Influence of very low doses of ionizing radiation on Synechococcus lividus metabolism during the initial growth phase

Previous results from this laboratory have shown that very low chronic doses of gamma radiation can stimulate proliferation of the Cyanobacterium Synechococcus lividus. This modification of cell proliferation occurred during the first doubling. In this paper, we have compared the metabolism of cells cultivated in a normal environment or under chronic irradiation. Incubation of the cells in a new medium induced a high superoxide dismutase (EC 1.15.1.1, SOD) activity at the 18th hour and a degradation of phycocyanin, thus demonstrating that cells were submitted to a photooxidative stress. This increase in superoxide dismutase activity was followed by concomittant peaks of glutathione reductase (EC 1.6.4.2, GR) and glucose-6-phosphate dehydrogenase (EC 1.1.1.49, G6P-DH) at the 24th hour. Irradiated cultures at a dose of 53.5 mGray/year show an earlier and higher peak of SOD, GR, and G6P-DH. In a second stage, cultures showed an earlier onset of photosynthesis under irradiation, as evidenced by an increase in pigment content and an enhancement of glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.13, GAP-DH). These results show that the radiostimulation is related to the activation of enzymes protecting against peroxides that were induced under oxidative circumstances and to the activation of a glucose catabolism via the oxidative pentose phosphate pathway.Abbreviations mGy milli-Gray - SOD superoxide dismutase - G6P-DH glucose-6-phosphate dehydrogenase - GAP-DH glycer-aldehyde-3-phosphate dehydrogenase - GSSG oxidized glutathione     

Irreversible Activation of the Opiate Receptor of Neuroblastoma × Glioma Hybrid Cells by an Alkylating Benzomorphan Derivative

The benozomorphan derivative (-)-2-[2-(p-bromoacetamidophenyl)ethyl]-5,9 alpha-dimethyl-2'-hydroxy-6,7-benzomorphan (BAB), capable of reacting with nucleophilic groups, acts on neuroblastoma X glioma hybrid cells as a potent, irreversible opiate agonist. Its potency in inhibiting the increase in cellular cyclic AMP, evoked by prostaglandin E1, is comparable to that of Leu-enkephalin. This also applies to its capacity to compete with [3H]D-Ala2-Met-enkephalinamide ([3H]DAEA) in binding on cell membrane preparations. The comparatively lower potency of (-)-2-[2-(p-acetamidophenyl)-ethyl]-5,9 alpha-dimethly-2'-hydroxy-5,7-benzomorphan (AB), which differs from BAB in the substitution of the bromoacetamido group by an acetamido group, is of the same order of magnitude as that of morphine. The covalent interaction of BAB with the opiate receptors is deduced from the observations that (1) it is not possible to wash away this compound from the receptors, (2) the potency of BAB in inhibiting the specific binding of [3H]DAEA increases with prolonged preincubation time, and (3) AB behaves as a reversible agonist.     

The effects of ultraviolet-B radiation on plant competition in terrestrial ecosystems

Evidence regarding the interaction of ultraviolet-B (UV-B, 280-320 nm) radiation and plant competition in terrestrial ecosystems is examined. The competitive interactions of some species pairs were affected even by ambient solar UV-B radiation (as exists without ozone depletion), when compared to control pairs grown without UV-B. Also, the total shoot biomass of these species pairs was depressed under ambient UV-B. Relatively large increases in UV-B radiation (approximating a 40% ozone layer reduction when weighted with the generalized plant action spectrum) altered the competitive interactions of some species pairs grown in pots under field conditions, but did not affect the total shoot biomass production of those pairs. Recent field experiments have examined the competitive interactions of wheat ( Triticum aestivum L. cv. Bannock) and wild oat ( Avena fatua L.) under a simulated increased UV-B regime resulting from a 16% ozone layer reduction when weighted with the generalized plant action spectrum. This increase in UV-B altered the competitive interactions of these two species without affecting the total shoot biomass production of the species pair. The manner in which increased UV-B affected the relative competitive abilities of the two species was highly dependent upon the environmental conditions during the early life stages of the plants. The implications of these results for both agricultural and natural plant communities are discussed.     

The 60S ribosomal subunit is altered in the skeletal muscle of dystrophic hamsters

Polysomes from the skeletal muscle of normal and dystrophic hamsters were dissociated into ribosomal subunits by treatment with puromycin and the subunits from both strains were reassociated in all possible combinations. When their protein synthesis activity was assayed in a poly(U)-directed cell-free system at a low magnesium concentration, the reassociated ribosomes from dystrophic hamsters were less active than the ribosomes from control animals. The ribosomal defect is a property of the 60S subunit and is due to a ribosomal component rather than to abnormal binding of a non-ribosomal protein.     

Some USDA studies on the soybean-Rhizobium symbiosis

Summary The ecology, strain evaluation, genetics of host strain interactions and physiology of nitrogen fixation ofRhizobium japonicum in association with the soybean,Glycine max, were studied. Results of inoculation experiments with selected strains ofRhizobium japonicum indicated that indigenous strains occupied most of the nodules of soybeans grown in highRhizobium japonicum populated soils. Nodule sampling indicated that inoculation did not result in quicker nodulation or a higher incidence of root nodules (primary or secondary) than uninoculated checks. Rhizosphere studies indicated that colonization by introduced strains did occur but did not compete successfully with field strains for nodule sites. Recovery of specific serological types from nodules was influenced by planting intervals. The distribution of the serotypes varied with the time of planting and the age of the plant. Temperature studies indicated that the distribution of serotypes recovered from the nodules was influenced by temperature. Field studies showed the selectivity of soybean genotypes on strains ofRhizobium japonicum. Some strains were more common in the nodules of some varieties than in others. Closely related varieties had similar populations in their nodules. Three genes which control nodule response in soybeans are reported. Nitrogen fixation profiles were determined for some variety-strain interactions. Combinations previously classified as inefficient showed some nitrogenase activity as measured by the acetylene reduction technique. Research Microbiologist; Research Agronomist; Research Plant Physiologist, Soybean Investigations, Crops Research Division, Beltsville, Md. (USDA, ARS); and Plant Pathologist currently located at Michigan State University, East Lansing, Michigan.     

Inorganic and Metal-Organic Growth Requirements of the Genus Bacteroides

The inorganic and metal-organic growth requirements of ruminal and nonruminal Bacteroides species were compared. The heme requirement of many nonruminal Bacteroides species was similar to that of Bacteroides ruminicola subsp. ruminicola and was a general tetrapyrrole requirement. Some nonruminal Bacteroides species utilized succinate or alpha-ketoglutarate, as well as tetrapyrrole-containing compounds, in place of heme. Fe(+) as well as heme was required for maximal yields of some Bacteroides species. The divalent cation requirements of Bacteroides species are complex. Mg(2+) deletion from a medium containing Mg(2+), Ca(2+), Co(2+), and Mn(2+) reduced the yields of all isolates. Ca(2+) deletion from the same medium reduced the growth yields of Bacteroides fragilis, B. fundiliformis, and one strain of B. oralis. The effects of Mg(2+) and Ca(2+) on the growth of Bacteroides isolates was influenced by other divalent cations. Relatively large quantities of Na(+) were obligately required by all of the currently recognized predominant rumen Bacteroides species. Nonruminal Bacteroides species either did not require Na(+) or required only small amounts. The Na(+) requirement of some nonruminal Bacteroides species could be partially replaced by Li(+) or Cs(+). The Na(+) requirement of rumen Bacteroides species was absolute. The inorganic and metal-organic growth requirements of Bacteroides species appear useful as aids in species differentiation.     

Possible mode of action of a photosynthetic inhibitor produced byPandorina morum

The mode of action of the photosynthetic inhibitor produced byPandorina morum was examined by exposingVolvox globator and isolated spinach chloroplasts to a partially purified inhibitor preparation. Oxygen evolution ofVolvox, whole chloroplasts, and broken chloroplasts (-Calvin cycle) was reduced indicating that the substances inhibit the light reactions of photosynthesis. Oxygen evolution studies of other Volvocaceae confirmed the observation thatPandorina morum is not significantly influenced by its own inhibitor. Molecular weight approximation by gel filtration established that the inhibitor has a low, molecular weight (probably below 100 mw).