockwise rotation. This phenomenon may be due to one of these directions being unnatural. The results demonstrate a pronounced sensitivity and response toe-vector orientation in the goldfish. The sensory mechanism remains unknown.The authors are greatly indebted to Dr. T. H. Waterman for a critical review and discussion of the results here presented.     

Effect of temperature and temperature shifts on growth and branching of a wild type and a temperature sensitive colonial mutant (Cot 1) of Neurospora crassa

Growth of a temperature sensitive colonial mutant (cot 1) of Neurospora crassa was compared with a wild type strain. The hyphal growth unit (the ratio between mycelial length and number of branches) of the wild type was not appreciably altered by temperature and there was a direct relationship between the specific growth rate () of these mycelia and their mean hyphal extension rate (E). The specific growth rate of cot 1 increased by about the same relative amount as the wild type between 15° and 30°C. Cot 1 grew and branched normally at 15° and 25°C but at 30°C the hyphal growth unit and mean hyphal extension rate of the mutant mycelia were reduced. Thus, between 15–30°C the ratio, E/ was constant for the wild type but not for cot 1.The effect of temperature and temperature shifts on extension zone length (Z), extension zone expansion time (Z _i ) and branching of leading hyphae of mature colonies were also studies.It is suggested that branching is governed by a mechanism which regulates the linear growth rate of hyphae; the cot 1 mutation may have a direct effect on wall extension or affect linear growth rate indirectly due to an influence on the transport of precursors to the tip.     

Cytologische Untersuchungen an Nematodengallen

Zusammenfassung Zwei verschiedene Faktoren bewirken die Vergrößerung der Riesenzellen (RZ) in den Gallen des NematodenMeloidogyne arenaria (auf Kakteen und anderen Wirten): die Hypertrophie der wachsenden RZ und die Syncytienbildung (Auflösung trennender Zellwände und Verschmelzung kleinerer Zellen).Parallel mit der Entwicklung des Parasiten durchlaufen die RZ und ihre Kerne vier verschiedene Entwicklungsstadien; währenddessen verändern diese Kerne auf charakteristische Weise ihre Größe, Struktur und Gestalt, parallel damit erhöht sich der Polyploidiegrad (die Charakteristika der einzelnen Stadien sind vom jeweiligen Wirt weitgehend unabhängig): der Umriß wandelt sich vorerst durch starke physiologische Beanspruchung des Kerns, in späteren Stadien durch davon unabhängige Mitosestörungen bzw. durch Spindel- und Plattenverschmelzungen während der synchronen Teilungen in den RZ (bei der CrassulaceeCotyledon treten Mikronuklei auf). Die beiden letztgenannten Vorgänge verursachen die Polyploidisierung sowohl in den RZ als auch in manchen unmittelbar an die RZ anschließenden parenchymatischen Zellen, während das übrige Gewebe weitgehend unbeeinflußt bleibt.Eng mit den genannten Ursachen hängt die sehr variable Zahl der Kerne pro RZ und ihre Struktur zusammen: im Stadium der größten physiologischen Beanspruchung der RZ ist der Kern sehr wolkig, später sind die Chromozentren sehr kompakt. Unabhängig vom jeweiligen Entwicklungsstadium der RZ ist das Chromatin an der Peripherie des Kerns konzentriert. Durch die Ursachen, die zu Polyploidisierung und variablem Umriß führen, kommt es zu wahrscheinlich plasmatischen Einfaltungen und Einschlüssen innerhalb des Kerns.Nicht nur im Gallen-, sondern auch im unbeeinflußten Gewebe zeigen Kerne ab einer bestimmten Größe bzw. eines bestimmten Polyploidiegrades stärker lichtbrechende, nicht oder nur wenig anfärbbare, in ihrer Größe zwar vom Kernvolumen abhängige, doch trotzdem kleine Kugeln (in kleineren Kernen sind sie wahrscheinlich nur wegen ihrer Kleinheit nicht auffindbar). Sie sind nur in Glutaraldehyd-fixiertem Material sichtbar, AE als Fixierungsmittel löst sie auf. Sie befinden sich oft in unmittelbarer Umgebung des Nukleolus und hängen wahrscheinlich ursächlich mit ihm zusammen, aber eine exakte Analyse kann nicht gegeben werden.

---

Summary Two determining factors induce the enlargement of giant cells in galls caused by the root-knot nematode (Meloidogyne arenaria in roots of some Cactaceae and other hosts): hypertrophy of the growing giant cells and formation of syncytia.Corresponding with the evolution of the parasitic larva the giant cells and their nuclei become altered through four different stages; the nuclei change their volume, structure, shape and their degree of polyploidy, independent of the specific host: the contour of the nuclei is altered during the development of the giant cells first by physiological factors, on the other hand — later on — by mitotic inhibition resp. by fusing mitotic spindles or mitotic figures during synchronous mitotic divisions in the giant cells (micronuclei occur inCotyledon, Crassulaceae). Polyploidization is induced by the last two mentioned factors in giant cells as well as in some parenchymatous cells surrounding giant cells.Conditioned by these mentioned factors the number of nuclei per giant cell, their structure and shape are very variable. All nuclei in the giant cells possess a significant feature: accumulation of the chromatin material at the nuclear periphery, while the centre of the nucleus is almost optically empty. This structure occurs also during the stage with the greatest physiological stress. Plasmatical foldings and inclusions occur in some voluminous nuclei, produced by the factors leading to polyploidy resp. to variable shape.Not only in giant cells, but also in normal tissues — if their nuclei have reached a low degree of polyploidy — small, refractioning, poor stainable globules exist (they cannot be seen in small nuclei, probably they are too small): they are often sitting upon the nucleolus and are surely corresponding with him, their exact constitution and origin is unknown. They can only be seen in Glutaraldehyd-fixed material, in acetic-alcohol-fixation they are dissolved.

     

Green thoughts in a green shade

The author gives an autobiographical sketch of his path to chlorophyll research, and describes some results. The discussion is largely focused on long wavelength forms of chlorophyll and how they might be generated by self-assembly. Dimers or oligomers, (Chl)_n, result from coordination interactions between the central magnesium atom of one macrocycle and nucleophilic side chains of another i.e., keto C=OMg in the case of Chl a. Coordination interactions mediated by a water molecule coordinated to Mg in one macrocycle and to a nucleophilic group in another e.g., MgO(H)HO=C keto, form aggregates with very different structures and properties; where more than one strong nucleophile or hydrogen bonding group is present in the chlorophyll, e.g., the formyl group in Chl b, the acetyl group of Bchl a, or the hydroxyethyl group of Bchl c, they may also participate in direct coordination interactions with Mg as well as hydrogen bonding to water coordinated to Mg. The magnetic resonance properties of Chl a/water aggregates have provided the basis for the special pair concept for the primary electron donor in photosynthesis. Structural information derived from small angle neutron scattering studies on chlorophyll aggregates is now providing an experimental basis for comprehensive models that integrate antenna and photoreaction center chlorophyll functions.This article was written at the invitation of Govindjee. It has been authored by a contractor of the U.S. Government under contract No. W-31-109-ENG-38. Accordingly, the U.S. Government retains a non-exclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes.     

The initial reaction velocities of lactate dehydrogenase in various cell types

Summary The initial reaction velocities (v _v ) of lactate dehydrogenase in hepatocytes, cardiac muscle fibres, skeletal (gastrocnemius) muscle fibres, gastric parietal cells, ductal epithelial and acinar cells of the parotid gland, and oocytes were determined, by computer-assisted image analysis, in unfixed sections of these tissues incubated at 37°C on substrate-containing agarose gel films. They were found to fit the equations v _i = a₁A (equation 1) and v _i – v = a₂A (equation 2) reported previously for mouse hepatocytes (Nakae & Stoward, 1993a, b), where v and A are, respectively, the gradients (or steady-state velocities) and the intercepts on the absorbance axis of the linear regression lines of the absorbance (A) of the finalreaction product on incubation times between 1 and 3 min, and a ₁ and a ₂ are constants. Both equations 1 and 2 fitted the observed v _i closely for mouse (a ₁ = 2.7, a ₂ = 2.2) and human (a ₁ = 3.0, a ₂ = 1.9) hepatocytes. However, equation 2 fitted the observed v _i better than equation 1 for mouse cardiac muscle fibres (a ₂ = 1.5), skeletal muscle fibres (a ₂ = 1.2), gastric parietal cells (a ₂ = 1.7), acinar (a ₂ = 1.4) and striated ductal (a ₂ = 2.2) epithelial cells of the parotid gland, and oocytes (a ₂ = 1.6). The values of v _i calculated from the two equations agreed with the observed v _i to within about 11%. They ranged from 105 mole hydrogen equivalents/cm³ cell/min units in hepatocytes to 24 units in parotid acinar cells, but for other cell types they were between 46 and 61 units. These are all considerably higher than values reported previously.     

Effects of cytochalasins on developing frog embryos: protection with l-cysteine and α-d-glucosamine

Summary Cytochalasins A, B and H (CA, CB and CH) brought about cellular disaggregation and mortality in the developing embryos of the frog, Microhyla ornata. All three cytochalasins exhibited a dose-response relationship. CA was the most potent and its effects were significantly reduced by simultaneous additon of l-cysteine, a sulph-hydryl compound. -d-Glucosamine, a precursor of complex macromolecules important in cell adhesion, protected against the effects of CH. The effects of CB, however, were influenced neither by l-cysteine nor by -d-glucosamine. The results revealed differences in the mechanism of action of these three cytochalasins.