Scanning eye movements of the stomatopod crustacean,Neogonodactylus oerstedii,in polarized light fields

ABSTRACT

Stomatopod crustaceans have highly mobile, independently moving compound eyes that are sensitive to both linearly and circularly polarized light. They rotate their eyes to predictable angles when viewing a linearly polarized target, and they scan their eyes frequently to sample the visual field. Angles of scans are roughly perpendicular to the plane of the midband (a set of specialized parallel rows of equatorial ommatidia). We investigated scanning eye movements in one Caribbean stomatopod species (Neogonodactylus oerstedii) in uniform visual fields that were vertically polarized, horizontally polarized, or depolarized. We found that mean eye rotation and scan angles differed significantly among these different treatments. Average scan angles differed by 12°, being more horizontal in a vertically polarized field than in a horizontally polarized one, and also more horizontal in a vertically polarized field than in a depolarized field. Thus, these stomatopods adjusted visual scanning to the polarization of the visual environment.     

Gravitational compensation and the phototropic response of oat coleoptiles

Avena seedlings were germinated and grown while continuously rotated on the horizontal axis of a clinostat. The coleoptiles of these gravity-compensated plants were phototropically more responsive than those of plants rotated on a vertical axis. When the plants were compensated after unilateral irradiation, phototropic curvature of the shoot progressed for the next 6 hours, with the rate of curving decreasing about 3 hours after irradiation. The decrease in rate was less in the plants gravity-compensated before irradiation than in those vertically rotated. In the period 70 to 76 hours after planting, the growth rate of the compensated coleoptiles was significantly less than that of the vertically rotated seedlings. The greater phototropic curvature, the decreased growth rate, and the slower rate of straightening of the curved, compensated shoot can be correlated with several consequences of compensation: an increase in sensitivity to auxin, a lowering of auxin content in the coleoptile tip, and possibly, from an interaction between compensation and phototropic stimulation, an enhanced difference in auxin transport between the illuminated and shaded halves of the unilaterally irradiated shoot.

The phototropic response of the vertically rotated seedling was significantly different from that of the vertical stationary, indicating the importance of vertically rotated controls in clinostat experiments.

     

The determination of the maximal bending angle inPhycomyces sporangiophores

The maximal phototropic bending angle of thePhycomyces sporangiophore (spph) was always smaller than 90° from the vertical. Experimental results, using a clinostat apparatus and both a gravitropic mutant and the wild-type spphs placed vertically or horizontally and illuminated from different directions, revealed that this angle resulted from a balance between a negative gravitropism and a phototropism whose direction (positive or negative) and magnitude depended on the bending angle of the spph, because of the involvement of the optical properties of the spph, probably the ratio of the maximal light-fluence rate between the proximal side (I_P,max) and the distal side (I_D,max) of the spph. Shadowing of the extension zone by the sporangium was estimated to be complete only when the bending angle was larger than 86.4° from the vertical.     

THE PHOTOTROPIC EFFECT OF POLARIZED LIGHT

For the growing cell of Phycomyces, a difference in the phototropic effect of light is described depending on its plane of polarization with reference to the axis of the cell. The difference which is found is primarily due to differences in the reflection losses at the cell surface. The magnitude of the effect approximates that deduced from the theory of phototropism suggested for this system. No specific effect of plane polarized light on the growth processes of the cell need be postulated.     

Differential Growth and Phototropic Bending in Phycomyces

Using present knowledge of the cell's optical and growth mechanisms, a theoretical bending speed of about 5° min.^-1 is calculated for unilateral irradiation by a single beam of normally incident visible light; this figure is of the magnitude found experimentally. Between beams of light opposed at 180°, the resultant bending speed is given by the difference-to-sum ratio of the light intensities of the two beams. Valid comparisons between cells differing in size, growth speed, or optical properties are made by expressing bending speed as a fraction of each cell's bending response to unilateral irradiation. With multiple beams differing in intensity and azimuth, the resultant bending speed follows from vector addition of phototropic components proportional to the flux fraction of each beam. The bending speed in Oehlkers' experiment where a luminous area is the light source also appears compatible with this rule. In such experiments, the bending speed quantitatively matches the scaled asymmetry of the pattern of flux incident upon the cell. Resolution experiments support the assumption that light intensity enters into steady state phototropic formulations as the first power of I.     

Lamp-Lit Bridges as Dual Light-Traps for the Night-Swarming Mayfly,Ephoron virgo: Interaction of Polarized and Unpolarized Light Pollution

Ecological photopollution created by artificial night lighting can alter animal behavior and lead to population declines and biodiversity loss. Polarized light pollution is a second type of photopollution that triggers water-seeking insects to ovisposit on smooth and dark man-made objects, because they simulate the polarization signatures of natural water bodies. We document a case study of the interaction of these two forms of photopollution by conducting observations and experiments near a lamp-lit bridge over the river Danube that attracts mass swarms of the mayfly Ephoron virgo away from the river to oviposit on the asphalt road of the bridge. Millions of mayflies swarmed near bridge-lights for two weeks. We found these swarms to be composed of 99% adult females performing their upstream compensatory flight and were attracted upward toward unpolarized bridge-lamp light, and away from the horizontally polarized light trail of the river. Imaging polarimetry confirmed that the asphalt surface of the bridge was strongly and horizontally polarized, providing a supernormal ovipositional cue to Ephoron virgo, while other parts of the bridge were poor polarizers of lamplight. Collectively, we confirm that Ephoron virgo is independently attracted to both unpolarized and polarized light sources, that both types of photopollution are being produced at the bridge, and that spatial patterns of swarming and oviposition are consistent with evolved behaviors being triggered maladaptively by these two types of light pollution. We suggest solutions to bridge and lighting design that should prevent or mitigate the impacts of such scenarios in the future. The detrimental impacts of such scenarios may extend beyond Ephoron virgo.     

Phototropism in Hypocotyls of Radish: IV. Flank Growth and Lateral Distribution of cis- and trans-Raphanusanins in the First Positive Phototropic Curvature

The first positive phototropic curvature induced by a pulse of unilateral white irradiation (0.1 watt per square meter, 30 seconds) of etiolated and de-etiolated Sakurajima radish (Raphanus sativus var hortensis f. gigantissimus Makino) hypocotyls was analyzed in terms of differential growth and growth inhibitor contents of the hypocotyls. In both etiolated and de-etiolated hypocotyls, the growth rates at the lighted sides were suppressed whereas those at the shaded ones showed no change. De-etiolation treatment induced a larger difference between the growth rates at the lighted and shaded sides of the hypocotyls, resulting in a larger curvature of de-etiolated seedlings than of etiolated ones. The contents of growth inhibitors, cis- and trans-raphanusanins, increased in the lighted but not in the shaded halves of the hypocotyls of etiolated seedlings. In de-etiolated seedlings, the two inhibitors increased due to the de-etiolation treatment. When de-etiolated seedlings were exposed to a pulse of unilateral irradiation the level of the two inhibitors remained high along the lighted side for 1 h following the light pulse, whereas at the shaded side the contents of the inhibitors abruptly decreased upon transfer to the dark, the difference between their amounts in the lighted and shaded sides being larger than in etiolated seedlings. Another growth inhibitor, raphanusamide, did not respond to the phototropic stimulus, although its amounts increased by the de-etiolation treatment. These data suggest that cis- and trans-raphanusanins are involved in the first positive phototropic response of radish hypocotyls, and that de-etiolation magnifies the phototropic response through induction of a larger lateral gradient of the raphanusanins in the hypocotyls by the phototropic stimulus.     

Microwaves affect <Emphasis Type="Italic">Myriophyllum aquaticum</Emphasis> plants differently depending on the wave polarization

Previous studies on microwave exposure on plants have revealed variations in sensitivity of plants to different microwave frequencies, exposure durations, and power intensities. However, the effects of different polarizations of microwaves on plants have not been studied. Therefore, we investigated the effect of horizontally and vertically polarized 2 GHz continuous microwaves on Myriophyllum aquaticum plants at 1.8 W m^-2 power density. The electric potential variation along the vascular tissues were investigated for 1.5 h and growth parameters, pigmentation, and H₂O₂ formation were studied during 48 h microwave exposure. Exposure to horizontally polarized microwaves, decreased standard deviation of electric potential variation and increased H₂O₂ content significantly. Vertically polarized microwaves increased the standard deviation of electric potential variation and photosynthetic pigments significantly. However, none of the polarizations altered growth parameters (shoot length, stem diameter, and internodal length). Thermographic images taken for 1 h continuous microwave exposure did not indicate alteration in the temperature of the plants for both vertical and horizontal polarities.     

CONCERNING THE INFLUENCE OF POLARIZED LIGHT ON THE GROWTH OF SEEDLINGS

While these experiments are not exhaustive, a sufficient number have been made to warrant the statement that the effect of polarized light of the visible spectrum on the growth of various seedlings and See PDF for Structure more particularly on the growth of Lupinus albus is somewhat different from that of non-polarized light. This is especially convincing in view of the results obtained with double sets of plants which were alternately exposed to polarized and non-polarized lights of the same intensities and at the same temperature. In every experiment thus performed the set which was placed in a polarizing chamber grew better. It is, furthermore, interesting to note that the phenomenon above observed did not take place when the seed portion of the plants was protected from light by wrapping with tinfoil. This agrees well with previous findings concerning the action of diastase on starch in polarized light. The above researches will be continued on a more elaborate scale but the results so far obtained are deemed worthy of publication in the form of a preliminary communication at the present time.     

Evidence for a phytochrome-mediated phototropism in etiolated pea seedlings

Entirely etiolated pea seedlings (Pisum sativum, L. cv Alaska) were tested for a phototropic response to short pulses of unilateral blue light. They responded with small curvatures resembling in fluence-dependence and kinetics of development a phytochrome-mediated phototropic response previously described in maize mesocotyls. Irradiations from above with saturating red or far-red light, either immediately before or after the unilateral phototropic stimulus, strongly reduced or eliminated subsequent positive phototropic curvature. Only blue light from above, however, entirely eliminated curvature at all fluences of stimulus. It is concluded that the phototropism is primarily a result of phytochrome action.     

Time-dependent phosphorescence anisotropy measurements of the slow rotational motions of proteins in viscous solution

A method of monitoring slow rotational motions of proteins from the decay of the intrinsic phosphorescence is described. The phosphorescence is excited with a 10-μsec pulse of vertically polarized light from an air gap lamp, and the anisotropy was computed as a function of time from the simultaneously detected vertically and horizontally polarized components of the emission. The approach is illustrated with time-dependent measurements of the anisotropy of the tryptophan phosphorescence of Staphylococcus aureus nuclease, bovine carbonic anhydrase, and liver alcohol dehydrogenase in glycerol-phosphate buffer between ?90 and ?70°C. The temperature- and molecular-weight dependence of the exponential decays in the anisotropy indicate that overall rotation of the proteins is at the origin of the depolarization. The potential of the approach as a probe of the slow rotational motions of proteins in membranes and other macromolecular complexes is stressed.     

Blue and Green Light-Induced Phototropism in Arabidopsis thaliana and Lactuca sativa L. Seedlings

Exposure time-response curves for blue and green light-induced phototropic bending in hypocotyls of Arabidopsis thaliana (L.) Heynh. and Lactuca sativa L. seedlings are presented. These seedlings show significant phototropic sensitivity up to 540 to 550 nanometers. Since wave-lengths longer than 560 nanometers do not induce phototropic bending, it is suggested that the response to 510 to 550 nanometers light is mediated by the specific blue light photoreceptor of phototropism. We advise care in the use of green `safelights' for studies of phototropism.     

Phototropism and polarotropism of primary chloronemata of the moss Physcomitrella patens: responses of mutant strains

The phototropic and polarotropic responses of primary chloronemata grown from germinated minated spores of three mutant strains of the moss, Physcomitrella patens, have been studied and compared with those of the wild-type. The mutants and wild-type show the same qualitative tropic responses but differ with respect to the light conditions under which they are expressed. In both the wild-type and mutants the responses are controlled by phytochrome. In monochromatic red light, at low fluence rates, wild-type primary chloronemata grow positively phototropically in unidirectional light or perpendicular to the electrical vector (E) in polarised light; at high fluence rates growth in unidirectional light is lateral to the incident light or, in polarised light, parallel to E. The mutants, however, show only the lateral phototropic or parallel polarotropic responses at all fluence rates of red light tested. In far-red light, the wild-type primary chloronemata adopt a positive phototropic or a perpendicular polarotropic response; the mutants show the same responses but in a lower percentage of filaments. These results and those at other wavelengths indicate either that the mutants are impaired in their ability to adopt the positive phototropic and perpendicular polarotropic responses or that in the mutants the transition between the “low light” (positive phototropic-perpendicular polarotropic) and the “high light” (lateral phototropic-parallel polarotropic) responses is shifted to a lower photon fluence rate. Possible explanations of this phenotypic difference are discussed.     

THE PHOTOTROPIC EXCITATION OF LIMAX

The photic orientation of Limax creeping geotropically upon a vertical plate is such that the phototropic vector determining the angular deflection β from the vertical path is proportional to log I. This is proved by the fact that with horizontal illumination tan β is directly proportional to log I; with non-horizontal light rays from a small source the ratio See PDF for Equation is directly proportional to log I (where A = the angle between light rays and the path of orientation), the vector diagram of the field of excitation being in this case not a right-angled triangle.     

Light pollution may create demographic traps for nocturnal insects

Light pollution impacts both intra- and inter-specific interactions, such as interactions between mates and predator–prey interactions. In mobile organisms attracted to artificial lights, the effect of light pollution on these interactions may be intensified. If organisms are repelled by artificial lights, effects of light pollution on intra- and inter-specific interactions may be diminished as organisms move away. However, organisms repelled by artificial lights would likely lose suitable habitat as light pollution expands. Thus, we investigated how light pollution affects both net attraction or repulsion of organisms and effects on intra- and inter-specific interactions. In manipulative field studies using fireflies, we found that Photuris versicolor and Photinus pyralis fireflies were lured to artificial (LED) light at night and that both species were less likely to engage in courtship dialogues (bioluminescent flashing) in light-polluted field plots. Light pollution also lowered the mating success of P. pyralis. P. versicolor is known to prey upon P. pyralis by mimicking the flash patterns of P. pyralis, but we did not find an effect of light pollution on Photuris–Photinus predator–prey interactions. Our study suggests, that for some nocturnal insects, light-polluted areas may act as demographic traps, i.e., areas where immigration exceeds emigration and inhibition of courtship dialogues and mating reduces reproduction. Examining multiple factors affecting population growth in concert is needed to understand and mitigate impacts of light pollution on wildlife.     

Excitation energy transfer and chlorophyll orientation in the green alga Chlamydomonas reinhardi

We have investigated the process of intermolecular excitation energy transfer and the relative orientation of the chlorophyll molecules in the unicellular green alga Chlamydomonas reinhardi. The principal experiments involved in vivo measurements of the fluorescence polarization as a function of the exciting-light wavelength in the presence and in the absence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. We found that as the fluorescence lifetime increases upon the addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea that the degree of fluorescence polarization decreases over the excitation region from 600 to 660 nm. This result, we argue, implies that a Förster mechanism of excitation energy transfer is involved for Photosystem II chlorophyll molecules absorbing primarily below 660 nm. We must add that our results do not exclude the possibility of a delocalized transfer process from being involved as well. Fluorescence polarization measurements using chloroplast fragments are also discussed in terms of a Förster transfer mechanism. As the excitation wavelength approaches 670 nm the fluorescence polarization is nearly constant upon the addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea.Experiments performed using either vertically or horizontally polarized exciting light show that the fluorescence polarization increases as the exciting light wavelength increases from 650 to 673 nm. This suggests the possibility that chlorophyll molecules absorbing at longer wavelengths have a higher degree of relative order. Furthermore, these studies imply that chlorophyll molecules exist in discrete groups that are characterized by different absorption maxima and by different degrees of the fluorescence polarization. In view of these results we discuss different models for the Photosystem II antenna system and energy transfer between different groups of optically distinguishable chlorophyll molecules.     

Phytochrome-mediated phototropism in de-etiolated seedlings : occurrence and ecological significance

Phototropic responses to broadband far red (FR) radiation were investigated in fully de-etiolated seedlings of a long-hypocotyl mutant (lh) of cucumber (Cucumis sativus L.), which is deficient in phytochrome-B, and its near isogenic wild type (WT). Continuous unilateral FR light provided against a background of white light induced negative curvatures (i.e. bending away from the FR light source) in hypocotyls of WT seedlings. This response was fluence-rate dependent and was absent in the lh mutant, even at very high fluence rates of FR. The phototropic effect of FR light on WT seedlings was triggered in the hypocotyls and occurred over a range of fluence rates in which FR was very effective in promoting hypocotyl elongation. FR light had no effect on elongation of lh-mutant hypocotyls. Seedlings grown in the field showed negative phototropic responses to the proximity of neighboring plants that absorbed blue (B) and red light and back-reflected FR radiation. The bending response was significantly larger in WT than in lh seedlings. Responses of WT and lh seedlings to lateral B light were very similar; however, elimination of the lateral B light gradients created by the proximity of plant neighbors abolished the negative curvature only in the case of lh seedlings. More than 40% of the total hypocotyl curvature induced in WT seedlings by the presence of neighboring plants was present after equilibrating the fluence rates of B light received by opposite sides of the hypocotyl. These results suggest that: (a) phytochrome functions as a phototropic sensor in de-etiolated plants, and (b) in patchy canopy environments, young seedlings actively project new leaves into light gaps via stem bending responses elicited by the B-absorbing photoreceptor(s) and phytochrome.     

ON THE PLACE OF PHOTIC ADAPTATION

The progress of photic adaptation of Agriolimax, when studied by the method of compounding phototropic and geotropic vectors, is shown to be uninfluenced by the concurrent gravitational excitation. Direct proof is thus obtained that the adaptation to light, manifest in its steadily decreasing effectiveness as a stimulus during the course of exposure, is not due to any central nervous adjustment simulating "learning," but is due to photochemical changes in the receptors.     

WAVE LENGTH OF LIGHT AND PHOTIC INHIBITION OF STEREOTROPISM IN TENEBRIO LARV?

A definite intensity of white light is required (about 136 m.c.) to produce negative phototropic orientation of creeping Tenebrio larvæ away from contact with a vertical glass surface. This gives a measure of stereotropism in terms of phototropism, or reciprocally. The effectiveness of light for the suppression of stereotropism varies with wave length. It is therefore simple to obtain a measure of the relation between wave length and stimulating efficiency in this case of phototropic orientation. By determinations of the minimal energy required to inhibit stereotropism with different regions of the spectrum, it is found that the maximum effectiveness is sharply localized in the neighborhood of 535µµ. The curve connecting stimulating efficiency with wave length, while giving a picture of the effective absorption by the photosensory receptors, probably does not permit accurate characterization of the essential photosensitive material.