Plants interact with microbial polysaccharides

Plants are resistant to almost all of the microorganisms with which they come in contact. In response to invasion by a fungus, bacterium, or a virus, many plants produce low molecular weight compounds, phytoalexins, which inhibit the growth of microorganisms. Phytoalexins are produced whether or not the invading microorganism is a pathogen. The production of phytoalexins appears to be a widespread mechanism by which plants attempt to defend themselves against pests. Molecules of microbial origin which trigger phytoalexin accumulation in plants are called elicitors. Structural polysaccharides from the mycelial walls of several fungi elicit phytoalexin accumlation in plants. Approximately 10 ng of the polysaccharide elicits the accumulation in plants of more than sufficient amounts of phytoalexin to stop the growth of microorganisms in vitro. The best characterized elicitors have been demonstrated to be β-1,3-glucans with branches to the 6 position of some of the glucosyl residues. Oligosaccharides, produced by partial acid hydrolysis of the mycelial wall glucans, are exceptionally active elicitors. The smallest oligosaccharide which is still an effective elicitor is composed of about 8 sugar residues. Bacteria also elicit phytoalexin accumulation in plants, but the Rhizobium symbionts of legumes presumably have a mechanism which allows them to avoid either eliciting phytoalexin accumulation or the effects of the phytoalexins if they are accumulated. The lectins of legumes bind to the lipopolysaccharides of their symbiont, but not of their non-symbiont, Rhizobium. It is not known whether the lectin-lipopolysaccharide interaction is involved with the establishment of symbiosis. However, evidence will be presented that suggests that lectins are, in fact, enzymes capable of modifying the structurs of the lipopolysaccharides of their symbiont, but not of their non-symbiont, Rhizobium. It will also be shown that the lipopolysaccharides isolated from different Rhizobium species and from different strains of individual Rhizobium species have different sugar compositions. Thus, the different strains of a single Rhizobium species are as different from one another as the different species of Salmonella and other gram-negative bacteria. This conclusion is substantiated by experiments demonstrating that antibodies to the lipopolysaccharide from a single Rhizobium strain can differentiate that strain from other strains of the same species as well as from other Rhizobium species. The role in symbiosis of the strain-specific O-antigens is unknown.     

A radioimmunoassay for lithocholic acid conjugates in human serum and liver tissue

A sensitive and specific radioimmunoassay for glycine and taurine conjugates of lithocholic acid (CLCA) has been developed. ³H-glycolithocholic acid (S.A. = 17Ci/mmol) was used as tracer. Separation of free from antibody-bound bile acid was carried out using ammonium sulphate (saturated solution). The antiserum showed high specificity for both glyco and tauro conjugated lithocholate (100% cross reaction) and lithocholic acid (25% cross reaction). The sensitivity of the assay (1 pmole/tube), was adequate for measuring CLCA in peripheral blood and hepatic tissue in man.     

Cytologic evidence for three human X-chromosomal segments escaping inactivation

Summary Early replication of prometaphasic human sex chromosomes was studied with the bromodeoxyuridine (BrdU)-replication technique. The studies reveal that two distal segments of Xp, including bands Xp 22.13 and Xp 22.3, replicate early in S-phase and therefore may not be subject to random inactivation. Furthermore, the replication of these distal segments of Xp occurs synchronously with those of the short arm of the Y chromosome including bands Yp 11.2 and Yp 11.32. These segments of Xp and Yp correspond well to the pairing segment of the X and Y chromosomes where a synaptonemal complex forms at early pachytene of human spermatogenesis. The homologous early replication of Yp and the distal portion of Xp may be interpreted as a remnant left untouched by the differentiation of heteromorphic sex chromosomes from originally homomorphic autosomes. A third early replicating segment is situated on the long arm of the X chromosome and corresponds to band Xq 13.1. This segment may be correlated with the X-inactivation center postulated by Therman et al. (1979).     

Effect of canine surfactant protein (SP-A) on the respiratory burst of phagocytic cells

Cells obtained from bronchoalveolar lavage, or neutrophils of peripheral blood of dog, were incubated with the canine surfactant-associated protein A (SP-A). A significant decrease of the production of Superoxide anion was observed after subsequent stimulation with phorbol-12-myristate-13-acetate (PMA) as measured by the lucigenin-dependent chemiluminesence (CL). Several other proteins used for control experiments did not decrease lucigenin-dependent CL, indicating a specific effect of SP-A on phagocytes. Treatment of SP-A with collagenase prior to incubation with neutrophils destroyed the depleting effect on oxygen radical production of PMA-stimulated cells. We propose that SP-A acts as a regulatory factor of the respitatory burst of alveolar macrophages and neutrophils in the lungs. The inhibitory effect of SP-A is down-regulated by collagenase released from stimulated alveolar macrophages.     

Nonspecific X-linked mental retardation—A review

Summary Mental retardation, in particular the X-linked type, has interested geneticists for many years. An increasing number of affected families have been to genetic counselling centres, and an effort is being made to find clinical and cytogenetic methods so a reliable diagnosis can be made. This would enable the detection of carriers and the opportunity to offer prenatal diagnosis. Many questions remain regarding X-linked mental retardation, its causes, diagnosis, and prevention. In this article we try to give an overview about the status of our present knowledge and the questions to be answered in the future.     

Potentiation of arginine-induced glucagon secretion by adenosine

Adenosine and the synthetic adenosine agonists 2-chloroadenosine and N⁶-(L-2-phenylisopropyl)-adenosine were tested for effects on hormone secretion from the rat isolated perfused pancreas. These nucleosides, at concentrations of 5 μM, markedly potentiated both phases of arginine-induced glucagon release; the two synthetic agonists were more effective than adenosine. In the absence of arginine, each of the nucleosides induced a transient burst of glucagon. In contrast, adenosine and both synthetic agonists inhibited arginine-induced insulin secretion to varying degrees and caused only negligible insulin release when perfused without arginine. The adenosine antagonist 8-($\text{p}$-sulfophenyl)-theophylline prevented the actions of adenosine on hormone release from the pancreas. Our data suggest that adenosine potentiation of arginine-induced glucagon release may be mediated via adenosine receptors on alpha cell membranes; such a mechanism could provide an important endogenous control over glucagon secretion.     

Structural regularities in tetraether lipids of Caldariella and their biosynthetic and phyletic implications

Individual di(biphytanyl) diglycerol tetraether lipids from thermoacidophile archaebacteria of the Caldariella series, with differently cyclized biphytanyl components, are separated and shown to have structures 8–12, with the glycerol and biphytanyl components demonstrably both antiparallel and with partial assignments of stereochemistry. Tetraethers with alternative arrangements of the components are absent. The structures allow previous observations on these and related lipids to be rationalized both biosynthetically and phyletically.