TheRhizobium-legume symbiosis Two methods to discriminate between nodules and other root-derived structures

Summary Two methods have been developed in order to discriminate between lateral roots, nodules and root-derived structures which exhibit both root and nodule histological features and which can develop on legumes inoculated with certainRhizobium mutants. The first method, known as the clearing method, allows the observation by light microscopy of cleared undissected root-structures. The second, known as the slicing method, is a complementary technique which provides a greater degree of structural information concerning such structures. The two methods have proved invaluable in defining unequivocally the nature of the interaction between a rhizobial strain and a legume host.     

A murine model for the study of the impact ofAspergillus fumigatus inoculation on the foeto-placental unit

The mycotoxin cyclopiazonic acid (CPA) is a potential contaminant of processed foods, grain and poultry. Twelve male Sprague-Dawley rats were given oral doses of 0, 0.2, 0.6, 2.0 or 4.0 mg CPA/kg body weight/day for 13 consecutive weeks to study its potential subchronic toxicity. No dose-related mortality or morbidity occurred. General appearance, behavior, body weight gain and food consumption of all groups were similar. CPA had no definite adverse hematologic or serum chemistry effects, although serum creatinine concentrations of rats given 2.0 and 4.0 mg CPA/kg BW were increased after seven and 13 weeks. Mild to focally moderate acute inflammation of the lamina propria and submucosa of the gastric epithelium was found in animals given 0.6 mg CPA/kg BW. No other dose-related microscopic lesions were found. Ultrastructural examination of the livers revealed subtle disruption of the cisternal pattern of the endoplasmic reticulum with ribosomal detachment in animals receiving 4.0, but not 2.0, mg CPA/kg BW. These data suggest that the toxic effects in rats of repeated, daily oral exposure to CPA may be less than previously reported. The possible relationship between toxicity and CPA epimerization is considered.     

Synthesis and physicochemical properties of oligonucleotides built with either alpha-L or beta-L nucleotides units and covalently linked to an acridine derivative.

Modified deoxynucleosides 2'-deoxy-beta-L-uridine, beta-L-thymidine, alpha-L-thymidine, 2'-deoxy-beta-L-adenosine and 2'-deoxy-alpha-L-adenosine were synthesized and assembled as homooligomers, respectively: octa-beta-L-deoxyuridylates, octa beta-L and alpha-L-thymidylates and tetra beta-L and alpha-L-deoxyadenylates. These unnatural oligomers were then substituted with an acridine derivative. The binding studies of these modified oligonucleotides with D-ribo- and D-deoxyribopolynucleotides were carried out by absorption spectroscopy. While beta-L-d(Up)8m5Acr, beta-L-(Tp)8m5Acr, alpha-L-(Tp)8m5Acr did not interact with poly(rA) and poly(dA), beta-L-d(Ap)4m5Acr and alpha-L-d(Ap)4m5Acr did form double and triple helices with poly(rU) and poly(dT), respectively. Their stability towards nuclease digestion was studied through comparison with that of octa-beta-D-thymidylate and tetra beta-D-deoxyadenylate covalently linked to an acridine derivative. One endonuclease (nuclease P1 from Penicillium citrinum) and two exonucleases (a 3'-exonuclease from Crotalus durissus venom and a 5'-exonuclease extracted from calf thymus) were employed. beta-L- and alpha-L-oligomers demonstrate a high resistance toward nuclease digestion.     

Male-like behaviour in an all-female lizard: relationship to ovarian cycle

A quantitative analysis of the relationship between pseudocopulatory behaviour and the ovarian cycle in the parthenogenetic lizard Cnemidophorus uniparens indicates (1) that this behaviour is frequently and regularly expressed by captive individuals, and (2) that the sexual role, either male-like or female-like, exhibited by an animal is correlated with its ovarian state. The expression of female-like behaviour patterns was associated with and primarily limited to the vitellogenic stage of the cycle. Male-like behaviour patterns occurred most frequently during post-ovulatory stages but was not limited to these stages. Neither behavioural role was ever expressed by non-reproductive individuals. Reproductive individuals often alternated in assuming the female-like and male-like roles during the progress of the ovarian cycle. These observations suggest that pseudosexual behaviour is hormonally activated in this species. However, it also appears that the prevailing social situation is an important factor determining which behavioural role is taken. This work strengthens the hypothesis that pseudosexual behaviour in all-female lizards occurs as the result of natural selection.     

Biosynthesis and distribution of ecdysone and 20-OH-ecdysone in Aedes aegypti

The distribution and biosynthesis of ecdysone and 20-hydroxyecdysone (20-OH-ecdysone) was followed in sugar- and blood-fed female Aedes aegypti. In both sugar- and early blood-fed animals most of the ecdysteroid determined by radioimmunoassay was found outside the ovary. Twenty-four to 40 h after blood feeding, however, ecdysteroid was distributed between ovary and carcass in the ratio of 1:1.5. Ecdysteroid titer reached a plateau between 18 to 40 h after the blood meal and decreased thereafter. Analysis of the ecdysteroid titer using thin layer chromatography (TLC) and high performance liquid chromatography (HPLC) revealed that both 20-OH-ecdysone and ecdysone were synthesized after the blood meal. The ratio of 20-OH-ecdysone to ecdysone remained essentially constant and fluctuated in parallel throughout egg development. Chromatography of the early ecdysteroid peak (8 h after feeding) using TLC and HPLC indicated that although it cross-reacted with ecdysteroid antibodies, it did not have the same elution times as ecdysone and 20-OH-ecdysone and is, therefore, probably a precursor of these ecdysteroids. Injections of egg development neurosecretory hormone (EDNH) preparation purified to near homogeneity, into ligated abdomens, induced ecdysteroid synthesis only if the abdomens were first treated with methoprene (12.5 pg). Methoprene at this concentration did not stimulate ecdysteroid synthesis in these abdomens. When blood-fed females were treated with [4-¹⁴C] cholesterol and analyzed using TLC and HPLC procedures, both [¹⁴C]labeled ecdysone and [¹⁴C]labeled 20-OH-ecdysone were synthesized in the ratio of 1:1.5. This report is the first to show that both ecdysone and 20-OH-ecdysone are synthesized in vivo in female A. aegypti.     

Induction of pregnancy-associated murine protein-1 in dwarf mice by human growth hormone

Pregnancy-associated murine protein-1 (PAMP-1) could not be detected in peripheral blood of female dwarf mice (genotype dw/dw of the DW strain). By contrast the normal size females of the DW strain (genotypes +/+ and +/dw) had PAMP-1 serum levels of 18.9 AU +/- 15.7 AU/ml. Following administration of biosynthetic human growth hormone (hGH) every 2 h for 52 h PAMP-1 was detected in all dwarf females at concentrations of 16.0 AU +/- 3.3 AU/ml. The albumin levels in the circulation of DW females of normal size were significantly higher (P less than 0.05) than those of DW dwarfs, and the hGH administration did not change the serum albumin levels. The present experiment adds weight to the suggestion that the PAMP-1 serum level is regulated by GH.     

Isolation of a pathogenic clone of mouse mammary tumor virus.

Exogenous mouse mammary tumor virus (MMTV) was cloned from a GR mammary tumor. Clone lambda GRT39 contained a full-length integrated MMTV(GR) provirus and both 5' and 3' host flanking DNA. The lambda GRT39 provirus had no apparent structural changes associated with cloning and retained the exogenous MMTV gag gene poison sequence. When introduced into rat mammary adenocarcinoma LA7 cells, the lambda GRT39 provirus was fully expressed. lambda GRT39-transfected LA7 cells made MMTV RNA, had gp52 SU protein on the cell surface, and produced B-type retrovirus particles characteristic of MMTV. Mammary tumors developed in hormone-stimulated BALB/c females injected with MMTV from lambda GRT39-transfected LA7 cells [MMTV (lambda GRT39)]. The tumors had new, clonally integrated copies of the MMTV(lambda GRT39) provirus and were expressing MMTV antigen. These data indicate that the lambda GRT39 provirus is biologically active and pathogenic.     

Abortion of infection during the Rhizobium meliloti—alfalfa symbiotic interaction is accompanied by a hypersensitive reaction

Nodulation, the organogenetic process resulting from the symbiotic interaction between Rhizobium and legumes, is under the feedback control of the plant. However, the autoregulatory mechanisms controlling root nodule formation are poorly understood. In this paper it is shown that alfalfa can react to infection by its symbiont Rhizobium meliloti by eliciting a defence mechanism similar to the hypersensitive reaction (HR) observed in incompatible plant-pathogen interactions. After the first nodule primordia have been induced, an increasing proportion of infection threads abort in a single or a few root cortical cells in which both symbionts simultaneously undergo necrosis. Autofluorescent, cytochemical and immunolocalization assays revealed that phenolic compounds and proteins associated with defence mechanisms in plants have accumulated in the necrotic cells. These results lead to the proposition that the elicitation of a HR is part of the mechanism by which the plant controls infection and, therefore, regulates nodulation.     

Conservation evaluation of nine Hong Kong mangals

A comparative analysis of the conservation value of nine Hong Kong mangals spread across Hong Kong has been undertaken. The analysis is based on both biological and socio-economic attributes. Biological attributes used in the analysis include plant species richness, benthic and arboreal gastropod species richness, occurrence of rare species within each site, and site representativeness. A review of the past and present development and development plans around and within each site has been undertaken to assess the comparative degree of hazard to each mangal. The drastic decline of mangal habitats throughout Hong Kong highlights the need for conservation of what remains today. Priorities and strategies for conservation of these nine mangals are discussed with particular emphasis on the preservation of biodiversity and the management of these habitats as education and research sites.Department of Applied Biology & Chemical Technology, Hong Kong Polytechnic