Characterisation of an Australian isolate of tomato yellow top virus

An Australian isolate of tomato yellow top virus (TYTV-A) was transmitted in the persistent manner by the aphid Myzus persicae. Its host range was mainly restricted to the Solanaceae, though Capsella bursa-pastoris and Gomphrena globosa were symptomlessly infected. TYTV-A was purified from Physalis Joridana, using an enzyme-assisted method in which the initial tissue homogenate was incubated with cellulase. Yields of purified virus were 100–900 μg/kg tissue and depended on the age of the infected plants. Maximum yields were obtained 4–5 wk after inoculation. The particles of TYTV-A were c. 24 nm in diameter, had a buoyant density of 1.34 in caesium sulphate and a coat protein mol. wt of c. 25.7 × 10³. TYTV-A was shown to be closely related serologically to potato leafroll virus (PLRV), TYTV from New Zealand and more distantly related to several other luteoviruses. An antiserum to TYTV-A was used in enzyme-linked immunosorbent assay tests to detect TYTV in field-infected tomato plants and also luteoviruses from potato plants with leafroll symptoms. It is clear that TYTV-A is a luteovirus closely related to PLRV.     

Acanthamoeba stevensoni N. Sp. (Protozoa: Amoebida) from Sewage-Contaminated Shellfish Beds in Raritan Bay, New York

Marine sediments from 12 shallow water stations in Raritan Bay, New York were tested for the presence of Acanthamoeba. Eight stations were positive for one or more species of Acanthamoeba, A. castellanii, A. comandoni, A. hatchetti, A. lenticulata, A. polyphaga, A. rhysodes, and Acanthamoeba spp. Isolates that grew at 38–40° C were found at four stations (A. comandoni, A. lenticulata, and two unidentified strains). The two unknown strains were characterized on the basis of morphological features, isoenzyme profiles, and mouse pathogenicity tests. One of the two strains was determined to be a new species and is designated herein as Acanthamoeba stevensoni n. sp., ATCC 50388. Mature cysts were most similar to those of morphological Group II of Pussard & Pons (1977). Acanthamoeba stevensoni n. sp. was isolated from inshore coastal sediments where seawater ranged from 20–30%‰ (ppt.). The sediments supported commercially valuable populations of hard clams, Mercenaria mercenaria, that required depuration prior to sale because of contamination by sewage-associated bacteria.     

Genes Encoding Antigenic Surface Glycoproteins in Pneumocystis from Humans

Pneumocystis is a eukaryotic microbe that causes pneumocystosis, an AIDS-associated pneumonia. Pneumocystosis also occurs in many other mammalian species, and animal-derived organisms have been extensively utilized in Pneumocystis research. Pneumocystis from diverse hosts contain a large glycoprotein (gpA/MSG) on the surface. Antibodies elicited against gpA/MSG of Pneumocystis from humans sometimes cross-react with epitopes on proteins of similar size from Pneumocystis from other host species. Here we report the isolation and partial sequence of two presumptive gpA/MSG genes from human-derived Pneumocystis. The cloned human-derived Pneumocystis gpA/MSG genes and predicted peptides were different from those previously isolated from Pneumocystis from rats and ferrets. The genome of human-derived Pneumocystis contained multiple copies of sequences related to the two cloned gpA/MSG genes.     

Molecular Mechanisms of Signal Integration in Hypothalamic Neurons

SYNOPSIS. The purpose of this paper is to describe our studiesfocused on the mechanisms by which hypothalamic neurons processmultiple signals and produce an integrated response. We illustrateour research strategy by reviewing our work on two separateneural systems: the hypothalamic paraventricular nucleus (PVN)and the suprachiasmatic nucleus (SCN). We have focused on differentpeptidergic subpopulations within these nuclei to address twoissues. In the PVN, we concentrate on thepopulation of neuronscontaining thyrotropin-releasing hormone (TRH). These neuronsare inhibited by thyroid hormones, but activated by cold exposure.Using a molecular approach, we have demonstrated that theseconflictingsignals simultaneously act on the same population of TRH neurons.This system will continue to be a productive model to studythe mechanisms by which neurons process multiple signals. Inthe SCN, we concentrate on the population of neurons containingvasoactive intestinal peptide (VIP), peptide histidine isoleucine(PHI) and gastrin releasingpeptide (GRP). We have demonstratedthat injection of all three peptides into the SCN of hamstersmimics the phase-delaying effects of light on circadian wheelrunning behavior. In addition, the genes encoding these peptidesexhibit different 24-hour profiles of changes in neurons ofthe SCN. These data support the hypothesis that one mechanismby which these neurons produce an integrated response is bychanging the concentration ratio of co-released peptides.     

Growth and maintenance components of leaf respiration of cotton grown in elevated carbon dioxide partial pressure

Elevated atmospheric carbon dioxide partial pressures have been shown to have variable direct and indirect effects on plant respiration rates. In this study, growth, leaf respiration, and leaf nitrogen and carbohydrate partitioning were measured in Gossypium hirsutum L. grown in 35 and 65 Pa CO₂ for 30d. Growth and maintenance coefficients of leaf respiration were estimated using gas exchange techniques both at night and during the day. Elevated CO₂ stimulated biomass production (107%) and net photo-synthetic rates (35–50%). Total day-time respiration (R_d) was not significantly affected by growth CO₂ partial pressure. However, night respiration (R_n) of leaves grown in 65 Pa CO₂ was significantly greater than that of plants grown in 35 Pa CO₂. Correlation of R_d and R_n with leaf expansion rates indicated that plants in both CO₂ treatments had equivalent growth respiration coefficients but maintenance respiration was significantly greater in elevated CO₂. Increased maintenance coefficients in elevated CO₂ appeared to be related to increased starch accumulation rather than to changes in leaf nitrogen.     

Ecology of body size in Drosophila buzzatii: untangling the effects of temperature and nutrition

Abstract.

• 1 A method of separating the effects of two important determinants of body size in natural populations, temperature of larval development and level of larval nutrition, by making measurements of thorax length and wing length of adult flies is investigated.
• 2 I show that at any given time variation in body size of Drosophila buzzatii from two sites in eastern Australia is determined primarily by variation in the quality of nutrition available to larvae.
• 3 Throughout the year adult flies are consistently at least 25% smaller in volume than predicted for optimal nutrition at their predicted temperature of larval development.
• 4 Nutritional stress is therefore a year-round problem for these flies.
• 5 Measurements of adult flies emerging from individual breeding substrates (rotting cactus cladodes) show that there is substantial variation among these substrates in the nutrition available to larvae.
• 6 This method will allow study of spatial and temporal variation in the temperature of larval substrates and in the nutritional resources available to flies in natural populations.

     

Evaluation of selected cowpea varieties for resistance to Aphis craccivora Koch (Homoptera: Aphididae) at the seedling and podding phase

Twelve varieties of cowpea (Vigna unguiculata) were tested at the seedling and podding growth phases for resistance to infestation and damage to Aphis craccivora Koch. Nine of these cowpeas have previously been known to exhibit seedling resistance and the other three, susceptibility to the insect. A. craccivora could not colonise pods of TVu 9930. Pods of Tvu 36 also manifested a high level of resistance to the aphid. The three seedling susceptible varieties proved quite susceptible to A. craccivora at the podding phase. The other varieties were more resistant to the aphid in the seedling phase than in the podding phase.