Flavonoid-like compounds from seeds of red alder (Alnus rubra) influence host nodulation by Frankia (Actinomycetales)

Nitrogen-fixing root nodules are formed by Frankia spp. (Actinomycetales) on dicotyledonous hosts such as alders ( Alnus spp.). Flavonoid-containing preparations from seed washes of red alder ( Alnus rubra Bong.), and individual compounds isolated from such preparations, influenced nodulation of A. rubra by Frankia. Nodulation was enhanced by one flavonoid-like compound, and apparently inhibited by two other such compounds. Four flavonoid-like compounds had no significant effect on nodulation. The seven individual compounds purified from the seed washes were characterized spectrally as possible flavanones and isoflavones. Both the enhancer and the inhibitors appeared to be possible flavanones.     

Optimizing methyl‐eugenol aromatherapy to maximize posttreatment effects to enhance mating competitiveness of male Bactrocera carambolae (Diptera: Tephritidae)

Methyl‐eugenol (ME) (1,2‐dimethoxy‐4‐(2‐propenyl)benzene), a natural phytochemical, did enhance male Bactrocera carambolae Drew & Hancock (Diptera: Tephritidae) mating competitiveness 3 d after ingestion. Enhanced male mating competitiveness can significantly increase the effectiveness of the sterile insect technique (SIT). ME application to mass reared sterile flies by feeding is infeasible. ME application by aromatherapy however, would be a very practical way of ME application in fly emergence and release facilities. This approach was shown to enhance mating competitiveness of B. carambolae 3 d posttreatment (DPT). Despite this added benefit, every additional day of delaying release will reduce sterile fly quality and will add cost to SIT application. The present study was planned to assess the effects of ME‐aromatherapy on male B. carambolae mating competitiveness 1DPT and 2DPT. ME aromatherapy 1DPT or 2DPT did enhance mating competitiveness of B. carambolae males whereas ME feeding 1DPT and 2DPT did not. Male mating competitiveness was enhanced by the ME aromatherapy irrespective if they received 1DPT, 2DPT or 3DPT. ME aromatherapy, being a viable approach for its application, did enhance mating competitiveness of male B. carambolae 1 d posttreatment as ME feeding did 3 d after ingestion.     

Metabolomic profiling of wild‐type and mutant soybean root nodules using laser‐ablation electrospray ionization mass spectrometry reveals altered metabolism

The establishment of the nitrogen‐fixing symbiosis between soybean and Bradyrhizobium japonicum is a complex process. To document the changes in plant metabolism as a result of symbiosis, we utilized laser ablation electrospray ionization‐mass spectrometry (LAESI‐MS) for in situ metabolic profiling of wild‐type nodules, nodules infected with a B. japonicum nifH mutant unable to fix nitrogen, nodules doubly infected by both strains, and nodules formed on plants mutated in the stearoyl‐acyl carrier protein desaturase (sacpd‐c) gene, which were previously shown to have an altered nodule ultrastructure. The results showed that the relative abundance of fatty acids, purines, and lipids was significantly changed in response to the symbiosis. The nifH mutant nodules had elevated levels of jasmonic acid, correlating with signs of nitrogen deprivation. Nodules resulting from the mixed inoculant displayed similar, overlapping metabolic distributions within the sectors of effective (fix⁺) and ineffective (nifH mutant, fix^?) endosymbionts. These data are inconsistent with the notion that plant sanctioning is cell autonomous. Nodules lacking sacpd‐c displayed an elevation of soyasaponins and organic acids in the central necrotic regions. The present study demonstrates the utility of LAESI‐MS for high‐throughput screening of plant phenotypes. Overall, nodules disrupted in the symbiosis were elevated in metabolites related to plant defense.     

A new subfamily of bacterial ABC-type transport systems catalyzing export of drugs and carbohydrates.

Sequence comparison studies revealed that the drug resistance transporter of Streptomyces peucetius (DrrAB) and two nodulation gene products (NodIJ) of Rhizobium leguminosarum are homologous to proteins encoded by three sets of genes that comprise capsular polysaccharide export systems in gram-negative bacteria: KpsTM of Escherichia coli, BexABC of Haemophilus influenzae, and CtrDCB of Neisseria meningitidis. These five systems comprise a new subfamily within the family of ATP binding cassette (ABC)-type transporters. We have termed this subfamily the ABC-2 subfamily. For three of the systems comprising this subfamily (Drr, Nod, and Kps) only one integral membrane constituent has been identified, whereas for the other two systems (Bex and Ctr) two dis-similar integral membrane constituents have been found. This observation suggests that the transmembrane channels of ABC-2-type transporters can be formed of homo- or heterooligomers as is true of several other classes of transport systems.     

The ethylene-inhibitor aminoethoxyvinylglycine restores normal nodulation by Rhizobium leguminosarum biovar. viciae on Vicia sativa subsp. nigra by suppressing the ‘Thick and short roots’ phenotype

Nodulation of Vicia sativa subsp. nigra L. by Rhizobium bacteria is coupled to the development of thick and short roots (Tsr). This root phenotype as well as root-hair induction (Hai) and root-hair deformation (Had) are caused by a factor(s) produced by the bacteria in response to plant flavonoids. When very low inoculum concentrations (0.5–5 bacteria·ml^-1) were used, V. sativa plants did not develop the Tsr phenotype and became nodulated earlier than plants with Tsr roots. Furthermore, the nodules of these plants were located on the primary root in contrast to nodules on Tsr roots, which were all located at sites of lateral-root emergence. The average numbers of nodules per plant were not significantly different for these two types of nodulation. Root-growth inhibition and Hai, but not Had, could be mimicked by ethephon, and inhibited by aminoethoxyvinylglycine (AVG). Addition of AVG to co-cultures of Vicia sativa and the standard inoculum concentration of 5·10⁵ bacteria·ml^-1 suppressed the development of the Tsr phenotype and restored nodulation to the pattern that was observed with very low concentrations of bacteria (0.5–5 bacteria·ml^-1). The delay in nodulation on Tsr roots appeared to be caused by the fact that nodule meristems did not develop on the primary root, but only on the emerging laterals. The relationship between Tsr, Hai, Had, and nodulation is discussed.Abbreviations AVG aminoethoxyvinylglycine - cfu colonyforming units - Had root-hair deformation - Hai root-hair induction - NB naringenin-bacteria filtrate - Tsr Thick and short roots