Bleomycin resistance: a new dominant selectable marker for plant cell transformation

Summary Plant cells are sensitive to the antibiotic bleomycin, a DNA damaging glycopeptide. A bleomycin resistance determinant, located on transposon Tn5 and functional in bacteria, has been cloned in a plant expression vector and introduced into Nicotiana plumbaginifolia using Agrobacterium tumefaciens. The expression of this determinant in plant cells confers resistance to bleomycin and allows selection of transformed plant cells.     

Congenital toxoplasmosis: epidemiologic features and control.

Toxoplasmosis is caused by the parasite Toxoplasma gondii. It is acquired from undercooked meat or from food or fomites contaminated by cat feces. The disease can be transmitted to the fetus only during maternal parasitemia, which is associated with primary infection. Extrapolation from current data suggests that there are 140 to 1400 cases of congenital toxoplasmosis per year in Canada and that 70 to 280 of the infants are severely affected at birth; many of the others suffer sequelae later in life. Serologic diagnosis of primary infection in the mother is quite sensitive and specific. Diagnosis in the infant is more difficult and may take several months. Prenatal treatment of the woman and postnatal treatment of the infant are hampered by the lack of proven efficacy as well as ethical and compliance problems. Preventive serologic screening and prophylaxis have the same drawbacks. Educating young women to avoid infection is an inexpensive, low-risk intervention that would be the preferred preventive strategy if it could be shown to be effective. Immunization may prove to be the most cost-effective method of preventing congenital toxoplasmosis if a safe and effective vaccine is developed.     

Association between coated vesicles and microtubules

In this study, a possible functional association between microtubules and coated vesicles is described. We have found that our preparations of microtubules contained coated vesicles in quantities of usually above 10%. These coated vesicles were identified both by immunological methods using anticoat antibodies and by electron microscopy of negatively stained specimens. In the immune replica, two components of coated vesicles, i.e., heavy (clathrin) and light chains, were recognized as constituents of the preparations. In the electron microscope, it was found that coated vesicles were attached predominantly along the length of microtubules. Furthermore, projections from the microtubules to the triskelion centers of the clathrin lattice were identified and thus seem to serve as linkers between the cytoskeletal structure of the organelle. A similar type of association was detected in tissue culture cells; bridges between coated vesicles and microtubules were clearly identified by electron microscopy of thin sections.     

Nalorphine: actions at an opiate receptor on frog skeletal muscle fibers

Intracellular microelectrode studies were conducted to investigate the actions of the partial agonist-antagonist nalorphine at an opiate receptor on functional frog skeletal muscle fiber membranes. In high bath concentrations (greater than or equal to 10(-4) M), nalorphine alone produces agonist actions similar to the "full" opiate agonists. These actions were (i) to depress both the sodium and potassium (gNa and gK) conductance increases due to electrical stimulation by a nonspecific local anestheticlike mechanism and (ii) to depress gNa by a specific opiate receptor mediated mechanism. In a much lower bath concentration (1 X 10(-8) M) nalorphine acts to antagonize the specific opiate receptor mediated depression of gNa produced by the "full" agonist meperidine. Thus in this preparation nalorphine, "the partial antagonist," has the same actions as naloxone, which is often considered to be a full antagonist. The quantitative differences observed in the effects of these two opiate antagonists are discussed.     

Galactitol accumulation by glucose-6-phosphate deficient fibroblasts: a cellular model for resistance to the complications of diabetes mellitus

When incubated in high galactose media, fibroblasts from individuals with the severe (Mediterranean) variety of glucose-6-phosphate dehydrogenase (G6PD) deficiency accumulate significantly less galactitol than do fibroblasts from matched control subjects. The effect is not observed in fibroblasts from black subjects with the more common, and milder, A- variant of G6PD deficiency. Since aldose reductase and sorbitol dehydrogenase activities in experimental and control fibroblasts are identical, the effect is most likely due to the substantial reduction in NADPH levels in severely G6PD-deficient cells. Sorbitol does not accumulate either in control or in G6PD deficient fibroblasts incubated in high glucose medium, most likely because of the action of sorbitol dehydrogenase, and the presence of a carrier-mediated glucose transport system in the cell membrane which limits the concentration of glucose that can accumulate in these cells.     

ORGANIC COMPOUNDS RELEASED FROM A NATURAL POPULATION OF EPIBENTHIC BLUEGREEN ALGAE1

Extracellular release of dissolved organic compounds by the bluegreen algal community of a brackish marsh was studied using ¹⁴C techniques. Mannitol and trehalose were identified as the most commonly released compounds. The proportions of these two extracellular compounds varied in response to light intensity and the water potential of the environment. The presence of mannitol, in particular, suggests that excretion of organic compounds in natural situations is a function of osmotic adjustment.     

Enhanced binding of radioligands to receptors of γ-aminobutyric acid and benzodiazepine by a new anticonvulsive agent,LY81067

A diaryltriazine, LY81067, effectively protects against pentylenetetrazole- and picrotoxin-induced convulsions in mice, with ED₅₀ values of 5.7 and 5.8 mg/kg i.p., respectively. LY81067 enhances the binding of both ³H-GABA and ³H-flunitrazepam to specific sites in rat brain membranes. The degree of enhancement by LY81067 varies from one brain region to another and is different for the binding of ³H-GABA and ³H-flunitrazepam. In cortical membranes, LY81067 increases the affinity of ³H-GABA for both high and low affinity sites and increases the number of sites. LY81067 increases the affinity of ³H-flunitrazepam for its binding sites without greatly increasing the number of sites. Like the pyrazolopyridines, the enhancement of ³H-flunitrazepam binding by LY81067 is dependent on chloride or related anions and is reversed by picrotoxin, suggesting that LY81067 exerts its anticonvulsant effects by binding to or near picrotoxin binding sites. The differential effects of LY81067 on the enhancements of ³H-GABA and ³H-flunitrazepam binding in several brain regions suggest extensive multiplicity of GABA/benzodiazepine/picrotoxin/anioin receptor complexes.     

Metabolism of zinc and copper in the neonate: Zinc thionein in developing rat brain,heart, lung,spleen, and thymus

In a continuing study of the importance of metallothionein (MT) in the growth and development of neonates, zinc and copper metabolism in rat brain, heart, lung, spleen, and thymus has been analyzed in 5, 10, 15, 20 and 25 day old rats. Total, cytosol, and MT zinc and copper concentrations and organ contents were determined. Zinc, but very little, if any copper was associated with MT in these organs. Concentrations ranged from 0.03 to 3.3 μg Zn in MT/g; organ contents ranged from 0.003 to 2.2 μg Zn in MT/organ. Brain exhibited the highest concentrations and contents of zinc in MT, approaching the levels found in kidneys. Rank order of organ contents of zinc in MT was brain > lung > heart, spleen, thymus, during this neonatal growth period. When organ growth was rapid, a large percentage (20–95%) of the cytosolic zinc present in these organs was associated with MT, as has been previously observed with liver, kidneys, and testes. None of these organs undergoes the dramatic changes in zinc and copper metabolism previously observed in neonatal rat liver and gastrointestinal tract, and in maturing testes. They are more comparable to kidneys in their concentrations of zinc in MT. Like testes, little copper is found in these organs.     

Effects of flooding on leaf litter decomposition in microcosms

Summary The effects of hydroperiod on decomposition rates of senescent Acer rubrum leaves were tested in microcosms in a controlled laboratory environment. Microcosm treatments included continuously flooded, continuously unflooded, and fluctuating hydroperiods. All flooding treatments promoted decomposition but variations in hydroperiod had no significant effects. A leaching experiment indicated the higher decay rates under flooded conditions were primarily due to high leaching losses from soaking. Unlike nutrient dynamics in the field, where net accumulation occurs, nitrogen and phosphorus in the litter in the microcosms exhibited net losses. The major external inputs which provide a source of nitrogen and phosphorus for immobilization in the field were lacking in the microcosms. Calcium, magnesium, and potassium exhibited net losses except for calcium in the unflooded microcosms. The microcosm results demonstrated the importance of external inputs to litter nutrient relations.