Étude pédologique comparative de l'habitat et de l'environnement d'anacanthotermes ochraceus (Burgmeister)

Summary Anacanthotermes ochraceus (Burgmeister), in the oasis of Béni-Abbès (Sahara) will establish its colonies only in the low eathern garden walls and in the clay and straw walls of the houses, where it can find both the water and the malleable clayed materials it requires.Soil analyses have given information on the physico-chemical characteristics of some of the termitaria and of the surrounding sand-hill.The organic matter in the termitarium comes both from the soil and the excrement of the termite. It is high in carbon and low in nitrogen (C/N=2,5), and its mineralization in the présense of gravitational water may result in a loss of mobilizable elements such as the bases.Both the Ph and the aeration of the termitarium favour the mineralization of nitrogenous waste material by bacterial agency.The distribution of calcium carbonate and the condition in which it occurs are more important than the total amount present on account of the part it plays in the texture and structure of the materials, of which the termitarium is composed.A statistical granulometric study of the sand fraction with the results expressed as polar coordinates enables, in comparison with those obtained by mechanical analysis, the texture of the materials colonised byAnacanthotermes ochraceus (Burgmeister) to be defined.

---

Zusammenfassung In der Oase Béni-Abbés (Sahara) gründen dieAnacanthotermes ochraceus (Burgmeister) ihre Kolonien nur in den Wänden der Gärten und in den Mauern der Wohnungen. Dort finden sie das nötige Wasser und die tonigen Plastikmaterialien.Die Bodenanalysen geben Auskunft über einige der characteristichen physikalischchemischen Eigenschaften der Materialien in der Termitenbauten und in dem benachbartem Erg.Das organische Material in den Termitenbauten stammt einerseits aus dem Boden und andererseits aus den Ausscheidungen der Termiten. Reich an Kohlenstoff und arm an Stickstoff (C/N=2,5) kann seine Mineralisation, in Gegenwart von gravifischem Wasser, einen Verlust von einsatzfähigen Elementen, wie den Laugen, nach sich ziehen.Die Bedingungen des Ph und der Belüftung der Termitenbauten sind günstig für eine Mineralisation der stikstoffhaltigen Abfallstoffe auf bakteriellem Wege.Die Verteilung und die Beschaffenheit des CO₃Ca sind dort wichtiger als ihre Gesamtauswertung. Der Grund dafür ist die Rolle, die sie auf der Ebene der Textur und des Aufbaus der Materialen in den Termitenbauten spielen.Die Untersuchung der sandigen Bruchstücke durch die granulometrischen Statistiken in Polarkoordinaten, verglichen mit den Ergebnissen der granulometrischen Analyse, erlauben eine Erklärung der Textur der mit Beschlag belegten kolonisierten Materialen durch dieAnacanthotermes ochraceus (Burgmeister).

     

Morphological and metabolic characterization of a new species of strictly anaerobic rumen fungus: Neocallimastix joyonii

A new strain of strictly anaerobic fungi was isolated from the rumen of sheep. This strain is characterized by a polycentric thallus, an extensive and polynuclear rhizomycelium, polyflagellated zoospores with gamma particle-like bodies. We propose to assign this strain in a new species: Neocallimastix joyonii.     

Effects of abscisic acid on somatic embryo maturation of hybrid larch

Somatic embryos of hybrid larch (Larixleptoeuropaea) whichhad been matured for 4 weeks on maturation medium, developednormally on medium supplemented with 60 µM ABA, but abnormallyon medium with no ABA. A comparative structural and histochemicalinvestigation was carried out on these two types of mature embryos.At the light microscope level, differences between both treatmentswere visible only after 2–3 weeks of maturation. At aroundthis time, abnormal development becomes evident macroscopically:ABA-minus embryos remain rather stubby as opposed to the morecylindrically shaped ABA-plus embryos. Whereas somatic embryosmatured with ABA consist of densely cytoplasmic cells showinga high rate of cell division, ABA-minus embryos are largelymade up of expanded and highly vacuolate cells, indicating thatgrowth in the latter is mainly due to cell expansion and notdivision. After 4 weeks of maturation, ABA-minus embryos beginto elongate in the hypocotyl region, and precocious germinationwas observed frequently. Again, these morphogenetic events werelargely due to abnormal timing of cell expansion. Histochemically,storage proteins were found only in somatic embryos maturedfor 4 weeks with ABA. This observation is in line with resultsobtained by total protein analysis, yielding significantly lowertotal protein contents in ABA-minus embryos both on a freshweight and a per embryo basis after 4–5 weeks of maturation.Deposition of starch grains mainly in the cortex tissue of thehypocotyl region was observed within 2 weeks of maturation invarying amounts regardless of ABA supply. Polyphenols, in particularcatechins and proanthocyanidins, were present in all embryosfrom the very onset of development. They were localized preferentiallyin the proximal suspensor cells and the basal region of theembryo. However, accumulation of polyphenols was generally muchmore pronounced in embryos matured without ABA, indicating alack of biochemical regulatory competence in those embryos. Key words: Abscisic acid, embryonal development, somatic embryo, storage protein, polyphenols     

Regeneration of fertile transgenic indica (group 1) rice plants following microprojectile transformation of embryogenic suspension culture cells

Regenerable embryogenic suspensions of elite Indica (group 1) rice varieties IR24, IR64, IR72 and an advanced Indica rice breeding line IR57311-95-2-3 were established within 6–8 weeks from 3–4 week old calli derived from mature seeds. Transgenic rice plants were obtained by introducing a plasmid carrying genes encoding hygromycin phosphotransferase (hph, conferring resistance to hygromycin B) and ß-glucuronidase (uidA), both driven by the CaMV 35S promoter, via particle bombardment of embryogenic suspensions. The effect of osmotic conditioning on transformation was evaluated. Regenerated plants were resistant to hygromycin B and expressed the uidA (GUS) gene. The growth of mother plants (R₀) was normal and seeds were produced. Southern blot analysis of R₀ and R₁ plants showed that hygromycin resistant plants contained intact hph genes that were inherited in a Mendelian fashion. A protocol for a simple, efficient, repeatable, genotype- and environment-independent Indica rice transformation system is described.Abbreviations 2,4-D 2,4-dichlorophenoxy acetic acid - NAA -naphthalene acetic acid - kb kilobase - GUS ß-glucuronidase - hph hygromycin B phosphotransferase     

Starvation-Induced Stress Resistance in Lactococcus lactis subsp. lactis IL1403

Carbohydrate-starved cultures of Lactococcus lactis subsp. lactis IL1403 showed enhanced resistance to heat, ethanol, acid, osmotic, and oxidative stresses. This cross-protection seems to be established progressively during the transitional growth phase, with maximum resistance occurring when cells enter the stationary phase. Chloramphenicol or rifamycin treatment does not abolish the development of a tolerant cell state but, on the contrary, seems to provoke this response in L. lactis subsp. lactis.     

Cytogenetic analysis of chromosome 5 from the Mediterranean fruit fly,Ceratitis capitata

A cytogenetic map of chromosome 5 from the Mediterranean fruit fly, Ceratitis capitata, was constructed. Six mutations were located by translocation, transposition or deletion mapping. This knowledge allowed alignment and orientation of the existing linkage map with the polytene chromosomes. In addition, mapping of mutations used as selectable markers in genetic sex-separation strains is an essential prerequisite for the improvement of genetic stability during mass-rearing.     

Influence of exogenous abscisic acid on germination and plantlet conversion frequencies of hybrid larch somatic embryos (Larix × leptoeuropaea)

The effect of exogenous abscisic acid, provided to somatic embryos during the maturation step, on endogenous abscisic acid and its main conjugated form (abscisic acid glucose ester), germination and conversion frequencies is presented in this paper. Abscisic acid measurements were obtained after a methanolic extraction, a fractionation through high performance liquid chromatography, quantitation with an immunoassay and identification of the quantitated compound using gas chromatography-mass spectrometry. Results show that endogenous abscisic acid and abscisic acid glucose ester levels are clearly correlated with the exogenous abscisic acid concentration provided to the embryos. Maturation was clearly enhanced by exogenous abscisic acid, but no correlation was found between abscisic acid concentration and germination frequency. Conversely, development of the aerial part of the germinated somatic embryos was dependent upon the abscisic acid concentration in the culture medium and results suggest that this dependence could be related to the endogenous abscisic acid content.     

Changes in carbon storage in temperate humic loamy soils after forest clearing and continuous corn cropping in France

Soil samples from forest and agricultural sites in three areas of southwest France were collected to determine the effect of forest conversion to continuous intensive corn cropping with no organic matter management on soil organic carbon (C) content. Soils were humic loamy soils and site characteristics that may affect soil C were as uniform as possible (slope, elevation, texture, soil type, vegetation). Three areas were selected, with adjacent sites of various ages of cultivation (3 to 35 yr), and paired control forest sites. The ploughed horizon (0-Dt cm) and the Dt-50 cm layer were collected at each agricultural site. In forest sites, each 10 cm layer was collected systematically down to 1 meter depth. Carbon concentrations were converted to total content to a given depth as the product of concentration, depth of sample and bulk density, and expressed in units of kg m^-2. For each site and each sampled layer, the mineral mass of soil was calculated, in order to base comparisons on the same soil mass rather than the same depth. The pattern of C accumulation in forest soils showed an exponential decrease with depth. Results suggested that soil organic carbon declined rapidly during the first years of cultivation, and at a slower rate thereafter. This pattern of decrease can be fitted by a bi-exponential model assuming that initial soil organic carbon can be separated into two parts, a very labile pool reduced during the first rapid decline and more refractory fractions oxidizing at a slower rate. Sampling to shallow depths (0-Dt cm) resulted in over-estimation of the rate of carbon release in proportion to the initial amount of C, and in under-estimation of the total loss of C with age. The results for the 0–50 cm horizon indicated that losses of total carbon average about 50% in these soils, ranging in initial carbon content from 19 to 32.5 kg m^-2. Carbon release to the atmosphere averaged 0.8 kg m^-2 yr^-1 to 50 cm depth during the first 10 years of cultivation. The results demonstrate that temperate soils may also be an important source of atmospheric carbon, when they are initially high in carbon content and then cultivated intensively with no organic matter management.