The ocelli control the flight course in honeybees

Abstract Fully-sighted honeybees and bees with all ocelli occluded were trained to fly through an arena to arrive at a feeding place. After training, the bees were exposed to side-light flashes during their feeding flights. The flight paths were recorded on video and analysed frame by frame at 40 ms intervals with reference to the main parameters, the coordinates of the thorax and the yaw angle of the bee. Course angles, translational course velocities and accelerations were calculated, and the responses to side light flashes evaluated with respect to 'on' and 'off.
Immediately after light on, fully-sighted bees respond slightly positively by yawing and flying toward the side light. Bees in which all ocelli are occluded are greatly disturbed and respond with negative yawing and flight path directions.
The ocelli apparently help to control phototactic alertness in the bee. They determine whether phototactic orienting or pattern-induced orienting behaviour is more important in a particular state of motivation. They help to minimize the level of disturbance in flight course control, obviously by activating a neuronal circuit with comparator attributes. It is assumed that this kind of compensation or suppression of phototactically guided reflexes occurs only for a few 100 ms. Consequently, the biological significance of light flashes shorter than 400 ms is very slight.
Fully-sighted bees decelerate strongly when a side light is switched on. Bees in which the ocelli are occluded behave less cautiously: they generally fly faster and need more reaction time. Thus, the ocelli help the bee to react photokinetically to photic stimuli in a much shorter time than do the compound eyes alone.     

Cell Adhesion as a Basis of Pattern in Embryonic Development

The development of the modern methodologies of cell biologyin the fifties and sixties and of molecular biology in the seventiesand eighties has led to a reductionist view of embryonic developmentthat centers on the cell and the gene as the functional unitsof development. The functional units in most inductive and morphogeneticprocesses in the embryo are not single cells, however, but ratherare collectives of interacting cells that give rise to the tissuesand organs. Can these methodological developments reconcilea molecular analysis with the fact that form arises epigeneticallyfrom the increasing number of embryonic cells during development?To answer this question one must link genetic regulation tomechanochemical processes that coordinate cell division, cellmovement and cell death. Recent studies of cell adhesion suggestthat one such link is provided by cell adhesion molecules (CAMs)that mediate cell-cell binding. These studies suggest that CAMsare involved in defining cell collectives and their bordersas they interact during inductive events in morphogenesis. AlthoughCAMs cannot be considered the "cause" of induction, they playkey roles among the complex causal chains of inductive interactionsinvolving hormones and growth-factors, extracellular matrixcomponents and cellular receptors. We provide here a brief summaryof modern developments in the field centered about the functionof CAMs in morphogenesis and using recent experimental resultsin the developing feather as a paradigmatic example.     

Factors affecting aphid acquisition and transmission of soybean mosaic virus

Myzus persicae transmitted soybean mosaic virus (SMV) most efficiently following 30 or 60 s acquisition probes on infected plants. There were no differences in susceptibility to SMV infection of soybean plants 1 to 12 wk old, but symptoms were more severe in plants inoculated when young than when old. Soybeans inoculated between developmental stages R3 and R6 only showed yellowish-brown blotching on one or more leaves. There were no observable differences in the time of appearance or type of symptoms shown by soybean seedlings inoculated either by sap or by aphids; infected plants became acquisition hosts for aphids 5–6 days after inoculation. There was no change in the efficiency with which M. persicae transmitted SMV from source plants up to 18 wk after inoculation. M. persicae transmitted SMV from leaves of field-grown soybeans when plants were inoculated at developmental stages V6, R2, and R3 and tested as sources 57–74 days after inoculation but not from plants inoculated at R5 and tested as sources 14 to 32 days after inoculation. M. persicae acquired SMV from soybean buds, flowers, green bean pods, and unifoliolate, trifoliolate, and senescent leaves. Middle-aged and deformed leaves were better sources of the virus than buds, unfolding and old symptomless leaves. The results are being incorporated into a computer model of SMV epidemiology.     

Role of the Galactose Binding Protein in Chemotaxis of <Emphasis Type="Italic">Escherichia coli</Emphasis> toward Galactose

The galactose binding protein is the part of the galactose chemoreceptor which recognizes the attractants galactose, glucose and a number of structurally related chemicals.     

Tricarboxylic Acid Cycle Enzymes in Tetrahymena pyriformis after Infection of the Cockroach Periplaneta americana1

SYNOPSIS. Activities of enzymes of the tricarboxylic acid cycle in extracts of Tetrahymena pyriformis S, axenically recovered after living in the hemocoel of female cockroaches Periplaneta americana for 48 hr, were compared with activities in ciliates not exposed to the cockroach. Malic dehydrogenase activity was depressed after recovery from the cockroach; isocitric and succinic dehydrogenases and α-ketoglutaric oxidase activities were unchanged. Citrate synthetase activity was increased, and pyruvi oxidase activity decreased, after ciliates had been in the cockroach. These alterations persisted for several hundred generations after recovery from the insect.     

INHIBITION OF CATALASE IN MESENCEPHALIC CULTURES BY l-DOPA AND DOPAMINE

Catalase activity in cell cultures of fetal rat mesencephalon was decreased by 42 and 50%, respectively, after exposure to l-3,4-dihydroxyphenylalanine (l-DOPA, 100 μM) or dopamine (100 μM) for 48 h. Catalase activity was also decreased 21% by 10 μM hydroquinone. Ascorbic acid (200 μM), an agent that suppresses the autoxidation of l-DOPA and dopamine, blocked the anti-catalase effect of l-DOPA, but not that of dopamine. Inhibitors of the A and B forms of monoamine oxidase (20 μM clorgyline plus 20 μM pargyline) had no effect on the anti-catalase action of either l-DOPA or dopamine. The latter results suggest that products of the oxidative deamination of dopamine by monoamine oxidase are not involved in the suppression of catalase activity. However, autoxidation reactions of l-DOPA may play a role since ascorbate suppressed the anti-catalase effect of l-DOPA. On the contrary, the basis for the failure of ascorbate to similarly block the anti-catalase effect of dopamine is uncertain. l-DOPA and dopamine (25 μM) also inhibited crystalline catalase in solution after incubation for 1 h at neutral pH (40–50% inhibition). Inhibition was blocked by 0.45 M ethanol, indicating a need for autoxidation and the formation of compound II, which is an enzymatically inactive form of catalase. The ability to model the enzyme inhibition in purely chemical experiments indicates a probable mechanism for loss of enzymatic activity in cell cultures. Inhibition of catalase may contribute to cell damage during incubation of cultures with l-DOPA, dopamine, or other autoxidizable compounds. Copyright © 1996 Elsevier Science Ltd     

Molecular Characterization of the D Surface Protein Gene Subfamily in Paramecium tetraurelia

ABSTRACT. When Paramecium tetraurelia expresses the D serotype, detectable by serum tests, high molecular mRNA could be isolated, which corresponds to the molecular mass of the D surface protein. Using this D specific mRNA as a probe for screenings in different genomic libraries a subfamily of five very similar genes was found, named α-51D, _γ1-51D, _γ2-51D, δ-51D and ε-51D. Each of them is about 8-kb long, they show regions of identity to each other, and there is no evidence that any are defective genes or pseudogenes. Up to now serotype D is the only known serotype showing this phenomenon. Another novel feature is that two of the D isogenes are closely linked. The sequence for the entire coding region of the α-51D gene has been determined, as well as the upstream and downstream noncoding regions. Its deduced amino acid sequence shows the same characteristic cysteine periodicity displayed by all other immobilization antigen (i-ag) genes from Paramecium. However, in contrast to most other such genes, tandem repeats are missing from the 7599-bp long coding region of the α-51D gene. When the sequences of the type 51D genes are compared to each other, the similarity is very high and extends to coding as well as to noncoding regions. Similarity within noncoding regions is usually only observed for allelic i-ag genes. We conclude that the type D genes constitute a family of isogenes that are nonallelic. They contain slightly different consensus sequences with possible functions as regulatory regions.     

The Mechanism of Geoperception in Lentil Roots

The sediment of the amyloplasts in the statocytes of lentilroots was analysed in two different samples of seedlings. Theroots of the first sample (HP) were grown in a horizatal position,whereas thoes of the second sample (VP+20) were grown in a horizontalposition and then exposure to give a response). It is demonstratedthat the statolish can almost enter into contact with the plasmamembrane lining the longitudinal wall of the statocytes of theHP sample. However, these organelles in the VP+20 sample areable to provoke a geotropic stimulation though they are sedimentedat a distance of 0.1350–0.2600 µm from the plasmalemma.From these data it is concluded that the cytoplasmic structureswhich may play a role in the geotropic stimulation are: (1)the endoplasmic reticulum located along the longitudianl wallof the statocytes and (2) the microtubules or the plasmalemmaif the action of the statoliths is transmitted by the parietalcytoplasm. The large aggregations of endoplasmic reticulum whichare situated in the distal part of the central root cap cellswould not have any role in the perception of gravity by roots.These results are discussed in the light of recent work showingthe action of a growth inibitor in the geotropic reaction ofroots.     

Species-Recognition in the Field Cricket, Teleogryllus oceanicus: Behavioral and Neural Mechanisms

SYNOPSIS. Field crickets depend on acoustic organs to detectthe presence of potential predators as well as conspecific crickets.Predators are recognized largely on the basis of spectral frequenciesthat are contained in their acoustic signals. Puffs of air andvery low frequencies activate a cricket's cereal receptors andultrasonic frequencies activate their tympanal organs. Bothof these acoustic stimuli release "escape behavior," in theform of evasive movements. An identified neuron sensitive toultrasound is described. Crickets recognize singing conspecificsby both frequency and temporal properties of cricket songs;however species recognition requires specific temporal informationin calling songs. While previous studies have emphasized therole of songs on female behavior, males also recognize conspecificsongs; sexual differences in recognition behavior occur.