Effects of simulated fire on vesicular-arbuscular mycorrhizae in pinyon-juniper woodland soil

Effects of fire on vesicular-arbuscular mycorrhizal fungi were tested using microcosms constructed from soil, litter, and duff collected beneath canopies of pinyon pine, Utah juniper, and in the open space (interspace). Burning was conducted over wet and dry soils. Soil temperatures were monitored continuously throughout the microcosms during burning. Plants grown in soils burned when dry had a lower VAM colonization than soils burned when wet. Juniper soils demonstrated the greatest reduction, over 95%, compared to their respective controls. Plants grown in interspace soils burned when wet were least affected. There was a positive correlation (r²=0.90) between the decrease in VAM colonization and the soil temperature as a result of the fire. Temperature effects, and associated reductions in VAM, were related to amount of litter burned in each microcosm and the moisture content of the soils.     

Isolation and characterization of sporulation-specific promoters in the yeast Saccharomyces cerevisiae

A library of random yeast genomic DNA:lacZ fusions has been constructed using an episomal yeast-Escherichia coli shuttle vector (pCS1). Plasmid pCS1 requires insertion of a promoter and an in frame ATG codon upstream of its resident truncated lacZ gene to regulate expression in yeast. Yeast genomic DNA fragments of 4-6 kb were generated by partial digestion with Sau3A and ligated into the unique BamHI site of plasmid pCS1 to generate a library of 5 x 10(4) individual E. coli transformants. This library was screened to identify promoter-lacZ fusions that were expressed uniquely during sporulation. Of 342 yeast transformants that exhibited beta-galactosidase activity, two were found to express the lacZ gene in a sporulation-specific manner. This paper presents the characterization of two genomic yeast DNA fragments containing promoters that control lacZ expression during the sporulation process. Expression from the promoter present in plasmid pJC18 occurred from 11-21 hours into the sporulation process, while the promoter in plasmid pJC217 was active from 4-14 hours. Staining of nuclear DNA to correlate nuclear morphology with timing of gene expression showed when each of these promoters was active in terms of the morphological stages of sporulation.     

Estrogen receptor expression in serially cultivated rat endometrial cells: stimulation by forskolin and cholera toxin

Serially propagated with 3T3 feeder layer support, epithelial cells derived from normal rat endometrium expressed estrogen receptor activity. Specific binding of 17-beta-estradiol was in the range of 30-60 fmol/mg of protein and was of high affinity (Kd = 0.3 nM). A survey of cell lines derived from several other normal epithelia showed that rat vaginal and human cervical cultures also had high-affinity estrogen receptors (6-13 fmol/mg of protein), while rat epidermal and esophageal cells had no detectable activity. In the endometrial cultures, receptor levels were elevated nearly two- to fourfold by cholera toxin or forskolin in the medium. This effect was detectable after 4 hr but not 1 hr of treatment and did not occur in the presence of cycloheximide. We conclude that serially cultivated rat endometrial cells retain hormonal properties expressed in vivo while exhibiting some keratinocyte character. These cells may provide a useful model for study of receptor modulation.     

Copper ions and hydrogen peroxide form hypochlorite from NaCl thereby mimicking myeloperoxidase

Sea urchins have elaborated multiple defenses to assure monospermic fertilization. In this work, we have concentrated on a study of the mechanism(s) by which hydrogen peroxide (H₂O₂) prevents polyspermy in Arbacia punctulata. We found that it is not H₂O₂ but probably hypochlorous acid/hypochlorite (HOCl/OCl^?) derived from H₂O₂ that is toxic to the supernumerary sperm. The spermicidal activity of H₂O₂ is potentiated by at least one order of magnitude by cupric ions (Cu²⁺). This increased toxicity is not due to the formation of hydroxyl radicals (·OH) because ·OH scavengers did not counteract the activity of Cu²⁺. More-over, substitution of Cu²⁺ by ferrous ions (Fe²⁺), which are known to cause formation of ·OH from H₂O₂, had no effect on fertilization even at 10²?10³ times higher concentrations. In contrast, 3-amino-1,2,4-triazole (AT), an HOCl/OCl^? scavenger, totally reversed the toxic effects of Cu²⁺. Furthermore, we found that HOCl/OCl^? is generated in solutions of H₂O₂ and Cu²⁺ in the presence of 0.5 M NaCl and that its accumulation is abolished by AT. Thus it is possible that the antifertility properties of copper are due to its ability to mediate formation of HOCl/OCl^?. HOCl/OCl^? generated by Cu²⁺ from H₂O₂ and Cl^?, a low concentration of exogenously added HOCl/OCl^?, or increased concentrations of H₂O₂ has similar inhibitory effects on the fertilization process in sea urchins. Therefore, we suggest that polyspermy is prevented by the action of a myeloperoxidase that affects the formation of HOCl/OCl^? from the Cl^? present in sea water through reaction with H₂O₂ generated by the newly fertilized egg.     

Dye permeability at phase transitions in single and binary component phospholipid bilayers

By encapsulating a pH-sensitive dye, phenol red, in multilamellar liposomes of DMPC, DPPC and DMPC/DPPC mixtures, the permeability of these phospholipid bilayers to dye as a function of temperature has been studied. For both DMPC and DPPC liposomes, dye release begins well below the main gel-to-liquid-crystalline phase transition (24°C and 42°C, respectively) at temperatures corresponding to the onset of the pretransition (about 14°C and 36°C, respectively) with DPPC liposomes exhibiting a permeability anomaly at the main phase transition (42°C). The perturbation occurring in the bilayer structure that allows the release of encapsulated phenol red (approx. 5 Å diameter) is not sufficient to permit the release of encapsulated haemoglobin (approx. 20 Å diameter, negatively charged). In liposomes composed of a range of DMPC/DPPC mixtures, dye release commences at the onset of the pretransition range (determined by optical absorbance measurements) and increases with increasing temperature until the first appearance of liquid crystalline phase after which no further dye release occurs. Interestingly, the dye retaining properties of DMPC and DPPC liposomes well below their respective pretransition temperature regions are very different: DMPC liposomes release much encapsulated dye at incubation temperatures of 5°C whilst DPPC liposomes do not.     

PLASTID DEVELOPMENT IN IOJAP- AND CHLOROPLAST MUTATOR-AFFECTED MAIZE PLANTS

Plastids affected by either iojap or chloroplast mutator fail to green, and altered plastids are maternally transmitted to subsequent generations. The ultrastructure of iojap-affected plastids indicates that these plastids contain no ribosomes and are capable of supporting little internal membrane organization in either light or dark-grown plants. Chloroplast mutator-affected plastids of light-grown plants contain some organized internal membrane structures. In dark-grown plants, chloroplast mutator-aftected plastids contain a crystalline prolamellar body, numerous vesicles, and osmiophilic granules. The chloroplast mutator-affecled etioplasts display an abnormal distribution of lamellar membranes; these membranes, rather than radiating in a spokelike pattern from the prolamellar body, are condensed into a portion of the organelle. Light causes disruption of the prolamellar body in chloroplast mutator-affected plastids without promoting the organization of a normal thylakoid membrane system. The effects of iojap and chloroplast mutator are cell autonomous and apparently influence the individual plastid, as evidenced by the persistence of heteroplastidic cells containing normal and affected plastids.     

Book Reviews

Book reviewed in this article:
ARCHEOLOGY: Papers of the New World Archaeological Foundation
No. 6. The Carved Human Femurs from Tomb 1, Chiapa de Corzo, Chiapas, Mexico . P ierre A grinier
No. 7. Archaeological Explorations in the Region of the Frailesca, Chiapas, Mexico . C arlos N avarrete
Nos. 8–11. Excavations at Chiapa de Corzo, Chiapas, Mexico . G areth W. L owe
No. 12. Mound 5 and Minor Excavations, Chiapa de Corzo, Chiapas, Mexico . G areth W. L owe
No. 13. Ceramic Stratigraphy at Santa Cruz, Chiapas, Mexico . W illiam T. S anders
No. 14. The Santa Marta Rock Shelter, Ocozocoautla, Chiapas, Mexico . R ichard S. M ac N eish and F redrick A. P eterson