The influence of pre- and post-zygotic barriers on interspecific Corymbia hybridization

Background and Aims

Corymbia species from different sections hybridize readily, with some of increasing economic importance to plantation forestry. This study explores the locations of reproductive barriers between interspecific Corymbia hybrids and investigates the reproductive success of a wide taxonomic range of C. torelliana hybrid crosses.

Methods

Pollen, pistil and embryo development were investigated for four C. torelliana crosses (×C. torelliana, ×C. citriodora subsp. citriodora, ×C. tessellaris and ×C. intermedia) using fluorescent and standard microscopy to identify the locations of interspecific reproductive isolating barriers. Corymbia torelliana was also crossed with 16 taxa, representing six of the seven Corymbia sections, both Corymbia subgenera and one species each from the related genera, Angophora and Eucalyptus. All crosses were assessed for capsule and seed yields.

Key Results

Interspecific C. torelliana hybridization was controlled by pre-zygotic reproductive isolating barriers inhibiting pollen adhesion to the stigma, pollen germination, pollen tube growth in the style and pollen tube penetration of the micropyle. Corymbia torelliana (subgenus Blakella, sect. Torellianae) was successfully hybridized with Corymbia species from subgenus Blakella, particularly C. citriodora subsp. citriodora, C. citriodora subsp. variegata, C. henryi (sect. Maculatae) and C. tessellaris (sect. Abbreviatae), and subgenus Corymbia, particularly C. clarksoniana and C. erythrophloia (sect. Septentrionales). Attempted intergeneric hybrids between C. torelliana and either Angophora floribunda or Eucalyptus pellita were unsuccessful.

Conclusions

Corymbia hybrids were formed between species from different sections and subgenera, but not with species from the related genera Angophora or Eucalyptus. Reproductive isolation between the interspecific Corymbia hybrid crosses was controlled by early- and late-acting pre-zygotic isolating barriers, with reproductive success generally decreasing with increasing taxonomic distance between parent species. These findings support the monophyly of Corymbia and the close relationships of infrageneric clades. The hybridizing propensity of Corymbia species provides opportunities for breeding but suggests risks of environmental gene flow.     

Molecular docking analysis of stevioside with Akt and PPARγ

Stevioside is a diterpenoid glycoside consisting of an aglycone (steviol) and three glucose molecules. It is commonly used as an anti-hyperglycemic food because of its non-caloric property. Therefore, it is of interest to document the interactions of stevioside with AKT & PPAR-γ proteins using Autodock Vina PyRx docking techniques. Results of the docking studies indicate that stevioside had more than two hydrogen bond interactions with the AKT and PPAR γ protein for further consideration.     

Classification of the insulin-like growth factor binding proteins into three distinct categories according to their binding specificities

Competitive binding experiments with insulin-like growth factor (IGF)-1, IGF-2 and des-(1-3)-IGF-1 have confirmed the interpretation based on limited amino-terminal sequence analysis that at least three types of IGF binding protein occur. In addition to the acid stable subunit of the large serum binding protein which exhibits des-(1-3)-IGF-1 binding only slightly less than IGF-1, the small IGF binding proteins can be separated into two classes based on differences in des-(1-3)-IGF-1 and IGF-2 binding potencies.     

Characterization of WiDr: A human colon carcinoma cell line

Summary We describe the establishment and characterization of WiDr, a cell line derived from a human colon carcinoma. It produces carcinoembryonic antigen in culture, and has a doubling time of 15 hr with plating efficiency of 51%. The HLA antigenic profile and the allozyme genetic signature (composed of eight gene-enzyme systems) of WiDr cells are different from those of HeLa cells. Furthermore, WiDr cells possess three marker chromosomes, again distinct from the HeLa marker chromosomes. Finally, it is highly tumorigenic in four different xenogeneic animal models. Based on these studies, WiDr represents a useful model cell line for tumor cell biology investigations.     

Effects of clipping and soil compaction on growth,morphology and mycorrhizal colonization of Schizachyrium scoparium,a C4 bunchgrass

Summary A factorial design of clipping and compaction was used to study the responses of Schizachyrium scoparium and its mycorrhizal symbionts to these stresses. All treatment combinations significantly reduced the growth and biomass of plants relative to controls. Compaction significantly reduced tillering and crown expansion while clipping increased tillering early in the growing season and reduced it later. Mycorrhizal colonization of roots was highest in the clipped plots and lowest in compacted plots. Spore number was highest in compacted plots and lowest in clipped plots. It appears that spore number may be negatively correlated with root growth since any treatment that reduced plant growth yielded higher spore numbers. The combination of clipping and compaction reduced plant growth the most, but had intermediate effects on mycorrhizal colonization and spore number.     

Effective use of regional intensive therapy units.

OBJECTIVE--To determine the effectiveness of regional intensive therapy units. DESIGN--Retrospective and prospective study of patients transferred to a regional intensive therapy unit over four years. SETTING--Glasgow regional intensive therapy unit. MAIN OUTCOME MEASURES--Severity of illness was assessed at the time of referral to the unit with the acute physiological and chronic health evaluation (APACHE) scoring system. Mortality was calculated. RESULTS--A significant association was found between increasing duration of illness before transfer and mortality, which was independent of the severity of illness. Mortality also varied depending on the referring hospital. CONCLUSIONS--When transfer of critically ill patients is required this should be done as early as possible to make best use of the services available. The mortality of patients transferred after 10 days casts doubt on whether further aggressive intensive therapy is appropriate.     

Cloning, sequence analysis, and expression of genes encoding xylan-degrading enzymes from the thermophile "Caldocellum saccharolyticum"

A lambda recombinant bacteriophage coding for xylanase and beta-xylosidase activity has been isolated from a genomic library of the extremely thermophilic anaerobe "Caldocellum saccharolyticum." Partial Sau3AI fragments of the lambda recombinant DNA were ligated into pBR322. A recombinant plasmid with an insertion of ca. 7 kilobases of thermophilic DNA expressing both enzymatic activities was isolated. The location of the genes has been established by analyzing deletion derivatives, and the DNA sequence of 6.067 kilobases of the insert has been determined. Five open reading frames (ORFs) were found, one of which (ORF1; Mr 40,455) appears to code for a xylanase (XynA) which also acts on o-nitrophenyl-beta-D-xylopyranoside. Another, ORF5 (Mr 56,365), codes for a beta-xylosidase (XynB). The xynA gene product shows significant homology with the xylanases from the alkalophilic Bacillus sp. strain C125 and Clostridium thermocellum.     

Annexin-1 is an endogenous gastroprotective factor against indomethacin-induced damage

Adherence of neutrophils to the vascular endothelium is an early and critical event in the pathogenesis of gastric injury induced by NSAIDs. Pretreatment with glucocorticoids has been shown to prevent NSAID-induced neutrophil adherence and, in turn, to protect the stomach from injury. Some of the anti-inflammatory effects of glucocorticoids, including inhibition of neutrophil adherence, are mediated via the release of annexin-1. In this study, we assessed the contribution of annexin-1 to the protective actions of a glucocorticoid (dexamethasone) against indomethacin-induced gastric damage. Dexamethasone pretreatment markedly reduced the extent of indomethacin-induced gastric damage in rats. Immunoneutralization of annexin-1 resulted in a reversal of the gastroprotective actions of dexamethasone. Similarly, pretreatment with either of two antagonists of the formyl peptide receptor family, to which annexin-1 binds, reversed the gastroprotective effects of dexamethasone. The inhibitory effects of dexamethasone on indomethacin-induced leukocyte adherence in the mesenteric microcirculation were abolished by pretreatment with an antibody directed against annexin-1 or with an antagonist of the formyl peptide receptors. These results demonstrate that annexin-1 mediates the gastroprotective effects of a glucocorticoid against NSAID-induced damage. We propose that in some circumstances, annexin-1 plays an important role as an endogenous mediator of mucosal defense.     

Anchored plasticity opens doors for selective inhibitor design in nitric oxide synthase

Nitric oxide synthase (NOS) enzymes synthesize nitric oxide, a signal for vasodilatation and neurotransmission at low concentrations and a defensive cytotoxin at higher concentrations. The high active site conservation among all three NOS isozymes hinders the design of selective NOS inhibitors to treat inflammation, arthritis, stroke, septic shock and cancer. Our crystal structures and mutagenesis results identified an isozyme-specific induced-fit binding mode linking a cascade of conformational changes to a new specificity pocket. Plasticity of an isozyme-specific triad of distant second- and third-shell residues modulates conformational changes of invariant first-shell residues to determine inhibitor selectivity. To design potent and selective NOS inhibitors, we developed the anchored plasticity approach: anchor an inhibitor core in a conserved binding pocket, then extend rigid bulky substituents toward remote specificity pockets, which become accessible upon conformational changes of flexible residues. This approach exemplifies general principles for the design of selective enzyme inhibitors that overcome strong active site conservation.     

Folding and assembly of dimeric human glutathione transferase A1-1

Glutathione transferases function as detoxification enzymes and ligand-binding proteins for many hydrophobic endogenous and xenobiotic compounds. The molecular mechanism of folding of urea-denatured homodimeric human glutathione transferase A1-1 (hGSTA1-1) was investigated. The kinetics of change were investigated using far-UV CD, Trp20 fluorescence, fluorescence-detected ANS binding, acrylamide quenching of Trp20 fluorescence, and catalytic reactivation. The very early stages of refolding (millisecond time range) involve the formation of structured monomers with native-like secondary structure and exposed hydrophobic surfaces that have a high binding capacity for the amphipathic dye ANS. Dimerization of the monomeric intermediates was detected using Trp fluorescence and occurs as fast and intermediate events. The intermediate event was distinguished from the fast event because it is limited by a preceding slow trans-to-cis isomerization reaction (optically silent in this study). At high concentrations of hFKBP, dimerization is not limited by the isomerization reaction, and only the fast event was detected. The fast (tau = 200 ms) and intermediate (tau = 2.5 s) events show similar urea-, temperature-, and ionic strength-dependent properties. The dimeric intermediate has a partially functional active site ( approximately 20%). Final reorganization to form the native tertiary and quaternary structures occurs during a slow, unimolecular, urea- and ionic strength-independent event. During this slow event (tau = 250 s), structural rearrangements at the domain interface occur at/near Trp20 and result in burial of Trp20. The slow event results in the regain of the fully functional dimer. The role of the C-terminus helix 9 (residues 210-221) as a structural determinant for this final event is proposed.