K. Vogt

Chemical identity of the chromophores of fly visual pigment

vanced that nickel inhibits either the synthesis of SMM or the transaminase of homocysteine or its precursors. Synthesis of cysteine [7] and hence homocysteine occurs in leaves. If vase solutions containing nickel ions inhibit the leaf synthesis of cysteine and homocysteine that explains why our leafy Chrysanthemum blooms responded to nickel by delayed flower senescence, whereas the leafless blooms of Papaver nudicaule did not. Our thanks are expressed to Dr. V.J. Bofinger of the Department of Mathematics for statistical advice. Received December 8, 1983

Sensitizing Pigment in the Fly

The sensitizing pigment hypothesis for the high UV sensitivity in fly photoreceptors (R1–6) is further substantiated by measurements of the polarisation sensitivity in the UV. The quantum yield of the energy transfer from sensitizing pigment to rhodopsin was estimated by electrophysiological measurements of the UV sensitivity and the rhabdomeric absorptance (at 490 nm) in individual receptor cells. The transfer efficiency is ≥ 0.75 in receptors with an absorptance in the rhabdomeres of 0.55–0.95. This result suggests that the sensitizing pigment is bound in some way to the rhodopsin. A ratio of two molecules of sensitizing pigment per one rhodopsin is proposed.

The compound eye of the tsetse fly (Glossina morsitans morsitans and Glossina palpalis palpalis)

Abstract We have examined the retina of the tsetse fly Glossina morsitans and G. palpalis using anatomical, optical, biochemical and electrophysiological techniques. The eye is basically very similar to those of other higher Diptera such as Musca and Calliphora. The ommatidial organization has an open rhabdom arrangement typical of a neural superposition eye. The central rhabdomeres R7 and R8 are smaller in diameter than peripheral rhabdomeres (R1-6) except at the dorsal margin of the eye, where they are greatly enlarged. The number of secondary pigment cells is unusually large with 16–18 surrounding each ommatidium. The facet lenses are also unusually thick with a weakly curved outer surface and a strongly convex inner surface. It is shown how this gives rise to the characteristic striped reflections from the tsetse eye by total internal reflection, and possible functions for this are considered. As in most other dipterans, the visual pigment chromophore is 3-hydroxy retinal and an ultraviolet sensitizing pigment, 3-hydroxy retinol is present also. Photoreceptor cells R1-6 have a similar spectral sensitivity to those in Musca, although the position of the green peak (500 nm) is some 10 nm longer. Two spectral classes of R7 correspond to the so-called 7y and 7p cells in Musca, with predominantly ultraviolet sensitivity, and the spectral sensitivity of the R8 cells encountered resembles that of so-called 8y cells (λ max 520 nm). Due to a dietary deficiency, the eyes of flies raised on porcine blood contain no traces of C40 carotenoids. This is correlated with the observation that the spectral sensitivity of both 7y and 8y cells are systematically higher in the blue (400–500 nm) than their counterparts in Musca or Calliphora.

Does retinol serve a sensitizing function in insect photoreceptors

Spectral sensitivity of the dorsal compound eye of Simuliid males (Nematocera) shows a maximum in the u.v. at 340 nm, and a shoulder or second, smaller maximum around 430 nm. The visual pigment--based on retinal and therefore a rhodopsin--has its absorption maximum at 430 nm. The 340 maximum is due to a sensitizing pigment that transfers energy to the visual pigment. The properties of the Simuliid-photoreceptor hence are similar to most of the photoreceptors in higher flies (Musca, Calliphora, Drosophila), that also have a u.v.-absorbing sensitizing pigment. The difference is that in Simuliids the sensitizing pigment is not 3-hydroxyretinol as in the higher flies but a different substance, most likely retinol.

Evidence for a sensitizing pigment in the ocellar photoreceptors of the fly (Musca, Calliphora)

SummaryA method is described that allows the spectral sensitivity of photoreceptors to be measured with high spectral resolution. It is shown that the sensitivity of the ocelli ofMusca andCalliphora has a vibrational fine structure in the ultraviolet, strongly indicative of a sensitizing pigment. The visual pigment has its absorption maximum close to 425 nm.

SPECTRAL EFFECTS OF THE PUPIL IN FLY PHOTORECEPTORS

SummaryPhotoreceptors of flies contain pigment granules which upon illumination of the receptors migrate towards the rhabdomere and act as a ‘longitudinal pupil’. Data in the literature concerning the effect of the pupil on the spectral sensitivity are contradictory. Therefore spectral sensitivity ofMusca photoreceptors upon light adaptation was reinvestigated.The change in spectral sensitivity of fly photoreceptors upon light adaptation as measured by Hardie (1979) was confirmed. Taking into account waveguide optics this change was explained from absorbance spectra of pupillary granules, measured by microspectrophotometry in squash preparations. Furthermore the pupil absorbance spectrum determined in vivo (Stavenga et al. 1973) was interpreted. The absence of a change in spectral sensitivity upon light adaptation measured by pupillary reflexion (Bernard and Stavenga 1979) is explained by a local-triggering of the pupil.

Optische Untersuchungen an der Cornea der MehlmotteEphestia kühniella

SummaryThe optical properties of fresh corneal lenses ofEphestia kühniella were investigated. The refractive index distribution in slices about 3 μm thick was measured with the interference microscope. An axial and radial variation was found, the radial distribution being symmetric to the lens axis. The lowest values (approx. 1.43) of the refractive index occur in the paraxial proximal region of the cone, while the highest values (approx. 1.54) are found at the distal boundary and the peripheral zone of the lens. This refractive index distribution is equivalent to that of a dispersive lens, whereas the convex corneal surface is a collecting lens of higher power.This result is confirmed by experiments with the intact lens. The proximal distance between cornea and focal plane is +37.5 μm (Image mediumn = 1.335). This value and the geometrical properties of the lens give an effective lens refractive index of 1.40; this is lower than any value found in the cornea slices. If the convex curvature of the lens is optically compensated, the lens forms virtual erect images of an object.Measurements of the central diffraction disc showed that the quality of imaging of the corneal lens is limited only by the lens aperture, and not by the refractive index distribution.ZusammenfassungDie optischen Eigenschaften unfixierter Cornealinsen vonEphestia kühniella wurden untersucht. Die Brechungsindexverteilung wurde interferenzmikroskopisch an ca. 3 μm dicken Schnitten gemessen. In der Cornealinse wurde eine kontinuierliche axiale und radiale Variation des Brechungsindex gefunden, die radiärsymmetrisch zur Linsenachse ist. Minima des Brechungsindex von ca. 1,43 liegen proximal im Achsenbereich der Linse, Maxima von ca. 1,54 an der distalen Linsenbegrenzung und im Randbereich. Diese Brechungsindexverteilung ist einer Zerstreuungslinse äquivalent, welche die sammelnde Wirkung der convexen Corneaoberfläche abschwächt.In Übereinstimmung mit diesem Befund stehen Experimente, die an der intakten Linse durchgeführt wurden. Die proximale Brennpunktschnittweite der plankonvexen Cornealinse beträgt +37,5 μm (Bildraum,n = 1,335). Daraus ergibt sich ein effektiver Brechungsindex der Linse von 1,40. Dieser ist niedriger als alle in Corneachnitten gemessenen Werte. Ist die konvexe Außenfläche der Linse optisch kompensiert, entwirft die Cornealinse aufrechte, virtuelle Bilder eines Objektes.Messungen der Größe des zentralen Beugungsscheibchens ergaben, daß die Abbildungsgüte der Cornealinse nur durch die Beugung am Linsenrand und nicht durch ihre Brechungsindexverteilung begrenzt ist.

The pigment system of the photoreceptor 7 yellow in the fly, a complex photoreceptor

SummaryThe 7y photoreceptor in the fly (Musca, Calliphora) retina harbours an unusually complex pigment system consisting of a bistable visual pigment (xanthopsin, X and metaxanthopsin, M), a blue-absorbing C40-carotenoid (zeaxanthin and/or lutein) and a uv sensitizing pigment (3-OH retinol).The difference spectrum and photoequilibrium spectrum in single 7y rhabdomeres were determined microspectrophotometrically (Fig. 2).The extinction spectrum of the C40-carotenoid has a pronounced vibrational structure, with peaks at 430, 450 and 480 nm (Fig. 3). The off-axis spectral sensitivity, determined electrophysiologically with 1 nm resolution shows no trace of this fine structure thus excluding the possibility that the C40-carotenoid is a second sensitizing pigment (Fig. 4).The absorption spectra of X and M are derived by fitting nomogram spectra (based on fly R1–6 xanthopsin) to the difference spectrum.λ max for X is 425 nm, and for M 510 nm (Fig. 5). It is shown that the photoequilibrium spectrum and the difference spectrum can be used to derive the relative photosensitivity spectra of X and M using the analytical method developed by Stavenga (1975). The result (Fig. 6) shows a pronounced uv sensitivity for both, X and M, indicating that the uv sensitizing pigment transfers energy to both X and M. A value of 0.7 forΦ, the relative efficiency of photoconversion for X and M, is obtained by fitting the analytically derived relative photosensitivity spectra to the absorption spectra at wavelengths beyond 420 nm.