A biovar-specific signal of Rhizobium leguminosarum bv. viciae induces increased nodulation gene-inducing activity in root exudate of Vicia staiva subsp. nigra

Microbial Biotechnolog

Competitiveness and communication for effective inoculation byRhizobium, Bradyrhizobium and vesicular-arbuscular mycorrhiza fungi

After a short summary on the ecology and rhizosphere biology of symbiotic bacteria and vesicular-arbuscular (VA) mycorrhiza fungi and their application as microbial inocula, results on competitiveness and communication are summarized. Stress factors such as high temperature, low soil pH, aluminium concentrations and phytoalexins produced by the host plants were studied withRhizobium leguminosarum bv.phaseoli andRhizobium tropici onPhaseolus beans. Quantitative data for competitiveness were obtained by usinggus + (glucoronidase) labelled strains, which produce blue-coloured nodules. ForPhaseolus-nodulating rhizobia, a group specific DNA probe was also developed, which did not hybridize with more than 20 other common soil and rhizosphere bacteria. Results from several laboratories contributing to knowledge of signal exchange and communication in theRhizobium/Bradyrhizobium legume system are summarized in a new scheme, including also defense reactions at the early stages of legume nodule initiation. Stimulating effects of flavonoids on germination and growth of VA mycorrhiza fungi were also found. A constitutive antifungal compound in pea roots, -isoxazolinonyl-alanine, was characterized

Solanum tuberosurn mRNA for pectin methylesterase 2

EMBL datasubmission X9776

Solanurn tuberosurn mRNA for pectin methylesterase 1

EMBL data submission X9776

Solanum tuberosurn mRNA for pectin methylesterase 2

EMBL datasubmission X9776

The uncoupling efficiency and affinity of flavonoids for vesicles

The relative hydrophobicity and interaction of flavonoids with artificial membranes using vesicles was studied. At the same degree of hydroxylation, flavones were slightly more hydrophobic than flavanones. Flavonoids possess a hydrophobic character and are weak acids. For this reason, their uncoupling efficiency of the membrane potential was studied using cytochrome c oxidase vesicles. With emphasis on naringenin, it was shown that flavonoids affect both the transmembrane potential difference (V) and the transmembrane pH difference (V). Flavones were slightly more effective in uncoupling the membrane potential than flavanones; the 7OH group seems to play an important role. Hydroxylation of the exocyclic phenyl group decreased the uncoupling efficiency for all flavonoids studied. The flavonol quercitin exhibited hardly any uncoupling activity. Glycosylation abolished all uncoupling activity. The affinity of flavonoids for vesicle membranes was also studied using the fluorescence quenching of the membrane probe diphenylhexatriene. Flavonols exhibited a substantially higher affinity for liposomes than flavanones. This difference in affinity is assumed to be caused by the far more planar configuration of the flavonols in comparison with the tilted configuration of flavanones. Due to this planar configuration, it seems reasonable to assume that flavonols could more easily intercalate into the organised structures of the phospholipids within the vesicle membranes than flavanones. It is concluded that, in vivo, hardly any uncoupling activity of flavonoids can be anticipated. However, the quercitin plasma concentration in vivo can be such that, based on the affinity study, part of this flavonol could be associated with biological membranes to function there as, for example, an antioxidant