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.     

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.     

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.     

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.     

Progressive defects observed in mouse sperm during the course of three generations of selenium deficiency

Three successive generations of mice were fed a Torula yeast based Se-deficient diet with or without 0.1 ppm Se in the drinking water. The Se-deficient mice, in the course of three generations, showed a decrease in body weight, testis weight, epididymal weight, and sperm production. The percentage of morphologically abnormal sperm increased in successive generations. The majority of sperm defects were found in the midpiece region of the tail. Many of these aberrant sperm were motile. A progressive decrease in fertility was noted during the first two generations of Se deficiency. This system confirms the essential role of Se in spermatogenesis and provides a model for the evaluation of the primary effect of Se deprivation on the structural development of sperm.     

Increased phosphorylation of the NR1 subunit of the NMDA receptor following cerebral ischemia

The effects of transient cerebral ischemia on phosphorylation of the NR1 subunit of the NMDA receptor by protein kinase C (PKC) and protein kinase A (PKA) were investigated. Adult rats received 15 min of cerebral ischemia followed by various times of recovery. Phosphorylation was examined by immunoblotting hippocampal homogenates with antibodies that recognized NR1 phosphorylated on the PKC phosphorylation sites Ser890 and Ser896, the PKA phosphorylation site Ser897, or dually phosphorylated on Ser896 and Ser897. The phosphorylation of all sites examined increased following ischemia. The increase in phosphorylation by PKC was greater than by PKA. The ischemia-induced increase in phosphorylation was predominantly associated with the population of NR1 that was insoluble in 1% deoxycholate. Enhanced phosphorylation of NR1 by PKC and PKA may contribute to alterations in NMDA receptor function in the postischemic brain.     

Ultraviolet Mutagenesis and Its Repair in an ESCHERICHIA COLI Strain Containing a Nonsense Codon

Ultraviolet mutagenesis and its repair were studied mainly in WU36-10-89, a uvr(-) strain of Escherichia coli containing a UAG mutation in a gene for leucine biosynthesis. Following ultraviolet (UV) irradiation revertants appearing with or without direct photoreactivation (PR) were classified according to the presence and type of suppressor they contained. We find UV mutation production to be quite specific. An analysis of revertants produced by UV indicates they are formed mainly from GC --> AT and that the miscoding is due to a cytosine residue at the site of mutation in a cytosine-thymine (CT) dimer. We propose that the dimer serves as template during some aspects of repair replication and at the time of replication the C in the dimer directs the insertion of A in the complementary strand. We also note that C --> A and T -->G changes caused by a CT dimer occur much less frequently.     

The effect of administering equine chorionic gonadotropin (eCG) and human chorionic gonadotropin (hCG) post artificial insemination on fertility of lactating dairy cows

The objective was to evaluate the effect of equine chorionic gonadotropin (eCG) and hCG post artificial insemination (AI) on fertility of lactating dairy cows. In Experiment 1, cows were either treated with eCG on Day 22 post AI (400 IU; n = 80) or left untreated (n = 84). On Day 29, pregnant cows were either treated with hCG (2500 IU; n = 32) or left untreated (n = 36). Pregnancy and progesterone were evaluated on Days 29 and 45. In Experiment 2, cows (n = 28) were either treated with eCG on Day 22 (n = 13) or left untreated (n = 15) and either treated with hCG on Day 29 (n = 14) or left untreated (n = 14). Blood sampling and ultrasonography were conducted between Days 22 and 45. In Experiment 3, cows were either treated with eCG on Day 22 post AI (n = 229) or left untreated (n = 241). Pregnancy was evaluated on Days 36 and 85. In Experiment 1, eCG on Day 22 increased (P < 0.02) the number of pregnant cows on Day 29 (50.0 vs. 33.3%) and on Day 45, the increase was higher (P < 0.01) in cows with timed AI (41.2 vs. 6.5%) than in cows AI at detected estrus (50.0 vs. 37.8%). Pregnancy losses were reduced by eCG and hCG, but increased in cows that did not receive eCG but were given hCG (P < 0.01). Treatment with hCG tended (P < 0.06) to increase progesterone in control cows, but not in cows treated with eCG. In Experiment 2, hCG increased (P < 0.01) the number of accessory CLs on Day 35 (28.5 vs. 0.0%) and tended (P < 0.07) to increase progesterone. In Experiment 3, eCG increased the number of pregnant cows (P < 0.05) on Days 36 and 85, but only in cows with low body condition (eCG = 45.6 and 43.5%; Control = 22.9 and 22.9%). In conclusion, eCG at 22 days post insemination increased fertility, primarily in cows with low body condition and reduced pregnancy losses when given 7 days before hCG; hCG induced accessory CLs and slightly increased progesterone, but hCG given in the absence of a prior eCG treatment reduced fertility.     

Alterations in the activity of phospholipases A2 in postmortem white matter from patients with multiple sclerosis

Activities toward arachidonyl-labelled phospholipase A₂ substrates were assayed in fractions of white matter and cerebral cortex from control subjects and in fractions of demyelinated plaque, normal-appearing white matter and cerebral cortex from subjects who died with multiple sclerosis. Membranous activity at pH 8.6 in the presence of Ca²⁺, characteristic of 14 kDa secretory phospholipase A₂, in either multiple sclerosis white matter or cortex did not differ from controls, whereas membranous activity at pH 4.5 in the absence of added Ca²⁺, characteristic of lysosomal enzymes was increased over controls in both plaque and normal-appearing white matter but not cerebral cortex. Activity in the cytosol fraction, at pH 8.6 in the presence of Ca²⁺ and glycerol characteristic of the cytosolic 85 kDa enzyme was decreased by greater than 50% in both white matter and cortex samples from multiple sclerosis subjects. Immuno-precipitation and-blotting confirmed that the deficient activity was largely attributable to the 85 kDa enzyme although the enzyme protein was not similarly reduced.Special issue dedicated to Dr. Leon S. Wolfe.