Variation in N2 fixation,N and P contents of mycorrhizalVigna unguiculata in relation to the progressive development of extraradical hyphae ofGlomus mosseae

Summary Vigna unguiculata cv. 58–185 grown in a sterile Dek soil was inoculated withRhizobium sp. orRhizobium sp. plusGlomus mosseae. Response of the host plant to the treatments was estimated by periodic measurements of shoot and nodule dry weights, N₂ fixation (C₂H₂ reduction activity) and N and P contents up to the 50th day of the growth cycle. It was only 45 days after planting that shoot dry weight of dually inoculated plants differed significantly from that of plants inoculated withRhizobium sp. alone. Nodule dry weight and N₂ fixation of dually inoculated plants were significantly higher than those of plants inoculated withRhizobium sp. alone from day 20 after planting, but there was no significant difference in N content (%). During the first 20 days, shoot P content (%) of both sets of plants decreased progressively, P content of dually inoculated plants being lower than that of the others. Later, P content of dually inoculated plants increased rapidly whereas P content of the other plants remained constant. Increase in nodule dry weight, N₂ fixation and P content of dually inoculated plants corresponded to the onset of the development of the extra-radical hyphae ofGlomus mosseae. In the rhizosphere.

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Resumen Se cultivóVigna unguiculata cv. 58–185 en un suelo estéril tipo Dek, se inoculó conRhizobium sp. o conRhizobium sp. másGlomus mosseae. La respuesta de la planta huésped a los tratamientos se estudió midiendo periodicamente el peso seco de la parte aerea y de los nódulos, la fijación de N (actividad reductora de C₂H₂) y los contenidos de N y P hasta el 50° día del ciclo de crecimiento. La diferencia entre el peso seco de la parte aerea de las plantas con doble inoculación y aquellas inoculadas conRhizobium sp. unicamente, no fue significativa hasta 45 días despúés de la siembra. A los 20 días de la siembra tanto el peso seco de los nódulos como la fijación de nitrógeno de las plantas con doble inoculación eran significativamente superiores a los valores obtenidos para las plantas con soloRhizobium sp., aunque no se observaron diferencias en el contenido en N (%). Durante los primeros 20 días del ciclo el contenido en P (%) de ambos grupos de plantas disminuyó progresivamente, siendo los valores obtenidos por las plantas con doble inoculación inferiores a los de las demás. Más tarde el contenido en P de las plantas con doble inoculación aumentó rapidamente manteniéndose constante el de las demás. El incremento en el peso seco de los nódulos, en la fijación de N y en el contenido en P de las plantas con doble inoculación se correspondió con el inicio del desarrollo de las hifas extraradiculares deGlomus mosseae.

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Résumé On a inoculéV. unguiculata poussant dans un sol Dek stérile avecRhizobium etRhizobium plusGlomus mosseae. On a recherché la réponse de la plante-hôte à ces deux traitements en estimant périodiquement les poids des nodules et des parties aériennes de la plante, la fixation d'azote (activité réductrice de C₂H₂), les teneurs en N et P jusqu'au 50^e jour du cycle de végétation. C'est seulement au 45^e jour après la plantation que le poids sec des parties aériennes des plantes inoculées avec deux symbiotes (plantes doublement inoculées) diffère significativement de celui des plantes inoculées avec Rhizobium seul. Le poids sec des nodules et la fixation N₂ des plantes doublement inoculées sont significativement plus élevés que ceux des plantes inoculées avecRhizobium seul au 20^e jour après la plantation mais il n'y a pas de différence significative pour la teneur en N (%). Pendant les 20 premiers jours, la teneur en P (%) des parties aériennes des deux catégories de plantes décroit progressivement; la teneur en P des plantes doublement inoculées est plus faible que celle des plantes inoculées seulement avecRhizobium. Plus tard, la teneur en P des plantes doublement inoculées augmente rapidement tandis que celle des autres plantes reste constante. L'accroissement du poids sec des nodules, de la fixation d'azote et de la teneur en P observé chez les plantes doublement inoculées correspond au démarrage du développement des hyphes extra-radicales deGlomus mosseae dans la rhizosphère.

     

IR vibrational CD in model deoxyoligonucleotides: observation of the B----Z phase transition and extended coupled oscillator intensity calculations

The first observation of ir vibrational CD (VCD) in small model DNA molecules is reported. The VCD signals in the 1550-1750-cm-1 spectral region, which originate from coupling of carbonyl stretching modes of the nucleic acid bases, are found to be sensitive to the handedness of the polymer helix. The formalism to calculate VCD intensities of polymers is developed from the exciton model derived earlier by Tinoco [(1963) Radiation Res. 20, 133; (1960) J. Chem. Phys. 33, 1332; (1964) J. Am. Chem. Soc. 86, 297] and Schellman and co-workers [(1975) Biopolymers 14, 173; (1969) J. Phys. Chem. 73, 28]. The resulting equations, which are a direct extension of the dimeric case known as the "coupled oscillator," are used in model calculations of the helical polymers.     

Differential DNA binding of nuclear proteins to a long terminal repeat region of the MCF13 and Akv murine leukemia viruses.

Long terminal repeat (LTR) sequences of murine leukemia viruses (MLVs) have been demonstrated to be mainly responsible for the pathogenic differences in these retroviruses. A region of the LTR which is downstream of the enhancer elements has been shown to contribute both to enhancer activity as well as to disease specificity of MLVs. We have identified protein-DNA complexes generated by this region of a lymphomagenic MLV (MCF13) and one which is nonpathogenic (Akv). One protein-DNA complex we have observed for this region is unique to MCF13 DNA sequences. Detection of protein involved in this unique MCF13 complex in different cell lines revealed that it was ubiquitous.     

Selection of Bradyrhizobium strains and provenances of Acacia mangium and Faidherbia albida: Relationship with their tolerance to acidity and aluminium

This work was designed to determine the role of the acidity and aluminium stress in the selection of partners in the Acacia symbioses with relevance to the persistence of the microsymbiont Bradyrhizobium in the soil and the growth and nodulation of the host plant respectively. Fifteen strains of Bradyrhizobium from Acacia mangium and Faidherbia albida formed a very homogenous acid tolerant group as indicated by their ability to grow better in a medium at pH 4.5 than in a medium at pH 6.8. By contrast, a growth experiment using an acid liquid media (pH 4.5), containing different concentrations of aluminium successfully identified strains sensitive to aluminium toxicity and those able to grow even in the presence of 100 M AlCl₃.Our results suggest that high amounts of aluminium in the soil rather than acidity (pH 4.5) were a major soil factor for selection of Bradyrhizobium strains capable of establishing a permanently high population under natural conditions.Unlike the behaviour of the microsymbiont, growth and nodulation of Acacia mangium and Faidherbia albida were not affected by aluminium, even at 100 M, but they might be significantly affected by medium acidity (pH 4.5) depending on plant provenances. It is therefore suggested that ability of the host plant to tolerate acidity stress should be taken into account first when screening effective Acacia-Bradyrhizobium combinations for use in afforestation trials.     

Strategies for the computation of infrared CD and absorption spectra of biological molecules: ribonucleic acids.

We report observed and computed infrared (vibrational) circular dichroism spectra of a number of polyribonucleic acids in aqueous solutions in the 1600-1750 cm-1 spectral region, in which C = O and some nucleotide base ring stretching vibrations occur. The experimental data are compared with results calculated using different levels of sophistication within the exciton approach. We find that observed band shapes are generally well reproduced by these models, particularly if care is taken to determine the direction of the vibrational dipole transition moments accurately.     

Influence of iron depletion on growth and production of catechol siderophores by different Frankia strains

Nine strains of Frankia isolated from six Casuarinaceae (including four Casuarina sp., one Allocasuarina and one Gymnostoma) and one Elaeagnaceae (Hippophae¨ rhamnoides) were screened for growth and production of siderophores in an iron-deficient liquid medium. Siderophore production was detected only in four strains (Cj, G2, CH and G82) using the CAS and Arnow assays. Salicylates formed more than 90% and dihydroxybenzoates formed less than 10% of all catechol-type siderophores produced. Growth of the former strains was less affected by iron deficiency than that of strains Rif, Thr, URU, BR and RT which do not produce siderophores. Optimal siderophore production by strain Cj was noted when iron concentration reached 0.5μm and was completely inhibited at an iron concentration of 10μm. The kinetics of siderophore production by strain Cj showed that siderophore synthesis was detectable during the growth stationary phase. Growth of Cj (a siderophore-producing strain) and of RT (a non-siderophore-producing strain) differed when 2,2-dipyridyl or ethylene di(o-hydroxyphenyl) acetic acid (EDDHA) was added to the iron-deficient growth medium. Frankia strain RT was the most sensitive to the detrimental effect of both iron chelators.     

Effect of inoculation withGlomus mosseae on nitrogen fixation by field grown soybeans

Summary This field study was undertaken to determine the effect of inoculation withGlomus mosseae on N₂ fixation and P uptake by soybean. The inoculation withGlomus mosseae was achieved using a new type of inoculant, alginate-entrapped (AE) endomycorrhizal fungus. N₂ fixation was assessed using the A value method. In P-fertilized plots, inoculation with AEGlomus mosseae increased the harvest index based on dry weight (+20%) and N content of seeds (+17%), the A value (+31%) and %N derived from fixation (+75%). Inoculation with AEGlomus mosseae decreased the coefficient of variation for the A value and for the dry weights of the different plant parts.     

IR (vibrational) CD of peptide beta-turns: a theoretical and experimental study of cyclo-(-Gly-Pro-Gly-D-Ala-Pro-).

IR vibrational CD (VCD) has been observed for the cyclic pentapeptide cyclo-(-Gly-Pro-Gly-D-Ala-Pro-) in solution in CDBr3. The observed VCD spectra do not resemble the VCD features of any of the previously reported peptide secondary structures, such as alpha-helical, "random coil," or sheet structures, and might be due to the beta-turn contained in this molecule. To shed light onto the origin of the observed spectra, VCD intensity calculations, based on the solution and solid-state structures of cyclo-(-Gly-Pro-Gly-D-Ala-Pro-), have been carried out. In addition, calculated VCD data for pure beta-turns are discussed.     

In Vitro Nitrogen Fixation by Two Actinomycete Strains Isolated from Casuarina Nodules

Acetylene reduction activity was demonstrated in pure cultures of two actinomycete strains isolated from nodules of Casuarina equisetifolia. This activity was comparable to that of free-living Rhizobium strains, but appeared to be less sensitive to pO₂ and more sensitive to the presence of combined nitrogen.     

Cultivation and biomass production of the diatom Thalassiosira weissflogii as a live feed for white-leg shrimp in hatcheries and commercial farms in Vietnam

This study investigated the biomass production process from the laboratory to the pilot scale in order to use the nutrient-rich biomass of the diatom Thalassiosira weissflogii as live feed for white-leg shrimp (Litopenaeus vannamei) at larval stages (zoeal, mysis, and postlarval) and in commercial production in hatcheries in Vietnam. Our results showed that T. weissflogii was successfully cultured in 1–2 L Erlenmeyer flasks, 0.2–3.5 m³ composite tanks, and 6.5 m³ tubular photobioreactors, with the highest cell density of 1.6 × 10⁶ cells mL^?1 reached after 6 days of culture. Under optimal culture conditions, the protein, lipid, and carbohydrate contents in this algal biomass were 13.2%, 20.0%, and 10.0% of dry cell weight, respectively. The fatty acid composition contains high amount of palmitic acid (C16:0, 43.11% of total fatty acid), and polyunsaturated fatty acids (PUFAs), such as eicosapentaenoic acid (EPA, C20:5ω-3), approximated 16.5% of total fatty acid. In a 50 L larval rearing tank, at the optimal stocking density of 125 nauplii L^?1, the survival percentage (75.55%), the total body length (from 5.376 ± 0.007 to 10.860 ± 0.030 mm), and weight (at from PL₁ to PL₁₂ stages) (from 0.145 ± 0.002 to 1.158 ± 0.005 g) of the white-leg shrimp larvae reached the highest values but the metamorphosis time (234 h) was shortest compared with the other stocking densities. Further, adding living T. weissflogii biomass to the diet of white-leg shrimp larvae at the nauplii 6 stage led to an increase in the body length, weight, and survival percentage of white-leg shrimp larvae of 21.17%, 35.7%, and 33% higher compared with those of larvae fed the control diet (without the addition of T. weissflogii), respectively. At the same time, the metamorphosis time of larvae (from Z₁ to PL₁) decreased by 4 h compared to the control group. In intensive ponds (area of 6400 m² pond^?1), using seed stocks at the postlarvae 12 stage that had been fed T. weissflogii, the final weight, yield, and survival percentage of the shrimp were increased by 7.3%, 14.2%, and 16.3%, respectively, compared with those of the control group. There were no statistically significant differences in the protein and carbohydrate contents in the shrimp flesh among the experimental and control group (p > 0.05). The lipid, omega-3, omega-6, and omega-9 fatty acid contents of shrimp flesh in experiment formula (per 100 g shrimp) were 1.21 g, 72.9 mg, 114 mg, and 86.1 mg, 11%, 29%, 21.6%, and 17.7% higher than that those in control, respectively. The obtained results show the great potential of using T. weissflogii as live feed on white-leg shrimp farms in Vietnam.