CHLOROPLAST DNA POLYMORPHISM AND PHYLOGENY IN THE B GENOME OF GLYCINE SUBGENUS GLYCINE (LEGUMINOSAE)

The B genome of Glycine subgenus Glycine comprises three diploid species whose monophyly is supported by morphological, crossing, and chloroplast DNA (cpDNA) data. Previous cpDNA studies indicated low levels of divergence among these taxa and failed to resolve cladistic relationships among them. More intensive studies of cpDNA variation were initiated, using additional restriction endonucleases and accessions. Results from cladistic analyses of over 50 restriction site characters indicate that there is considerable cpDNA polymorphism within this group of species, with a minimum of 27 plastome types occurring among the 74 accessions sampled. Levels of homoplasy observed in this group are relatively high (15%) for closely related congeneric species. There is only limited congruence between plastome type and taxonomic classification based on morphological characters. Explanations for this lack of concordance include: 1) the early state of taxonomic understanding in this group, 2) lack of resolution in the cpDNA tree caused by homoplasy and the small number of synapomorphic characters, 3) introgression among these interfertile, often sympatric taxa, and 4) maintenance of ancestral cpDNA polymorphisms resulting in shared plastomes among species.     

Identification of conditioned medium proteins from human cancer cells adapted to serum-free conditions

Recent studies have shown that human cancer cell lines can be adapted to grow in serum-free, unsupplemented RPMI-1640 (RO) medium. We have developed similar techniques to rapidly identify proteins of interest in serum-free conditioned medium (CM) of human lung cancer cell lines. Classic and variant small cell lung cancer (SCLC) lines were adapted to growth in RO medium. CM from each line was concentrated and fractionated on an anion-exchange column of a fast protein liquid chromatography system. Concentrates of each fraction were loaded onto lanes of minigels of an automated electrophoresis system. Analysis of the chromatograms reveals peaks seen only in CM of the classic SCLC lines. Electrophoretic analysis of the fractions containing these peaks reveal protein bands distinguishing between the subtypes of human SCLC. One protein was purified to homogeneity with subsequent reversed-phase chromatography and identified by protein microsequencing as histone H2B. These automated techniques have general use in the rapid identification of CM proteins associated with the differentiation or progression of the many types of neoplastic cells which can be adapted to growth in RO medium.     

Trypanosoma vivax: Courses of infection with three stabilates in inbred mouse strains

The courses of infection in inbred mouse strains were compared following infection with three Stabilates of high, intermediate, and low virulence of Trypanosoma vivax stock Zaria Y486. Mouse strains could only be shown to differ in their resistance to T. vivax infections as judged by the height of the initial parasitemia and survival times when a trypanosome population of low or intermediate virulence was used. A T. vivax population of high virulence was uniformly lethal. Comparison of lytic antibody titers between groups of resistant ($\text{C}\text{57}\text{B}\text{1}\text{6}$) and susceptible ($\text{Balb}\text{c}$) mice did not show any significant differences in titers of the surviving mice but the mice in either group which did not control the initial parasitemia had lower lytic antibody titers than those which did. A significantly larger number of $\text{Balb}\text{c}$ mice failed to control the initial infection as compared to the $\text{C}\text{57}\text{B}\text{1}\text{6}$. Treatment with cyclophosphamide did not ablate differences in susceptibility between the two strains. The use of congenic mice showed that these differences in susceptibility were not related to differences in the major histocompatibility complex between these strains.     

A simple enzyme assay for dry matter digestibility and its value in studying food selection by generalist herbivores

Summary The dry matter digestibility of 94 species of leaf was assayed by a simple method involving sequential treatment with pepsin and fungal cellulase enzymes. It was demonstrated that for foliage from rainforest trees of a wide range of dicotyledonous plant families the assay showed high positive correlation with estimates of dry matter digestibility obtained using rumenliquor from a fistulated steer. Both assays were found to reflect negative correlates of digestibility, notably fibre and condensed tannin, rather than the nutritional value of an item. The higher dry matter digestibility of immature leaves relative to mature leaves appeared to be accounted for by their lower fibre content. It is suggested that the pepsin/cellulase assay offers a cheap, quick, routine method of gaining information on the effects of some types of plant secondary compounds (digestibility reducers) on the food potential of different kinds of foliage to herbivores. Its use in studies of herbivory in rainforest areas in relation to analyses for plant secondary compounds and food selection by herbivores is discussed.Publication 20-018 of the Wisconsin Regional Primate Research Center     

Ontogeny of murine T lymphocytes: I. Maturation of thymocytes induced in vitro by tumor necrosis factor-positive serum (TNF+)

One question which is unresolved in developmental immunology is whether cortical thymocytes are the precursor cells which give rise to medullary thymocytes and peripheral T cells. Cortical thymocytes display a characteristic surface antigen phenotype (high TL and Thy-1, low H-2, no Qa-2, no Qa-3), are agglutinated by peanut agglutinin (PNA), and are unresponsive to concanavalin A (Con-A). The functionally more mature medullary thymocytes express a surface phenotype more closely resembling peripheral T cells (no TL, low Thy-1, high H-2, and some Qa-2), are not agglutinated by PNA, and are responsive to Con-A. An in vitro induction system has been devised in which mouse thymocytes undergo quantitative changes in surface antigens in less than 24 hr and increase their mitogen response to Con-A. The phenotypic changes are characterized by a decrease of TL and Thy-1 and an increase in H-2, Qa-2, and Qa-3. Studies in which thymocytes were fractionated on BSA gradients and by PNA agglutination demonstrate that the inducible cells have the properties of cortical thymocytes. Our data show that a subpopulation of cortical thymocytes can acquire phenotypic characteristics similar to medullary thymocytes and peripheral T cells.     

The allotetraploidization of maize

Summary Allotetraploidization is the creation of artifical allotetraploids from a normally diploid species. The possible value of allotetraploid maize has been discussed in Section I of this series. Allotetraploidization of maize can be achieved by restructuring a maize genome so that its chromosomes will not pair with those of the standard maize genome. This restructuring can be done by concentrating differential pairing affinity (DPA) factors into a single line by a recurrent selection type of breeding program. Because the divergence of the maize genome is a gradual process, it is necessary to devise a model for chromosome pairing and gene segregation in segmental allotetraploids. This has been done by considering pairing in each arm separately and then combining paired arms to form pairing configurations for whole chromosomes. The chromosome disjunction patterns are hypothesized and genetic ratios in relation to different levels of DPA are suggested.Contribution from the Science and Education Administration, U.S. Department of Agriculture, and the Agronomy Department, University of Missouri, Columbia, Missouri, Agricultural Experiment Station Journal Series No. 8090     

Peroxidase activity in mycelia of Aspergillus parasiticus that degrade aflatoxin

Summary Extracts of 9-day-old mycelia of Aspergillus parasiticus NRRL 2999 were assayed for peroxidase activity and for their ability to degrade aflatoxin. A positive relationship existed between rates of aflatoxin degradation and amount of peroxidase activity in these extracts. The supernatant fluid of homogenates from mycelia grown under similar conditions varied in amount of peroxidase present (170 to 2215 U/g). The fraction obtained, by precipitation with (NH₄)₂SO₄ at 45% of saturation, from six different homogenates prepared from three mycelial mats contained peroxidase and degraded aflatoxin. Rates of aflatoxin degradation by and amounts of peroxidase activity in each sample obtained from mycelial homogenates with (NH₄)₂SO₄ at 60% of saturation varied; however, when increased amounts of peroxidase activity were present, more aflatoxin was degraded and vice versa. Relatively little peroxidase activity was present in the fraction obtained with (NH₄)₂SO₄ at 30% of saturation and little or no aflatoxin was degraded by this precipitate. Trends for degradation of aflatoxin when more or less peroxidase activity was present in mycelial preparations suggest that the enzyme may be involved in degradation of aflatoxin by the Aspergillus.     

Development of secretagogue response in rat pancreatic acinar cells

Two to 3 days prior to birth, acinar cells of the rat pancreas acquire morphologic and biochemical characteristics of the adult gland. To determine if differentiation of the secretory apparatus coincides temporally with the capacity of the cell to respond to secretory stimuli, lobules of embryonic, neonatal, and adult rat pancreas were compared for their ability to respond to secretagogues presumed to act directly via hormone receptors [caerulein and carbamylcholine (carbachol)] or indirectly (cyclic nucleotide analogs and the Ca²⁺ ionophore A23187). Of all agents tested, only dibutyryl cAMP elicited discharge of secretory proteins at day 20 in utero and preceded hormone stimulation by 1 day. A23187 elicited discharge by Day 21 in utero; its action was near adult levels in contrast to hormonal stimuli whose effect was maximal only at birth. All secretagogues required Ca²⁺ and energy to induce discharge. Pulse-chase autoradiography of lobules from Day 20 embryonic glands indicated that the acinar cells were capable of transporting [³H]leucine-labeled proteins to zymogen granules at rates roughly equivalent to those in adult glands. SDS gel electrophoretograms confirmed that the bulk of ¹⁴C-amino acid incorporation into proteins at a given age was primarily into exportable proteins. The results indicate that acinar cells synthesize and package secretory proteins into zymogen granules about 2 days before they are capable of responding to hormonal stimuli and to intracellular effectors.     

Infrared spectroscopy of collagen and collagen-like polypeptides.

The set of synthetic polytripeptides and polyhexapeptides which can adopt a triple-helical form constitute a good model system for investigating collagen structure. Here we consider previous and new infrared spectroscopic studies on collagen and present the infrared spectra of a number of polymers with collagen-like features. The amide A band position for all triple-helical polypeptides is higher than that observed for most proteins and polypeptides, and this high frequency appears to be related to the degree of supercoiling of the triple helix. It is possible that with increased supercoiling of the three chains the angles between the groups involved in the intramolecular hydrogen bonds become less favorable, or these bonds may become unusually long. The frequency of the amide I band varies considerably for triple-helical polypeptides with different amino acid sequences, and often minor bands are observed. This finding contrasts with the observations for polypeptides in a pleated sheet or α-helical form, where the same amide I frequency is observed regardless of the amino acid composition. An explanation for this variation is proposed in terms of the hydrogen bonding properties of imino acids. Significant spectral changes in the amide I region are observed on hydration in the spectra of some triple-helical polypeptides, but corresponding changes have not been found in the collagens examined.