Linkage of Retinal to Opsin

RHODOPSIN, the visual pigment of vertebrate rods, has been shown to consist of a chromophore (11-cis retinal) bound to a protein (opsin)^1–2. It has been proposed that the linkage is a Schiff base between phosphatidyl ethanolaniine (PE) and retinal and that when exposed to light, the retinal migrates from PE to the ε-amino-group of a lysine residue in opsin^3–7. Most of the support for this theory comes from the observation that N-retinylidenephosphatidylethanolamine (N-RPE) can be extracted in the dark from rod outer segments (ROS)^3,4. Furthermore, N-retinylphosphatidylethanolamine (N-RH₂PE) has been extracted from ROS preparations after treating the visual pigment with acid and NaBH₄—conditions which are assumed fix retinal to its “native” binding site through a secondary amine linkage⁷. All these studies, however, were carried out on crude extracts of ROS in various detergents. These crude extracts contain large amounts of phospholipid and retinal which is not bound to opsin. Thus, the isolation of N-RPE from crude ROS extracts does not necessarily point to its involvement in the binding of retinal to opsin. In contradiction to these reports are findings that purified visual pigment contains no phospholipid^9,10 and that the molar concentration of N-RPE in bovine ROS is less than that of rhodopsin¹¹. We have taken advantage of the observation that visual pigment in the outer segment disks is continually being renewed¹² to label the rhodopsin with ³H-retinal and to show in yet another way that N-RPE does not exist in purified visual pigment.     

Action of Heparin on Platelet Electrophoretic Mobility

THE aggregating agents adenosine diphosphate (ADP) and noradrenaline induce a biphasic change in human platelet electrophoretic mobility¹. Small concentrations (0·005 mg ml.^?1 and 0·05 mg ml.^?1) increase platelet mobility after incubation for 10 min; high concentrations (0·05 mg/ml.) induce a decrease in mobility. The same change also occurs in pig² and rabbit³ platelet mobilities. Hampton and Mitchell⁴ showed that the addition of 1–50 U of heparin to plasma has no effect on the biphasic mobility of human platelets. Nevertheless, measurements of the electrophoretic mobility of pig platelets after intravenous infusion with heparin have led to in vitro studies of both pig and human platelets, which I shall now describe.     

The complementary effects of plant resistance and the choice of sowing and harvest times in reducing carrot fly (Psila rosae) damage to carrots

The benefits of combining a partially-resistant carrot cultivar with different sowing and lifting dates to reduce carrot fly, Psila rosae, damage were investigated at Wellesbourne in 1983 and 1984-85. The partially-resistant cv. Sytan was less damaged and supported fewer insects than the susceptible cv. Danvers on all lifting dates. The estimated reduction of carrot fly larvae on Sytan compared with Danvers ranged from 33 to 95%. Nine combinations of sowing and lifting dates provided more than 75% marketable roots of Sytan compared with only three combinations of dates for Danvers. An early June sowing of both cultivars provided roots of a marketable size with the least attack. More than 90% of Sytan roots were still marketable in December and fewer insects were produced by the end of the season on these roots than on those sown earlier. In addition, sowing in June decreased the number of pupae produced on cv. Danvers by 10 times compared with earlier sowings. Combining partial resistance with specific sowing and lifting times enabled satisfactory yields of marketable carrots to be obtained in a field infested by high populations of carrot fly.     

Preservation of baled hay with propionic and formic acids and a proprietary additive

Field-baled hay was incompletely preserved using propionic or formic acids. Results were most satisfactory, although moulding by Aspergillus glaucus group was still frequent, when die hay contained less than 30% water and propionic acid was used. However, much more propionic acid was needed than in laboratory experiments probably because poor distribution of acid in the bale, resulted in under-treated pockets of hay where moulds tolerant to propionic acid could grow and then spread to areas that would otherwise have been adequately treated. In Dewar flasks, moulds, particularly Paecilomyces varioti and the A. glaucus group, could spread from untreated hay into hay containing 2% w/w of propionic acid. Addition of 4 or 10% of propionic acid protected adjacent untreated hay from moulding. The concentration of propionic acid necessary to prevent flasks from heating and moulding increased with thickness of the untreated layers and with water content. Redistribution of acid in the bale after treatment was slow and much variation in acid levels occurred even between adjacent 1 cm segments of grass following storage. Spontaneous heating of moulding hay could cause migration of propionic acid in hay, assisting the spread of fungi. A proprietary additive did not prevent moulding at any hay water content tested.     

Changes in Carotenoid Composition of Certain Roses with Age

The carotenoid composition of the anthers and styles and thefruits of four roses of different ages have been investigated.ß-carotene and its epoxides were present at all stagesstudied, as were the ß-carotene derived xanthophyllauroxanthin and the -carotene derived flavoxanthin and chrysanthemaxanthin.As the various parts aged, the control of carotenoid synthesiswas removed, oxidative processes took place with the resultthat very few members of the -carotene series were found, andepoxy-carotenoids and their derivatives were the main carotenoidspresent. Rubixanthin, 3-hydroxy--carotene characteristic ofrose hips was found in fairly large amounts in anthers and stylesand -carotene was probably the precursor of this pigment. Rosehips were also investigated for their vitamin-A contents whichwere not as high as those of All Gold flowers.     

Monitoring populations of the carrot fly, Psila rosae, with sticky and water traps

The relative, effectiveness of Rebell®, small cylinder, large cylinder, windmill and water traps, the five types of trap used currently for monitoring populations of the carrot fly, Psila rosae, was assessed in nine field experiments, three in south west Lancashire, four in the Fens (Suffolk, Norfolk, Cambridgeshire), one in East Suffolk and one at Wellesbourne, Warwickshire. Regression analysis of the numbers of flies caught on each type of trap against the numbers caught on the Rebell® trap indicated that each trap samples a constant proportion of the fly population relative to the other traps. Therefore, provided the fly population was sufficiently large for insects to be caught on the least effective traps, any of the five traps would monitor adequately fluctuations in carrot fly populations. However, the Rebell® trap caught 4–17 times as many flies/trap and 5–7 times as many flieshnit area of trap as any of the other traps tested.
Operators considered the Rebell® trap to be the easiest to use. However, it was more expensive than any of the other traps tested.     

The allopatric phase of speciation: the sharp-beaked ground finch (Geospiza difficilis) on the Galápagos islands

Using microsatellite DNA variation, morphological measurements and sonagrams made from tape-recordings in the field, we examine die allopatric differentiation of six populations of the sharp-beaked ground finch, Geospiza difficilis , in the Galapagos archipelago. We ask how and why die populations became differentiated, and consider what die differences imply about speciation. An important factor is time; G. difficilis is one of the phylogenetically oldest species. Populations became differentiated by adapting in beak morphology to different food supplies. Since beak size and shape also function in conspecific mate recognition and choice, die potential for reproductive isolation from sister and parental taxa arose as a correlated effect of natural selection on resource-exploiting traits. This conforms to a standard explanation for the origin of pre-mating isolation as a byproduct of adaptive changes in allopatry without being adaptive itself. However, diis explanation is incomplete. Vocal characteristics also differentiated, partly as a result of natural and sexual selection independent of beak size change in environments with different sound transmitting properties. An additional element of chance is indicated by a comparison of closely-related populations on two islands, Wolf and Darwin, that are geographically close, and topographically and floristically similar. The populations have markedly different vocalizations. Morphological characters, vocalizations and genetic traits do not vary concordandy among die six populations. One population (Genovesa) is genetically more similar to other congeneric species. Phenotypic similarities with G. difficilis are the result of a uniquely long retention of shared ancestral traits. Arguments under the phylogenetic species concept justify recognizing this population as a separate species, Geospiza acutirostris. Under the biological species concept it should remain as currentiy classified, G. difficilis.     

Patterns of pupal mortality in field populations of Hydropsyche and Cheumatopsyche (Trichoptera: Hydropsychidae)

SUMMARY. 1. Up to 40% of hydropsychid pupal cases (from three stations on the Credit and Humber Rivers, Ontario, Canada) contained insects already dead when collected; chironomid infestation accounted for up to 82% of total mortality within a taxon from any one station. The remaining mortality appeared to be due to siltation.
2. For all taxa ( Cheumatopsyche Wallengren and four species of Hydropsyche Pictet), and at all stations, prepupae suffered significantly more chironomid-related mortality than did fully-developed pupae.
3. Chironomid infestation generally affected all species of Hydropsyche equally; at some stations, Cheumatopsyche pupae appeared to suffer less chironomid-related mortality than did co-existing Hydropsyche species.
4. Chironomid infestation affected a greater proportion of pupae at the station where the density of pupal cases (per sampling quadrat) was greatest.
5. Vertical distribution of the pupation site had no apparent influence on mortality attributed to either siltation or chironomid infestation.
6. Chironomid infestation varied seasonally; it was greatest in May and July-August at an upstream station, and peaked in June at the downstream stations.
7. Mortality attributed to siltation was relatively constant for all stages and taxa, at all stations, throughout the sampling programme.     

Ecology and colonial dynamics of some Pacific reef flat Didemnidae (Ascidiacea)

Non-cryptic didemnid ascidians containing the prokaryote Prochloron are abundant on the intertidal flat of many Pacific reefs. Species with sheet-like colonies (e.g. Diplosoma similis, Trididemnum paracyclops ) are characteristic of high wave energy situations and clean hard surfaces; didemnids in which the colony divides repeatedly into small cormomeres (e.g. Diplosoma virens, D. multipapillata, Lissoclinum voeltzkowi ) are in less exposed situations, often on algae or unstable substrata. The unusual back-reef cascade habitat of D. multipapillata on a Fijian fringing-reef is described. In Fiji, replicative division leads to population build-up between June and October, with a hot season decline in November-December. The effects of torrential rain in April 1980 are described. Studying L. voeltzkowi in permanent quadrats has shown that the populations of cormomeres are dynamic, with much movement occurring. The process of colony division is described in Diplosoma virms from the Great Barrier Reef. Possible advantages of didemnid dynamism discussed include maximization of periphery to area (perhaps increasing the efficiency of feeding and/or growth), the exclusion of competitors, and the mingling of clones to facilitate cross-fertilization.     

The Effects of Temperature on Leaf Growth in Cyperus longus, a Temperate C4 Species

Plants of the C₄ sedge Cyperus longus L. were grown at 10, 20and 30 °C. An asymptotic growth curve, the Richards function,was fitted to growth data for successive leaves. The mean rateof leaf appearance was a linear function of temperature with0.014 leaves appearing per day for every 1 °C increase intemperature. The instantaneous relative rate of leaf extensionshowed a marked ontogenetic drift which was most rapid at 30°C and slowest at 10 °C. The mean absolute extensionrate for foliage had a temperature coefficient of 0.16 cm d^–1° C^–1 in the range from 10 to 30 °C. The durationof leaf growth was independent of leaf number at 10 and 20 °Cbut increased linearly with leaf number at 30 °C. The smalldifferences in relative growth rate at the three temperaturesresulted in large differences in foliage area produced at theend of a 30 d growth period. The final foliage areas at 20 and10 °C were 51 and 9% respectively of that at 30 °C. Cyperus longus, temperature, leaf growth, Richards function, growth analysis