Inhibition of Escherichia coli B by homoarginine

Homoarginine inhibits the growth of Escherichia coli B, but not of E. coli K-12. These two strains also differ in regard to repressibility of the arginine-forming enzymes. In K-12, arginine acts as a repressor whereas in B it does not. The latter difference is determined by different alleles of a regulator gene, arg R. In K-12 × B crosses, it was shown that the genetic determinant for homoarginine sensitivity is closely linked to or identical with arg R. Homoarginine-resistant mutants of B were isolated. The biochemical mechanism of homoarginine inhibition is not known. However, whether or not a strain is sensitive to homoarginine seems to depend on the intracellular level of arginine. In B this level is relatively low and inflexible as a result of the action of a repressor whose formation is determined by the B-specific allele of arg R.     

Cerebrospinal fluid,plasma, and urinary MHPG in children

Cerebrospinal fluid (CSF) free MHPG levels for six autistic and four medicated Tourette Syndrome (TS) patients are in the usual adult range, but levels are elevated in two recently medicated TS patients. Plasma free MHPG levels in unmedicated autistic and TS patients are similar to those in normal boys, but are increased in two of seven medicated TS patients. There is a strong association between plasma free MHPG and urinary total MHPG levels in normal boys. Age and total urinary MHPG are positively correlated in autistic children. MHPG appears to be a useful index of noradrenergic function in childhood neuropsychiatric disorders.     

Noradrenergic stimulation in vivo increases (Na+, K+)-adenosine triphosphatase activity

In order to evaluate the role of norepinephrine in regulating activity of (Na⁺, K⁺)-ATPase in vivo, enzyme activity was measured in rat brain after electrical stimulation of the locus coeruleus and after administration of piperoxane. Both treatments resulted in increased (Na⁺, K⁺)-ATPase activity in locus coeruleus projection areas, but not in corpus striatum. The increased activity was limited to the same side as the stimulating electrode. Destruction of noradrenergic fibers from the locus coeruleus with 6-hydroxydopamine prevented the increase in enzyme activity with piperoxane.     

Habitat selection and patchiness in Scapholeberis: horizontal distribution and migration of S.mucronata in a small pond

The horizontal distribution of Scapholeberis mucronata in asmall pond was studied by transect and pattern sampling. Densitiesare high (>1000 animals m^–2) in the littoral zone andlow in the open water (no aquatic vegetation; <<50 animalsm^–2). The preference for the littoral zone is, however,less well expressed during the night, indicative of a diurnalhorizontal migration. Within the littoral zone, the distributionof Scapholeberis is highly aggregated. The relative degree ofpatchiness is inversely correlated with density. The relativeabundance of males and ephippial females was not invariablyhigher in than out of patches. It is hypothesized that the observedhabitat preference, as well as the aggregative behaviour, ofScapholeberis are mechanisms to avoid predation by fishes.     

Effects of Nematophagous Fungi on Numbers and Death Rates of Bacterivorous Nematodes in Arable Soil

In a series of microcosm experiments with an arable, sandy loam soil amended with sugarbeet leaf, the short-term (8 weeks) dynamics of numbers of nematodes were measured in untreated soil and in γ-irradiated soil inoculated with either a field population of soil microorganisms and nematodes or a mixed population of laboratory-propagated bacterivorous nematode species. Sugarbeet leaf stimulated an increase in bacterivorous Rhabditidae, Cephalobidae, and a lab-cultivated Panagrolaimus sp. Differences were observed between the growth rates of the nematode population in untreated and γ-irradiated soils, which were caused by two nematophagous fungi, Arthrobotrys oligospora and Dactylaria sp. These fungi lowered the increase in nematode numbers due to the organic enrichment in the untreated soil. We estimated the annually produced bacterivous nematodes to consume 50 kg carbon and 10 kg nitrogen per ha, per year, in the upper, plowed 25 cm of arable soil.     

Intratumoral low-dose interleukin-2 induces rejection of distant solid tumour

Summary This study shows that local tumour treatment with low-dose recombinant interleukin-2 (IL-2) can mediate rejection of a large distant solid tumour. When SL2 lymphoma cells were injected intraperitoneally (i.p.) in syngeneic DBA/2 mice on day 0, 70% of these mice were cured by daily i. p. injections with 20 000 units IL-2 on days 10–14. After injecting mice with SL2 both i.p. and subcutaneously (s. c.) on the flank, 50% of the mice treated i.p. with low-dose IL-2 rejected both the i.p. tumour and the large distant s.c. tumour. In contrast, i.p. IL-2 treatment on days 10–14 cured fewer than 10% of the mice bearing only a s. c. SL2 tumour. The described IL-2 immunotherapy also caused systemic tumour rejection in mice bearing both ascitic and solid P815 mastocytoma. Thus it was shown that low-dose IL-2 can induce systemic tumour rejection, when injected at a site of tumour growth. Interleukin-2-induced rejection of s. c. SL2 tumour was highly specific, as mice that were rejecting i.p. and solid s. c. SL2 lymphoma did not reject solid P815 mastocytoma, which was injected s.c. simultaneously on the other flank. Furthermore, solid s.c. tumours consisting of mixtures of SL2 and P815 were not rejected in mice that rejected i.p. SL2 or P815. We conclude that intratumoral injections of low-dose IL-2 can enhance an ongoing weak immune reaction against the tumour resulting in systemic tumour rejection.     

Salinity effects on CO2 assimilation and diffusive conductance of cowpea leaves

The effect of NaCl salinity at concentrations of 43–173 mM in nutrient solution on net gas exchange of attached cowpea [Vigna unguiculata (L.) Walp cv. California Black-eye No. 5 (CB5)] leaves was investigated under both greenhouse and growth chamber conditions.
There was a marked decrease in leaf conductance to water vapor after exposure to low salinity levels and a slighter decrease when salinity levels were higher. The decrease in net assimilation was much more gradual throughout the entire salinity range. The altered responses of net assimilation and leaf conductance to salinity were more evident at a high light intensity. A decrease in intercellular partial CO₂ pressure [p(CO₂)] was found at the low and intermediate salinity levels but not at the high level. These findings suggest that CO, assimilation was mainly controlled by stomatal conductance and the fixation of CO, might have been increased due to stimulated biochemical activity or to higher chlorophyll concentration per unit leaf area. A decrease in assimilation was already found one day after salinization and pro-ceeded up to 4 days when it was inhibited by 50% at 43 mM NaCl and up to 85% at 173 mM. The decrease in transpiration was larger than the decrease in net assimila-tion, and both were attributed to osmotic stress. Partial recovery was found thereaf-ter and new steady-state rates, in the range of 55 to 100% of the control, were then obtained for salinity levels between 43 and 130 mM. Inhibition of net CO, assimila-tion at this stage was attributed partly to a specific sodium effect and partly to plant water status. A linear relationship between leaf sodium content and net photosynthe-sis was also evident at this stage. Net CO, assimilation recovered more completely than transpiration when salt stress was removed, but at 173 mM NaCl recovery was neglible.     

Comparison of FDR- and SDR-derived tetraploid progeny from 2x×4x crosses using haploids of Solanum tuberosum L. that produce mixed modes of 2n eggs

 The relationship between heterozygosity and heterosis in tetraploid potato (Solanum tuberosum subsp. tuberosum L., 2n=4x=48) was examined in a series of first-division restitution (FDR)- and second-division restitution (SDR)-derived tetraploid subpopulations. The subpopulations were constructed using two 2n egg-producing, mixed-mode haploids (2n=2x=24) crossed to three tetraploid (2x= 4x=48) potato clones. Half-tetrad analysis using a co-dominant electrophoretic marker (Pgm-2), which is closely linked to the centromere, discriminated between FDR- and SDR-derived 4x progeny. The FDR:SDR ratio of the 4x progeny observed was dependent upon the haploid parent used in the 2x×4x cross. Field studies were conducted between 1992 and 1996 to compare the yield and specific gravity of the two subpopulations and their parents from three crosses. There was no difference in the total tuber yield or specific gravity between the FDR- and SDR-subpopulations based upon family means, despite the expectation that FDR-derived progeny would transmit a greater portion of the genome’s heterozygosity intact than SDR-derived progeny. The 4x parent in each family had a higher yield than either 4x progeny subpopulation. Inbreeding, as a consequence of the haploidization process and a lack of genetic diversity, may have negated any advantage of the FDR-derived progenies over the SDR-derived progenies. Received: 14 April 1998 / Accepted: 12 May 1998