O-acetyl-salicylic acid promotes colony formation from protoplasts of an elite maize inbred

The salicylic acid derivative acetylsalicylic acid (ASA) was found to promote colony formation from protoplasts isolated from embryogenic suspension cultures of an elite maize inbred line. The drug was most effective at concentrations of 30–100 mg/l, and increases of more than 20-fold in the number of colonies recovered from protoplasts were obtained. The rate of growth of protoplast-derived cell colonies was not affected.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - DMSO dimethylsulfoxide - KM Kao and Michayluk medium (1975) - MES 2[N-morpholino]ethanesulfonic acid - ASA acetylsalicylic acid     

Dominant expression of an amino-acid uptake deficiency in carrot somatic fusion hybrids

Somatic hybrids were selected previously by their ability to grow in medium containing normally inhibitory levels of the two amino acid analogs aminoethylcysteine (AEC) and 5-methyltryptophan (5MT) following fusion of protoplasts from a cell strain resistant to AEC with protoplasts resistant to 5MT. The hybrid nature of the selected clones was shown by several criteria including the presence of another resistance, azetidine-2-carboxylate (A2C), carried by one of the parental strains which was not selected for in the initial hybrid selection scheme. The characterization presented here shows that the AEC resistance in the parental strain, as well as the two somatic hybrids, was due to decreased AEC uptake. Also the 5MT resistance in the hybrids, as in the parent was caused by a feedback altered form of the tryptophan biosynthetic control enzyme, anthranilate synthase which leads to increases in free tryptophan. The A2C resistance was caused by the accumulation of free proline by a mechanism which has not been studied. These studies confirm that AEC resistance caused by decreased uptake can be expressed dominantly in protoplast fusion hybrids.Abbreviations A2C Azetidine-2-carboxylate - AEC Aminoethylcysteine - 5MT 5-methyltryptophan     

Postpartum reproductive performance in the multiparous mare fed to obesity

Twenty multiparous Quarter Horse mares were assigned to one of two treatment groups at 40 to 75 d of pregnancy. Group 1 was the control group and the mares were fed to maintain a moderate degree of body fat (condition score 5.5 to 7). Group 2 was the obese group and the mares were fed to achieve (prepartum) and then maintain (post partum) an extremely high degree of body fat (condition score 9). Estrous intensity was evaluated using subjective teasing scores ranging from 0 (rejection) to 4 (maximum receptivity). Mares were artificially inseminated beginning with the second postpartum ovulatory cycle; the study was terminated after 63 d of pregnancy. Duration of estrus, maximum teasing score and the number of mares exhibiting overt estrus (teasing score > 2) did not differ between treatment groups during the first and second postpartum ovulatory cycles. The intervals from foaling to first cycle ovulation, foaling to second cycle ovulation, and first to second cycle ovulation were also similar between treatment groups. All mares in both treatment groups conceived and maintained pregnancy. The first cycle conception rate and the number of cycles per conception did not differ between treatment groups. A high degree of body fat produced by overfeeding during gestation did not adversely affect postpartum reproductive performance in the multiparous mare.     

The rabbit alpha-like globin gene cluster is polymorphic both in the sizes of BamHI fragments and in the numbers of duplicated sets of genes

The alpha-like globin gene cluster in rabbits contains embryonic zeta- globin genes, an adult alpha-globin gene, and theta-globin genes of undetermined function. The basic arrangement of genes, deduced from analysis of cloned DNA fragments, is 5'-zeta 0-zeta 1-alpha 1-theta 1- zeta 2-zeta 3-theta 2-3'. However, the pattern of restriction fragments containing zeta- and theta-globin genes varies among individual rabbits. Analysis of BamHI fragments of genomic DNA from 24 New Zealand white rabbits revealed eight different patterns of fragments containing zeta-globin genes. The large BamHI fragments containing genes zeta 0 and zeta 1 are polymorphic in length, whereas a 1.9-kb fragment containing the zeta 2 gene and the 3.5-kb fragment containing the zeta 3 gene do not vary in size. In contrast to this constancy in the size of the restriction fragments, the copy number of the zeta 2 and zeta 3 genes does vary among different rabbits. No length polymorphism was detected in the BamHI fragments containing the theta-globin genes, but again the copy number varies for restriction fragments containing the theta 2 gene. The alpha 1- and theta 1-globin genes are located in a nonpolymorphic 7.2-kb BamHI fragment. The combined data from hybridization with both zeta and theta probes shows that the BamHI cleavage pattern does not vary within the region 5'-alpha 1-theta 1- zeta 2-zeta 3-theta 2-3', but the pattern genomic blot-hybridization patterns for the progeny of parental rabbits with different zeta-globin gene patterns shows that the polymorphic patterns are inherited in a Mendelian fashion. Two different haplotypes have been mapped based on the genomic blot-hybridization data. The variation in the alpha-like globin gene cluster in the rabbit population results both from differences in the copy number of the duplication block containing the zeta-zeta-theta gene set and from the presence or absence of polymorphic BamHI sites.      

C1 metabolism inParacoccus denitrificans: Genetics ofParacoccus denitrificans

Paracoccus denitrificans is able to grow on the C₁ compounds methanol and methylamine. These compounds are oxidized to formaldehyde which is subsequently oxidized via formate to carbon dioxide. Biomass is produced by carbon dioxide fixation via the ribulose biphosphate pathway. The first oxidation reaction is catalyzed by the enzymes methanol dehydrogenase and methylamine dehydrogenase, respectively. Both enzymes contain two different subunits in an ₂₂ configuration. The genes encoding the subunits of methanol dehydrogenase (moxF andmoxI) have been isolated and sequenced. They are located in one operon together with two other genes (moxJ andmoxG) in the gene ordermoxFJGI. The function of themoxJ gene product is not yet known.MoxG codes for a cytochromec _551i , which functions as the electron acceptor of methanol dehydrogenase. Both methanol dehydrogenase and methylamine dehydrogenase contain PQQ as a cofactor. These so-called quinoproteins are able to catalyze redox reactions by one-electron steps. The reaction mechanism of this oxidation will be described. Electrons from the oxidation reaction are donated to the electron transport chain at the level of cytochromec. P. denitrificans is able to synthesize at least 10 differentc-type cytochromes. Five could be detected in the periplasm and five have been found in the cytoplasmic membrane. The membrane-bound cytochromec ₁ and cytochromec ₅₅₂ and the periplasmic-located cytochromec ₅₅₀ are present under all tested growth conditions. The cytochromesc _551i andc _553i , present in the periplasm, are only induced in cells grown on methanol, methylamine, or choline. The otherc-type cytochromes are mainly detected either under oxygen limited conditions or under anaerobic conditions with nitrate as electron acceptor or under both conditions. An overview including the induction pattern of allP. denitrificans c-type cytochromes will be given. The genes encoding cytochromec ₁, cytochromec ₅₅₀, cytochromec _551i , and cytochromec _553i have been isolated and sequenced. By using site-directed mutagenesis these genes were mutated in the genome. The mutants thus obtained were used to study electron transport during growth on C₁ compounds. This electron transport has also been studied by determining electron transfer rates inin vitro experiments. The exact pathways, however, are not yet fully understood. Electrons from methanol dehydrogenase are donated to cytochromec _551i . Further electron transport is either via cytochromec ₅₅₀ or cytochromec _553i to cytochromeaa ₃. However, direct electron transport from cytochromec _551i to the terminal oxidase might be possible as well. Electrons from methylamine dehydrogenase are donated to amicyanin and then via cytochromec ₅₅₀ to cytochromeaa ₃, but other routes are used also.P. denitrificans is studied by several groups by using a genetic approach. Several genes have already been cloned and sequenced and a lot of mutants have been isolated. The development of a host/vector system and several techniques for mutation induction that are used inP. denitrificans genetics will be described.     

Trimethyloxonium modification of single batrachotoxin-activated sodium channels in planar bilayers. Changes in unit conductance and in block by saxitoxin and calcium

Single batrachotoxin-activated sodium channels from rat brain were modified by trimethyloxonium (TMO) after incorporation in planar lipid bilayers. TMO modification eliminated saxitoxin (STX) sensitivity, reduced the single channel conductance by 37%, and reduced calcium block of inward sodium currents. These effects always occurred concomitantly, in an all-or-none fashion. Calcium and STX protected sodium channels from TMO modification with potencies similar to their affinities for block. Calcium inhibited STX binding to rat brain membrane vesicles and relieved toxin block of channels in bilayers, apparently by competing with STX for the toxin binding site. These results suggest that toxins, permeant cations, and blocking cations can interact with a common site on the sodium channel near the extracellular surface. It is likely that permeant cations transiently bind to this superficial site, as the first of several steps in passing inward through the channel.     

Zonal heterogeneity of rat hepatocytes in the in vivo uptake of 17 nm colloidal gold granules

The in vivo uptake in hepatocytes of intravenously injected colloidal gold granules with a diameter of 17 nm or 79 nm and coated with bovine serum albumin or with polyvinyl-pyrrolidone was studied. Irrespective of coating only the 17 nm granules were taken up in hepatocytes. Perivenous hepatocytes did take up much more gold granules than periportal hepatocytes. The gold granules were found in lysosomes around bile canaliculi. Two hours after injection hepatocytes contained the maximal amount of granules. At least a portion of the granules was discharged into the bile. The observed zonal gradient in the uptake of 17 nm gold granules might be caused by the greater supply of granules to the perivenous hepatocytes as a combined result of the higher porosity of the endothelial lining and the smaller number of Kupffer cells with a low endocytic activity in this zone.     

Deoxyribonucleic acid homologies among 96 strains of ammonia-oxidizing bacteria

DNA of 96 strains of the genera Nitrosomonas, Nitrosococcus, Nitrosospira, Nitrosolobus, and Nitrosovibrio was isolated and analysed spectrophotometrically. Percentages of guanine plus cytosine (G+C) content, genome sizes, and DNA-DNA homologies were determined. The results indicated the presence of eight Nitrosomonas species, three or four Nitrosococcus species, five Nitrosospira species, and two species of both Nitrosolobus and Nitrosovibrio. DNA homologies between strains of a separate species ranged from 56–100%. Average homologies between strains of different species were 33% in Nitrosococcus, 36% in Nitrosomonas, 37% in Nitrosolobus, 40% in Nitrosospira, and 42% in Nitrosovibrio. Average homologies between species of different genera were 33% and thus not significantly above the background value of 30% detected between DNA of ammonia-oxidizing bacteria and Escherichia coli. Genome sizes ranged from 1.90–2.74×10⁹ dalton in Nitrosomonas, 2.09–2.37×10⁹ dalton in Nitrosococcus, 1.87–2.15×10⁹ dalton in Nitrosospira, 1.92–2.10×10⁹ dalton in Nitrosolobus, and 1.91–2.15×10⁹ dalton in Nitrosovibrio. Differences in genome sizes were in accordance with DNA homologies.     

Immunohistochemical demonstration of FC receptors in rat tissues using immune complexes as ligand

Summary To demonstrate the presence and localization of Fc receptors, rat liver cryostat sections were incubated with heterologous and autologous immune complexes (ICx) and immunoglobulin (Ig) aggregates. Binding was demonstrated using the immunoperoxidase technique. Autologous and heterologous ICx as well as aggregates from human and rat Ig appeared to bind to the sinusoidal wall. ICx bind in preference to aggregates. Monomeric Ig and aggregated Ig from swine and rabbit did not bind. The results demonstrated that ICx and rat and human Ig aggregates were bound via an Fc receptor. This Fc receptor was still intact in livers from carbontetra chloride and galactosamine treated rats. The receptor could also be demonstrated on spleen macrophages and on kidney interstitial cells. This method turned out to be an useful functional histochemical method to localize Fc receptors and to demonstrate their affinity and species specificity in tissues.