A new mutant class of soybean lacks urease in leaves but not in leaf-derived callus or in roots

Summary We reported earlier the recovery of two classes of soybean urease mutants in soybean (Glycine max L. Merr. cv. Williams). Class I mutants lack the embryo-specific urease while class II mutants lack the activities of both urease isozymes, the embryo-specific and the ubiquitous urease, the latter found in all tissues examined. We report here the recovery of a true-breeding mutant, aj3, which represents the third phenotypic class: normal levels of embryo-specific urease and little or no ubiquitous urease. Unlike class II mutant plants which lack urease in all tissue, aj3 lacks urease activity only in leaves (ca. 2% normal activity); its roots have near normal urease activity. Callus derived from leaves of aj3 has 14% to 40% the urease activity of Williams 82 callus. This partial reduction in urease activity in aj3 callus is sufficient to reduce growth with urea as sole nitrogen source and to confer resistance to 50 mM urea added to callus maintenance medium. Leaves of aj3 produce more than 40 times the urease antigen expected from their urease activity. The aj3 trait is due to a single recessive lesion which is not allelic with lesions at theEu2, Eu3 (class II) orEu1 (class I) loci. We designate the aj3 genotype aseu4/eu4.     

The isolation and immunolocalization of iron-binding compounds produced by Gloeophyllum trabeum

Summary Low molecular weight iron-binding compounds are produced by the brown-rot fungus Gloeophyllum trabeum. These chelators may function in scavenging transition metals for fungal metabolism and extracellular enzyme production. Because of the low molecular mass of the chelate-metal complex (below 1000 Da), and the oxidizing potential of the bound transition metals, certain chelating compounds could also play a role in the early stages of cellulose depolymerization by brown-rot fungi. High-affinity iron-binding compounds were isolated and partially purified from both liquid cultures of the brown-rot Gloeophyllum trabeum and from infected wood. Chelating compounds purified by thin-layer chromatography were used to prepare specific antibodies. These antibodies were shown to detect the chelator in infected wood and liquid fungal cultures by enzyme-linked immunosorbent assay and could be used in immunotransmission electron microscopy to visualize the high-affinity iron-binding compounds in situ. Elucidating the physiological roles of fungal chelate-metal complexes and determining their function in lignocellulose depolymerization will help us to better understand the mechanism of wood biodegradation.Publication no. 1549 Maine Agricultural Experiment Station Offprint requests to: J. Jellison     

Observations of Barophilic Microbial Activity in Samples of Sediment and Intercepted Particulates from the Demerara Abyssal Plain

To better understand the ecological significance of pressure effects on bacteria in the abyssobenthic boundary layer, experimental suspensions of sediments and sinking particulates were prepared from samples collected in boxcore and bottom-moored sediment traps at two stations (depth, 4,470 and 4,850m) in the Demerara abyssal plain off the coast of Brazil. Replicate samples were incubated shipboard at 3°C and at both atmospheric and deep-sea pressures (440 or 480 atm [4.46 × 10⁴ or 4.86 × 10⁴ kPa]) following the addition of [¹⁴C]glutamic acid (<10 μg liter⁻¹) or yeast extract (0.025%) and the antibiotic nalidixic acid (0.002%). In seven of the eight samples supplemented with isotope, a barophilic microbial response was detected, i.e., substrate incorporation and respiration were greater under in situ pressure than at 1 atm (101.3 kPa). In the remaining sample, prepared from a sediment trap warmed to 24°C before recovery, pressure was observed to inhibit substrate utilization. Total bacterial counts by epifluorescence microscopy decreased with depth in each sediment core, as did utilization of glutamic acid. Significant percentages of the total bacterial populations in cold sediment trap samples (but not the prewarmed one or any boxcore sample) were abnormally enlarged and orange fluorescing after incubation with yeast extract and nalidixic acid under deep-sea conditions. Results indicated that in the deep sea, barophilic bacteria play a predominant role in the turnover of naturally low levels of glutamic acid, and the potential for intense microbial activity upon nutrient enrichment is more likely to occur in association with recently settled particulates, especially fecal pellets, than in buried sediments.     

Variation in chiasma frequency in male Trichosurus vulpecula (Marsupialia: Mammalia)

Chiasma frequency in spermatocytes was found to show extensive variation between individual males from a natural population of the marsupial Trichosurus vulpecula. Two factors which might contribute to the observed variation were investigated; season and age. However, neither of these had any significant effect on chiasma frequency or chiasma frequency variation.     

Targeted Selection Experiments and Enzyme Polymorphism: Negative Evidence for Octanoate Selection at the G6PD Locus in DROSOPHILA MELANOGASTER

Published studies have reported significant selection with respect to the G6pd locus for Drosophila melanogaster reared on Na-octanoate food. We have reexamined the selective effects of Na-octanoate on egg to adult viability with respect to the G6pd polymorphism using specially constructed X chromosomes. Four experiments were carried out using different 6Pgd backgrounds in two recombinant sets of chromosomes segregating for the G6pd locus but constructed so as to minimize variation over most of the X chromosome. In addition, two measures of viability were used, and the size of the experiments and their associated degrees of freedom are approximately double those reported in the former studies. Our results find no evidence for differential selection on G6pd genotypes (males and females) by Na-octanoate and, therefore, do not corroborate the positive results of selection reported by other investigators. The reasons for our different results are discussed.     

How do retroviral oncogenes induce transformation in avian erythroid cells?

The v-erb B oncogene, as well as other oncogenes of the src-gene family transform immature erythroid cells from chick bone marrow in vivo and in vitro. The erb B-transformed erythroid cells differ from normal late erythroid precursors (CFU-E) in that they have acquired the capacity to undergo self-renewal as well as to differentiate terminally. They also do not require the normal erythroid differentiation hormone, erythropoietin, for either process. Cooperation of v-erb B with a second oncogene, v-erb A, results in a differentiation arrest of the transformed cells, which now only use the self-renewal pathway. Studies with conditional and non-conditional mutants in both v-erb B and v-erb A will be presented to elucidate further how the transforming proteins encoded by these oncogenes, gp74erb B and gp75gag-erb A, affect the differentiation programme of the infected erythroid precursor with the outcome of hormone-independent leukaemic cells arrested at an early stage of erythroid differentiation.     

Genome structure of HBI, a variant of acute leukemia virus MC29 with unique oncogenic properties.

We have analyzed the viral RNA of a variant of avian acute leukemia virus MC29, termed HBI. This virus was isolated during in vitro passage of a partially transformation-defective (td) mutant of MC29 (td10H-MC29) in chicken macrophages. While td10H-MC29 has a reduced ability to transform macrophages in vitro or to induce tumors in vivo, HBI-MC29 transforms macrophages efficiently and induces in vivo a high incidence of lymphoid tumors. Electrophoretic analysis of HBI-MC29 genomic RNA revealed that it has a complexity of 5.7 kilobases, like the RNA of wild-type (wt) MC29, and that it is 0.6 kilobases longer than the 5.1-kilobase RNA of the deletion mutant td10H-MC29. Analysis of the viral RNAs of two clonal isolates of HBI-MC29 by T1 oligonucleotide fingerprinting showed that sequences from the viral transformation-specific region, v-myc, which are deleted in td10H RNA, are present in HBI RNA. Moreover, hybridization of HBI RNA to molecularly cloned subgenomic fragments of wtMC29 proviral DNA, followed by fingerprint analysis of hybridized RNA, showed that the entire v-myc-specific RNA sequences defined previously are present. Hybridization to cloned DNA of the normal chicken locus c-myc shows a close relationship between HBI v-myc RNA and c-myc DNA, especially in the sequences which were deleted from td10H-MC29. T1 oligonucleotide maps of HBI and td10H RNAs were prepared and compared. Total conservation of the oligonucleotide pattern is observed in the overlapping v-myc regions, while the partial structural genes gag and env show some variations, most of which can be directly proven to be due to point mutations or recombination with helper viral RNAs that were analyzed in parallel. Recombination of td10H-MC29 with c-myc, followed by recombinational and mutational changes in the structural genes during passage with helper virus, could be a possible explanation for the origin of HBI.