Spectral effects of the pupil in fly photoreceptors

Summary Photoreceptors 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.     

Contribution from coenzyme related molecules to evolution of photoreceptors

Coenzyme related substances, particularly flavins and pterins, were available from primordial chemical processes. When excited by near UV and short wave visible light, these compounds sensitise transfer of redox equivalents in homogenous solution and across membrane. Such reactions result in accumulation of free energy. The evolutionary age of some flavoproteins is close to the age of the Earth's biosphere. In modern organisms coenzyme related substances perform photosensor function for enzymes, such as DNA photolyase and nitrate reductase, and are chromophores for a photoreceptor regulating metabolism and development. Relevance of flavins and pterins both to prebiotic and current photobiological phenomena indicates their possible role in primitive photoreception.     

Electrophysiological measurement of the number of rhodopsin molecules in single Limulus photoreceptors

Two partly independent electrophysiological methods are described for measuring the number of rhodopsin molecules (R) in single ventral photoreceptors. Method 1 is based on measurements of the relative intensity required to elicit a quantal response and the relative intensity required to half-saturate the early receptor potential (ERP). Method 2 is based on measurements of the absolute intensity required to elicit a quantal response. Both methods give values of R approximately equal to 10(9). From these and other measurements, estimates are derived for the surface density of rhodopsin (8,000/micrometer2), the charge movement during the ERP per isomerized rhodopsin (20 X 10(-21) C), and the half-time for thermal isomerization of rhodopsin (36yr).     

Pigment migration and illumination of single photoreceptors in a moth

Summary The relation between intensity of illumination of single photoreceptors and position of the screening pigment was studied in the compound eye of the moth Deilephila elpenor. The amplitude of the response to test flashes of white light was measured in 7 dark adapted photoreceptor cells with the screening pigment in the extreme distal and in a proximal position. The experiments demonstrate that the response amplitude of individual photoreceptors varies with the pigment position. The associated variation in screening effect was 1.0 to 1.9 log units.The research reported in this study was supported by Swedish Medical Research Council, Sällskapet för Medicinsk Forskning and Stifteisen Gustaf och Tyra Svenssons Minne.     

Polarization and spectral sensitivity of single photoreceptors of the domestic cricket

The polarization and spectral sensitivity of single photoreceptors ofAcheta domesticus L. was measured. The morphological characteristics of the cricket rhabdome satisfy the conditions for a symmetrical model, for which the polarization sensitivity of a single photoreceptor is identically equal to the dichroism of a single microvillus. Characteristic curves of spectral sensitivity of all photoreceptors measured (24 cells) were similar and had two maxima: the principal at 500 nm and a secondary peak at 360 nm, characteristic of a pigment such as rhodopsin in the rods of the vertebrate retina. The mean value of polarization sensitivity measured was 2.28 ± 0.85 (mean ± standard deviation, 70 cells), suggesting the existence of slight preferential orientation of the dipole moments of the rhodopsin molecules along the axes of the microvilli.I. N. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Institute of Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 11, No. 5, pp. 483–490, September–October, 1979.     

Mechanisms regulating variability of the single photon responses of mammalian rod photoreceptors

Variability in the single photon responses of rod photoreceptors limits the accuracy with which the number and timing of photon absorptions are encoded. We investigated how much single photon responses of mammalian rods fluctuate and what mechanisms control these fluctuations. Mammalian rods, like those of toads, generated responses to single photons with trial-to-trial fluctuations 3-4 times smaller than other familiar signals produced by single molecules. We used the properties of the measured fluctuations to constrain models for how the single photon responses are regulated. Neither feedback control of rhodopsin's activity nor saturation within the transduction cascade were consistent with experiment. The measured responses, however, could be explained by multistep shutoff of rhodopsin or a combination of multistep shutoff and saturation.     

The degree of inhomogeneity of the absorbed cell nucleus doses in the bronchial region of the human respiratory tract

Radiation and Environmental Biophysics - Inhalation of short-lived radon progeny is an important cause of lung cancer. To characterize the absorbed doses in the bronchial region of the airways due...     

Changes in mimosa epicotyl soluble nucleic acid patterns: Comparisons between changes related to growth rate and changes related to degree of maturation

Soluble nucleic acids from Albizzia julibrissin epicotyl tissueswere extracted and fractionated at different times during lategermination. Seedlings were grown on two different growth regimes,one with a relatively constant growth rate and an increasingpercentage of mature tissues, and a second with an increasinggrowth rate but relatively constant percentage of mature tissues.Consistent changes were observed in distribution of specificsoluble nucleic acid fractions with growth rate and stage ofdevelopment. Stability of terminal groups of soluble nucleicacid also were related to growth and developmental patterns.Finally, degree of amino acid acceptance by total tRNA decreasedwith stage of development, but did not relate to growth ratesor percentage of mature tissues. ¹Contribution from the Missouri Agricultural Experiment Station.Journal Series No. 5586. (Received February 3, 1969; )     

Recognition and behaviour of caregiver managers related to oral care in the community

Objectives: The purposes of this study were to investigate the knowledge, practice and educational background of caregiver managers regarding oral health, how they cope with visiting activities, and to explore related factors to develop an appropriate working strategy for them in the community. Methods: The subjects were 102 caregiver managers, who voluntarily participated in a seminar organised by the M city government. The collected data were analysed to assess the relationship between the related factors of oral health, career and age, and the correlation amongst items of action process concerning oral health using Spearman’s correlation coefficient and Fisher’ s exact test with spss 14.0 for Windows. Results: The results were as follows; (i) the mean length of careers of home‐care staff and caregiver managers was 3.6 ± 3.2 and 1.6 ± 1.6 years respectively, (ii) 90.2% recognised the importance of oral care and 92.2% were interested in oral care, although 32.4% hesitated to provide oral care, (iii) the career of caregiver managers was not significantly related to recognition of concrete objectives of oral care, soft debris and symptoms of periodontal disease, but they recognised the effectiveness of oral care in prevention of aspiration pneumonia, (iv) there was a total of 11 significantly correlated items of knowledge, recognition and practice of oral care and (v) there was a total of 10 significantly correlated items amongst factors of action process. Conclusion: Results suggested that knowledge of oral care was related not only to the career but also to age and revealed a basic gap in the range of abilities between the respondent caregiver managers. Some did perform appropriate oral care and carried out the necessary processes.     

Tolerance to morphine-induced mydriasis in the rat pupil

Despite the commonly held view that tolerance does not develop to the pupillary effects of narcotics, recent studies have demonstrated tolerance to heroin-induced miosis in humans and to morphine-induced mydriasis in the mouse. Previous studies in this laboratory have shown that morphine produces a dose-related mydriasis and fluctuation (large amplitude, irregular oscillations in pupil diameter) in the rat pupil; the present study was designed to determine if tolerance develops to these effects following subcutaneous implantation of morphine pellets. We found that there is, indeed, tolerance to the morphine-induced mydriasis, but it is not complete. Furthermore, statistically significant tolerance does not develop to morphine-induced fluctuations in the rat pupil.     

From seed to seed: the role of photoreceptors in Arabidopsis development

As sessile organisms, plants have evolved a multitude of developmental responses to cope with the ever-changing environmental conditions that challenge the plant throughout its life cycle. Of the many environmental cues that regulate plant development, light is probably the most important. From determining the developmental pattern of the emerging seedling, to influencing the organization of organelles to best maximize energy available for photosynthesis, light has dramatic effects on development during all stages of plant life. In plants, three classes of photoreceptors that mediate light perception have been characterized at the molecular level. The phytochromes recognize light in the red portion of the spectrum, while cryptochromes and phototropins perceive blue and UVA light. In this review, we discuss the different aspects of development that are regulated by these photoreceptors in the model plant species Arabidopsis thaliana and how the phytochromes, cryptochromes, and phototropins bring about changes in development seen in the growing plant.     

Solvent-dependent conformational behaviour of lipochitoligosaccharides related to Nod factors.

The solution conformation of two lipooligosaccharides related to Nod factors or lipochitoligosaccharides have been analysed by 1D and 2D 1H and 13C NMR spectroscopy, molecular mechanics and dynamics calculations. The obtained data indicate that the glycosidic torsion angles have restricted fluctuations, but may adopt a variety of shapes. Remarkably, the relative orientation of the fatty acid chain towards the oligosaccharide backbone is solvent dependent. In water solution, the acyl residue and the oligosaccharide adopt a quasi-parallel orientation for a significant amount of time.     

Factors related to aggressive nest protection behaviour: a comparative study of Holarctic Waders

Data on 12 factors presumed to influence the distribution of aggressive nest defence in 111 species of waders (incubation-sharing by the parents, number of parents present near the nest, incubation time, nest habitat, breeding latitude, body mass, wing loading, wing structure, detectability on the nest, predator regime, coloniality and alternative prey) were collected from literature and field researchers. Body mass and number of parents present on the nest territory (within response range when avian predators appear) explain 50% of the variation in aggressive defence behaviour. The results support the notion that ecological conditions like predation pressure are important in shaping wader parental care systems, with implications for mating systems. Altogether, the investigated factors explain around 70% of the variation in the samples. Future research on the level of individuals is suggested in order to explain the remaining variation.