Ultrastructural Characteristics of the In Vitro Cell Cycle of the Protozoan Pathogen of Oysters, Perkinsus marinus

Ultrastructural characteristics of vegetative and zoosporangial stages of cultured Perkinsus marinus, a pathogen of the eastern oyster, Crassostrea virginica, were examined by transmission electron microscopy. An axenic cell culture was propagated from infected Chesapeake Bay oyster hemolymph. Different stages of the in vitro cell cycle, including schizonts and different size trophonts, were examined. Trophonts had spherical nuclei with wide perinuclear spaces, mitochondria with tubular cristae, and vacuoles with vacuoplasts. There were micropores on the inside of cell walls. A tubular network in the cytoplasm connected lomasomes to vacuoles, and contained vacuoplast precursor material. Vacuoplasts and precursor material diminished when cell cultures were not fed, suggesting a function in metabolite storage. Cells divided by schizogony or binary fission. Daughter cells in a schizont were not alike, and may specialize for different functions. Some of the daughter cells in a schizont died. Some hypnospores, directly isolated from infected oyster hemolymph enlarged in Ray's fluid thioglycollate medium, and were induced to zoosporulate. Zoosporangia contained varicose, hypha-like structures, whose apical tips gave rise to prezoospores. Ultrastructural characteristics of the vegetative and zoosporangial stages did not resemble any apicomplexan parasites other than members of the genus Perkinsus.     

The influence of morphological differences in bracken pinnules on the foliar uptake of aminotriazole

Bracken growing on an open hillside had greater development of both the upper and lower cuticular membranes than that growing under moderate shade. However, in the latter, aminotriazole uptake was less. This could be due to decreased spreading of the applied solution on the upper surface of shade-grown fronds and a decrease in stomatal and/or leaflet hair densities on the lower surface.     

Purification and some particle properties of anthriscus yellows virus, a phloem-limited semi-persistent aphid-borne virus

Anthriscus yellows virus (AYV), a phloem-limited virus transmitted in the semi-persistent manner by the aphid Cavariella aegopodii, was purified by treatment of leaf extracts with cellulasc, followed by differential and sucrose density gradient centrifugation. ‘The preparations contained isometric particles c. 29 nm in diameter which were unstable unless stored in buffer at pH 8.0 containing 1 mM CaCl₂,. The particles sedimented as two components, ’full‘ nucleoprotein particles with A₂₆₀/A₂₈₀= 1.83 containing about 42% nucleic acid, and ’empty‘ protein shells with A₂₆₀,/A₂₈₀= 0.73; their buoyant densities in CsCl solutions were 1.52 and 1.27 g/cm³. Respectively. Yields of ihe nircleoprotein particles were c. 1.75 mg/kg leaf tissue. The particles contained a single species of RNA, of mol. wt 3.6 × 10 “(10 000 nucleotides). Particle protein preparations contained four electrophoretic species, of mol. wt (× 10³) 35.0, 28.3, 23.3 and 22.3.C. aegopodii did not transmit AYV from purified preparations. A rabbit injected with AYV preparations produced antibodies that coated AYV particles in electron microscope tests, but gave variable reactions in immunosorbent electron microscopy (ISEM), depending on the composition of the medium. No reactions were obtained in enzyme-linked inimunosorbent asjay (ELISA). No serological relationship was detected in ISEM between AYV and any of 10 viruses that resembled it in one or more properties.     

Simulated global changes alter phosphorus demand in annual grassland

In the Jasper Ridge Global Change Experiment – an annual grassland with elevated carbon dioxide (CO₂), nitrate deposition, temperature, and precipitation – we used six indices of phosphorus (P) limitation to test the hypothesis that global changes that increase net primary production (NPP) increase P demand or limitation. All indices indicated that nitrate deposition, the only factor that stimulated NPP, increased P demand or limitation: (1) soil phosphatase activity increased by 14%; (2) P concentration in green and (3) senescent leaves of the dominant grass genus, Avena , dropped by 40% and 44%, respectively; (4) N : P ratios in green and (5) senescent Avena widened by 99% and 161%, respectively; and (6) total aboveground plant P decreased by 17% with elevated nitrate deposition. The other three factors, which did not stimulate NPP, did not increase P demand: based on two indices, enhanced precipitation decreased P demand (11% decrease in phosphatase activity, 19% increase in total aboveground P), and there was no evidence that elevated CO₂ or temperature altered P demand. In a meta-analysis to assess the generality of P constraints on growth increases from global change factors, we found that six of 11 N-limited ecosystems responded to N deposition with enhanced P limitation or demand, but did not detect significant effects of elevated CO₂ or warming.     

Effaced preservation in the Ediacara biota and its implications for the early macrofossil record

Abstract: Ediacaran structures known as ‘pizza discs’ or Ivesheadia have long been considered enigmatic. They are amongst the oldest known members of the Ediacara biota, apparently restricted to the Avalonian successions of Newfoundland and the UK, c. 579–560 Ma. Here, we suggest that these impressions are taphomorphs, resulting from the post‐mortem decay of the frondose Ediacaran biota. Ediacaran fossils range from well‐preserved, high‐fidelity variants to almost completely effaced specimens. The effaced specimens are inferred to have undergone modification of their original morphology by post‐mortem microbial decay on the sea floor, combined with sediment trapping and binding. In this style of preservation, morphological details within the organism became variously subdued as a function of the extent of organic decay prior to casting by overlying sediments. Decay and effacement were progressive in nature, producing a continuum of grades of preservation on Ediacaran bedding planes. Fossils preserved by such ‘effaced preservation’ are those that have suffered these processes to the extent that only their gross form can be determined. We suggest that the lack of detailed morphology in effaced specimens renders such fossils unsuitable for use as type material, as it is possible that several taxa may, upon degradation and burial, generate similar morphological taphomorphs. We here reinterpret the genus Ivesheadia as a taphomorph resulting from extensive post‐mortem decay of frondose organisms. Blackbrookia, Pseudovendia and Shepshedia from beds of comparable age in England are likewise regarded as taphomorphs broadly related to Charnia or Charniodiscus spp. To reflect the suggestion that such impressions are likely to be taphomorphs, and not taxonomically discrete, we propose the term ivesheadiomorphs to incorporate all such effaced taphonomic expressions of Ediacaran macrofossil taxa in Avalonian assemblages. Our recognition of effaced preservation has significant implications for Ediacaran taxonomy, and consequently for measures of Ediacaran diversity and disparity. It is implied that Avalonian assemblages preserve both organisms that were alive and organisms that were already dead at the time of burial. As such, the fossil assemblages cannot be taken to represent census populations of living organisms, as in prior interpretations.     

Intraspecific aggression, colony identity and foraging distances in Sudanese Microtermes spp. (Isoptera: Termitidae: Macrotermitinae)

Abstract. 1. Intraspecific aggression between termite major workers was used to obtain estimates of foraging distances for three Microtermes species in Sudan.
2. Maximum foraging distance recorded for M. sp. nr albopartitus (Sjöstedt) in Khartoum was 11.3 m, giving an estimated minimum colony area of 100 m². This is probably an underestimate. In the Tokar Delta, individuals from single colonies of M. najdensis Harris were encountered up to 42 m apart, giving a colony area of 1390 m².
3. Intraspecific aggression could not be used reliably to distinguish members of different colonies of M. lepidus Sjöstedt. Soil barrier formation between groups of workers in petri dishes may be of use as a supplementary technique, especially for species showing no clear aggression.
4. Experiments on isolated laboratory colonics of M. sp. Nr lepidus Sjöstedt, established from alates collected in Khartoum, further confirmed the value of inter-colony aggression for indicating colony identity.
5. The complications introduced into estimation of subterranean termite foraging areas by overlap and interdigitation of colonies are discussed.     

Prolonged Infusion of Fluids into Tree Seedlings Using Ascorbic Acid

A method was developed to infuse liquids into the stems of three-year-oldCercis canadensis L., Liriodendron tulipifera L., and Tiliacordata Mill. seedlings and to monitor the movement of fluidinto the stems. Ascorbic acid (14.2 mM) added to the infusionliquid, could increase the initial rate of fluid uptake 2- to3-fold compared with distilled water control treatments. Theascorbic acid treatment also prolonged fluid uptake about 4d longer than distilled water treatments. The effect of ascorbicacid on fluid uptake could not be correlated to the solutionpH, the antibiotic effect of high ascorbic acid concentrations,or to seedling height, trunk diameter or projected leaf area.Data did, however, suggest that the increased fluid uptake rateand the prolonged fluid uptake may be related to the anti-oxidantproperty of ascorbic acid. The accumulation of 1.0 g of ascorbicacid in 60 to 100 cm tall C. canadensis and L. tulipifera seedlingsdid induce defoliation and lateral bud break. The data presentedmay be useful in developing techniques for prolonged infusionof therapeutic compounds into trees and for studying, in vivo,wound response to xylem tissue. Key words: Ascorbic acid, liquid influsion, tree seedlings     

EFFECT OF QUESTION ORDER ON SENSORY PERCEPTION AND PREFERENCE IN CENTRAL LOCATION TRIALS

In the running of consumer studies aimed at obtaining information about products and services, it has become increasingly popular to include some sensory type questions about the characteristics of the test product as well as the standard question about overall preference. The implications of this for the resultant data are complex, and as Sudman and Schwarz (1989) point out question order effects have been implicated as one of the major causes of unreplicated or unexpected findings in survey research. This study aims to establish the effect of question order on overall preference scores and sensory scores in consumer studies. Results indicate that there is a significant effect of asking sensory questions on overall preference ratings and the position of the preference questions (relative to the sensory questions) also has implications for overall ratings of preference.     

Discontinuous ventilation and energetics of locomotion in the desert-dwelling female mutillid wasp, Dasymutilla gloriosa

Abstract. Data on the discontinuous ventilation cycle and cost of pedestrian locomotion in female Dasymutilla gloriosa (Sauss.), a desert-dwelling mutillid, are described and compared with equivalent data from other Hymenoptera. The discontinuous ventilation cycle was intermediate between that found in xeric and mesic hymenopterans, with the open phase being about 20% of the cycle. No noticeable flutter phase was observed. Thus D. gloriosa does not attempt to reduce respiratory water loss to the same extent as found in other desert dwelling Hymenoptera. The minimum cost of transport was significantly higher than that obtained for several ant species, indicating that ants are probably more efficient runners than any other Hymenoptera.     

Wavelength dependence of suppression of potato sprout growth by light

Abstract Light is used commercially to prevent the sprouts on seed potatoes from growing so long that they are knocked off at planting. We investigated the relationship between wavelength and growth inhibition, using a very long irradiation time of 23 d with a 12-h photoperiod. The inhibition showed a narrow peak of far-red activity centered on 707 nm, with a shoulder in the red whose size depended on the degree of inhibition chosen as standard, because the log photon-fluence rate/response lines were not parallel. There was also inhibitory activity in the blue (< 500 nm). In many respects the wavelength relationship resembled the action spectra for growth inhibition in dark-grown seedlings, but in the latter the red peak is, or quickly becomes, more pronounced than the far-red peak: this did not happen with potato sprouts. Blue light caused a positive phototropic response at similar or lower fluence rates. Greening became visible only at the highest fluence rates, between the two spectral regions inhibitory to growth. Broadband sources had much less inhibitory activity in the 650–750-nm region.