Showing papers by "Institut national de la recherche agronomique published in 1990"

Correlation between ultrastructural differentiation of bacteroids and nitrogen fixation in alfalfa nodules.

Abstract: Bacteroid differentiation was examined in developing and mature alfalfa nodules elicited by wild-type or Fix- mutant strains of Rhizobium meliloti. Ultrastructural studies of wild-type nodules distinguished five steps in bacteroid differentiation (types 1 to 5), each being restricted to a well-defined histological region of the nodule. Correlative studies between nodule development, bacteroid differentiation, and acetylene reduction showed that nitrogenase activity was always associated with the differentiation of the distal zone III of the nodule. In this region, the invaded cells were filled with heterogeneous type 4 bacteroids, the cytoplasm of which displayed an alternation of areas enriched with ribosomes or with DNA fibrils. Cytological studies of complementary halves of transversally sectioned mature nodules confirmed that type 4 bacteroids were always observed in the half of the nodule expressing nitrogenase activity, while the presence of type 5 bacteroids could never be correlated with acetylene reduction. Bacteria with a transposon Tn5 insertion in pSym fix genes elicited the development of Fix- nodules in which bacteroids could not develop into the last two ultrastructural types. The use of mutant strains deleted of DNA fragments bearing functional reiterated pSym fix genes and complemented with recombinant plasmids, each carrying one of these fragments, strengthened the correlation between the occurrence of type 4 bacteroids and acetylene reduction. A new nomenclature is proposed to distinguish the histological areas in alfalfa nodules which account for and are correlated with the multiple stages of bacteroid development.

Exocellular polysaccharides produced by lactic acid bacteria.

Abstract: The production of homopolysaccharides (dextrans, mutans) and heteropolysaccharides by lactic acid bacteria, their chemical composition, their structure and their synthesis are outlined. Mutans streptococci, which include Streptococcus mutans and S. sobrinus produce soluble and insoluble α-glucans. The latter may contain as much as 90%α-1–3 linkages and possess a marked ability to promote adherence to the smooth tooth surface causing dental plaque. Dextrans produced by Leuconostoc mesenteroides are high molecular weight α-glucans having 1–6, 1–4 and 1–3 linkages, varying from slightly to highly branched; 1–6 linkages are predominant. Emphasis is put on exopolysaccharide producing thermophilic and mesophilic lactic acid bacteria, which are important in the dairy industry. The produced polymers play a key role in the rheological behaviour and the texture of fermented milks. One of the main problems in this field is the transitory nature of the thickening trait. This instability is not yet completely understood. Controversial results exist on the sugar composition of the slime produced, but galactose and glucose have always been identified with galactose predominating in most cases.

Medicago truncatula, a model plant for studying the molecular genetics of the Rhizobium-legume symbiosis.

Abstract: Medicago truncatula has all the characteristics required for a concerted analysis of nitrogen-fixing symbiosis withRhizobium using the tools of molecular biology, cellular biology and genetics.M. truncatula is a diploid and autogamous plant has a relatively small genome, and preliminary molecular analysis suggests that allelic heterozygosity is minimal compared with the cross-fertilising tetraploid alfalfa (Medicago sativa). TheM. truncatula cultivar Jemalong is nodulated by theRhizobium meliloti strain 2011, which has already served to define many of the bacterial genes involved in symbiosis with alfalfa. A genotype of Jemalong has been identified which can be regenerated after transformation byAgrobacterium, thus allowing the analysis ofin-vitro-modified genes in an homologous transgenic system. Finally, by virtue of the diploid, self-fertilising and genetically homogeneous character ofM. truncatula, it should be relatively straightforward to screen for recessive mutations in symbiotic genes, to carry out genetic analysis, and to construct an RFLP map for this plant.

Xylem dysfunction in Quercus: vessel sizes, tyloses, cavitation and seasonal changes in embolism

Abstract: Summary The seasonal progression of xylem dysfunction from tyloses and embolism induced both by cavitation and frost was studied in Quercus rubra L. and Quercus alba L. branches. Vessel lengths and diameters were measured in current-year rings of branches of various ages. Vessels in current-year shoots are about the same size as those in many diffuse porous trees, but vessels in older branches are two to six times larger in diameter and typically more than 10 times longer. Large Quercus vessels were more vulnerable to cavitation than small vessels. The small vessels in current-year shoots were more vulnerable to cavitation than vessels of comparable size in diffuse porous species. Earlywood vessels are completely blocked by tyloses within a year of their formation. Tylose growth starts in winter, but the vessels are not fully blocked until the next summer. Many latewood vessels, by contrast, remain free of complete blockage for several years. In Q. rubra, loss of hydraulic conductivity in current-year shoots due to cavitation reaches 20% by August and > 90% after the first hard frost. Both laboratory and field observations confirm that the role of frost in causing loss of hydraulic conduction by embolism is much more dramatic in Quercus than in conifers and diffuse porous hardwoods.

A comparison of kriging, cubic splines and classification for predicting soil properties from sample information

Abstract: SUMMARY The clay content of the topsoil in two regions of contrasting physiography was predicted from sample data using four different procedures. The predictors were the means of mapped classes, the usual kriging estimator, a cubic spline interpolator and a kriging estimator within classes using a pooled within-class variogram. The performances of the procedures were evaluated and compared. In the first region, Sandford St Martin on Jurassic sediments where there were some abrupt changes in soil, the classification predicted best within those classes bounded by sharp change. Elsewhere the usual kriging performed somewhat better, and kriging within classes was still more precise. In the second region, Yenne on the alluvial plain of the Rhone where the soil varied gradually, kriging performed better than classification, though a small improvement resulted from combining kriging with classification. Both prediction by class means and kriging attempt to minimize the estimation variance, and their mean prediction variances were close to the theoretical values overall. Spline interpolation is more empirical, and though it followed the abrupt changes better than kriging, it fluctuated excessively elsewhere, and its overall performance was poorer than that of kriging.

The parthenogenetic development of rabbit oocytes after repetitive pulsatile electrical stimulation

Abstract: Freshly ovulated rabbit oocytes were activated parthenogenetically by periodically repeated calcium stimuli generated by electric field pulses applied onto the plasma membrane. Electric field pulses of 1.8 kV cm-1 were delivered every 4 min for 1 h 30 min (22 double pulses) in a specially designed chamber. Before each pulse, the culture medium was replaced by an isotonic glucose solution containing 10 microM Ca2+. The effects of modulating the ionic stimuli (by changing the duration of EF pulse) on a postactivation reaction, and/or on the pre- and postimplantation development, were studied. The rate of activation increased progressively as the pulse duration lengthened. For 22 pulses of 200 microseconds, 13% of oocytes were activated versus 100% for 1200 microseconds. The uniformity of the parthenogenetic response was obtained when oocytes were exposed to a series of pulses within which the reduction of pulse duration followed a negative exponential law. The influence of such activating treatment on the preimplantation development was tested using two treatments of 22 pulses with a total pulse duration equal to 14,868 and 11,228 microseconds, respectively. For the weaker treatment, a lower proportion of embryos underwent compaction and those that compacted were irregular. In contrast, the majority of embryos resulting from the stronger treatment compacted and developed into blastocysts. The most significant result that emerges from this study is that the level of stimulation affects in vitro developmental potency after the third cleavage division. The postimplantation viability of parthenogenetic eggs was tested and the results showed that parthenogenetic rabbit embryos died at a similar stage of development to the parathenogenetic mouse embryos. But, in the present series, high implantation rates and embryonic development (66%) till day 10-11 of pregnancy were obtained after the appropriate pulsatile EF treatment of oocytes. The parthenogenetic fetuses were of smaller size than the controls, but the development of the trophoblast tissue was proportional to the development of the fetuses. Anomalies of fetuses were also observed. This study reveals that activation is not a time-limited event and that the type of activating treatment has a marked effect on the ability of the resulting parthenogenetic embryos to develop to the early postimplantation stages. The sustained alteration of the cytoplasmic activity provides a useful tool to study the function of embryonic or somatic nuclei introduced during the earliest stages of activation.

The estradiol-induced surge of gonadotropin-releasing hormone in the ewe.

Abstract: Previous studies suggest two roles for estradiol in inducing the LH surge in ewes: a neural action to evoke a sudden release of GnRH and a pituitary action to maximize response to GnRH. We tested two hypotheses: a follicular phase estradiol rise induces a GnRH surge; and the surge-inducing action of estradiol does not vary with season. In the breeding season, ewes in the midluteal phase of the estrous cycle were ovariectomized and treated with implants producing luteal phase levels of estradiol and progesterone, and an apparatus was surgically installed for later sampling of pituitary portal blood. At the normal time of luteolysis (1 week later), progesterone implants were removed, simulating luteal regression. Ewes were divided into two groups: estradiol implants also removed (n = 6) and estradiol implants added 16 h after progesterone removal to produce a rise in estradiol to levels that mimic those that circulate in the late follicular phase (n = 6). In anestrus, the estradiol rise treatment was replicated in ewes (n = 5) after an artificial luteal phase produced by sequential insertion and subsequent removal of progesterone implants. Regardless of season, the LH surge induced by estradiol was invariably accompanied by a massive GnRH surge, ranging from 73- to 394-fold over presurge values. The GnRH and LH surges began together, but the GnRH surge continued well beyond the surge of LH. There was no seasonal difference in time course or amplitude of the GnRH surge. Control ewes not treated with estradiol exhibited regular pulses of LH and GnRH every 1-2 h, but no surge of either hormone. We conclude that, regardless of season, a rise in estradiol to late follicular phase levels initiates a large and abrupt GnRH surge coincident with the onset of the LH surge. The LH surge ends despite continued elevation of GnRH.

Effect of tillage on soil organic carbon mineralization estimated from 13C abundance in maize fields

Abstract: SUMMARY Three methods of cultivation, conventional tillage (CT), superficial tillage (ST) and no-tillage (NT), were applied for 17 years to continuous maize. Their effect on soil organic carbon content was investigated through measurements of carbon and 13C/12C ratios, using the natural difference in 13C content between C3 plants and maize, which is a C4 plant. Because the soil had carried C3 plants before the experiment started, the organic carbon remaining from that time (C3,-carbon), was distinguished from the carbon derived from maize. Comparison between continuous wheat and maize plots showed that organic matter from both maize and wheat decomposed without significant 13C enrichment, whereas older C3-carbon was enriched by 1.5% compared to that of fresh wheat material. From the initial 3.6 kg C m−2 in the topsoil (0–30 cm), 0.95 were mineralized in the CT treatment, but only 0.45 in NT. The mineralization was the same in the tilled layer of ST as in CT. The CT treatment accumulated 1.1 kg C m−2 of maize-derived carbon and the NT treatment 0.8. The mineralization of initial C3-carbon was the same at all depths between 0 and 30 cm in the NT treatment; 75% of the carbon derived from maize was found in the 0–5 cm layer.

Assembly of coronavirus spike protein into trimers and its role in epitope expression.

Abstract: The folding and oligomerization of coronavirus spike protein were explored using a panel of monoclonal antibodies. Chemical cross-linking and sedimentation experiments showed that the spike of transmissible gastroenteritis virus is a homotrimer of the S membrane glycoprotein. The spike protein was synthesized as a 175,000-apparent-molecular-weight (175K) monomer subunit that is sensitive to endo-beta-N-acetylglucosaminidase H. Assembly of monomers into a trimeric structure was found to occur on a partially trimmed polypeptide and to be a rate-limiting step, since large amounts of monomers failed to trimerize 1 h after completion of synthesis. Terminal glycosylation of newly assembled trimers, resulting in the biosynthesis of three 220K oligomers, occurred with a half time of approximately 20 min. Monomeric (230K to 240K) processed forms were also observed in cells and in virions. The 175K monomeric form expressed four major antigenic sites previously localized within the amino-terminal half of the S polypeptide chain; however, two classes of trimer-restricted epitopes (borne by three 220K and/or three 175K oligomers) were identified. The S glycoprotein of coronavirus might be a valuable model system for discovering new aspects of the maturation of membrane glycoproteins.

Meat tenderization: possible causes and mechanisms. a review.

Abstract: The postmortem meat tenderizing process is complex and not fully understood. The nature of changes associated with the improvement in tenderness and the exact mechanisms involved are still unknown. Based on relevant evidence, old and new, this review attempts to clarify the statement of our knowledge of these aspects. Of the different biochemical and ultrastructural changes occurring in meat, a key role of myofibril disruption taking place at the N2-line level in meat tenderization has been emphasized. This may be ascribed to the action of lyosomal enzymes, especially cathespin B and L. However, all the changes thus far identified can be only explained by a synergistic action of lysosomal and calcium-dependent proteinases. Besides or together with proteolytic enzymes, weakening of myofibrils may also be mediated by the high ionic strength achieved in postmortem muscles. Both mechanisms possibly involved in the meat tenderizing process have been tentatively tested in relation with the large muscle variability in aging rate. It appears that some concepts are in conflict with the results presented. For instance, no direct relationship was found between aging rate and proteinase content of muscles.

Estimate of organic matter turnover rate in a savanna soil by 13C natural abundance measurements.

Abstract: The medium-term dynamics of organic matter in a sandy savanna soil has been investigated at Lamto (Ivory Coast) through changes in the 13C/12C ratio induced by vegetation changes from the C4 to the C3 photosynthetic pathway. After 25 yr of protection from fire, a soil previously covered by C4 grassland vegetation had been progressively colonized by C3 woody plants. Although the total C content did not show significant changes. 52–70% of the original C4 carbon was turned over when vegetation cover was changed. Turnover of coarse organic debris (> 250 μm) was much greater (97%) than the mineralization (50%) of clay-associated fractions (< 20 μm).

Chemical information processing in the olfactory system of insects.

Abstract: Review about chemical information processing in insects. Integration between behavioral and neurophysiological studies to clarify in more detail the underlying mechanisms in insect olfaction

Energy utilization in pregnant and lactating sows: modeling of energy requirements'

Abstract: Data on energy metabolism and body composition changes of the pregnant and lactating sow have been considered in order to propose methods for determination of energy requirements according to a factorial approach. Daily requirements for maintenance at thermoneutrality amounts to about 105 and 110 kcal ME& BW7’ in pregnant and lactating sows, respectively. During pregnancy, maintenance represents 75 to 85% of the total requirements and is affected greatly by environmental temperature and activity of the animals. Requirements for total uterine gain are low, but they increase with advancement of pregnancy. In addition, the daily ME requirements during pregnancy depend on the amount and composition of maternal weight gain and on the previous lactation body weight loss. The factorial approach indicates clearly that daily ME recommendation in pregnant sows varies from 6 to more than 10 Mcal and must be adapted to each sow within a herd. A method for prediction of ME requirements in lactating sows that considers a relatively precise estimate of energy output in milk is proposed. Results indicate that daily ME requirements are particularly high (15 to more than 20 Mcal) and generally are not met by voluntary feed intake. Emphasis also has been given to prediction of body composition changes that occur over the reproductive life of the sow. Data from the factorial approach allow for optimization of sow energy nutrition to ensure a normal evolution of body weight changes and to avoid major changes in body weight and composition. However, no available data demonstrate whether such a strategy is concomitant with optimal lifetime

Rhizobium meliloti Genes Encoding Catabolism of Trigonelline Are Induced under Symbiotic Conditions

Abstract: Rhizobium meliloti trc genes controlling the catabolism of trigonelline, a plant secondary metabolite often abundant in legumes, are closely linked to nif-nod genes on the symbiotic megaplasmid pSym [Boivin, C., Malpica, C., Rosenberg, C., Denarie, J., Goldman, A., Fleury, V., Maille, M., Message, B., and Tepfer, D. (1989). In Molecular Signals in the Microbe-Plant Symbiotic and Pathogenic Systems. (Berlin: Springer-Verlag), pp. 401-407]. To investigate the role of trigonelline catabolism in the Rhizobium-legume interaction, we studied the regulation of trc gene expression in free-living and in endosymbiotic bacteria using Escherichia coli lacZ as a reporter gene. Experiments performed with free-living bacteria indicated that trc genes were organized in at least four transcription units and that the substrate trigonelline was a specific inducer for three of them. Noninducing trigonelline-related compounds such as betaines appeared to antagonize the inducing effect of trigonelline. None of the general or symbiotic regulatory genes ntrA, dctB/D, or nodD seemed to be involved in trigonelline catabolism. trc fusions exhibiting a low basal and a high induced [beta]-galactosidase activity when present on pSym were used to monitor trc gene expression in alfalfa tissue under symbiotic conditions. Results showed that trc genes are induced during all the symbiotic steps, i.e., in the rhizosphere, infection threads, and bacteroids of alfalfa, suggesting that trigonelline is a nutrient source throughout the Rhizobium-legume association.

Chromosomal DNA patterns and mitochondrial DNA polymorphism as tools for identification of enological strains of Saccharomyces cerevisiae

Abstract: Chromosomal DNA patterns using the transverse alternating field electrophoresis technique and mitochondrial DNA restriction profiles have been achieved for 22 enological strains of Saccharomyces cerevisiae. Both methods have evidenced a marked polymorphism of these strains. Twenty different karyotypes and 17 mitochondrial DNA banding patterns have been observed. Only three strains originating from the same vineyard could not be differentiated by either of the two methods. The polymorphism observed at the chromosomal and mitochondrial levels makes the techniques investigated powerful tools for identification and control of industrial strains.

Genetic transformation using Agrobacterium rhizogenes.

Abstract: Agrobacterium rhizogenes transfers genes encoding phenotypic alterations that serve as morphological markers for the presence of foreign DNA. These alterations facilitate root culture and thus studies of roots and their interactions with their biological and physical environments. They also provide insights into how plants develop.

Evidence for a new major gene influencing meat quality in pigs.

Abstract: The present investigation primarily deals with the inheritance of a pigmeat quality trait, the Napole technological yield (RTN), a measure of cooked weight to fresh weight. This trait as well as lean percentage at 100 kg liveweight and fattening length from 20 to 100 kg liveweight were recorded on 3459 offspring from 67 sires and 433 dams, and 3052 offspring from 64 sires and 405 dams in Penshire (P66) and Pen Ar Lan (P77) composite lines respectively. The hypothesis of a major 2-allele locus contributing to RTN was tested by use of a segregation analysis method. Highly significant likelihood ratios (mixed vs. polygenic transmission models) lead us to conclude that a major gene RN- exerting an unfavourable effect on RTN is segregating in both lines. Maximum likelihood estimates of the parameters under the hypothesis of mixed (monogenic + polygenic) inheritance show that the difference between the means of the 2 homozygotes amounts to about 3 phenotypic standard deviations of the trait, whereas the complete dominance of RN- cannot be rejected. The frequency of RN- is about 0.6 in both lines. These results are discussed in connection with the previously reported 'Hampshire effect' on pigmeat quality, as the Hampshire breed is a common component of the foundation stock of the 2 composite lines under study.

Adaptation of the Photosynthetic Apparatus in Maize Leaves as a Result of Nitrogen Limitation : Relationships between Electron Transport and Carbon Assimilation

Abstract: In maize (Zea mays L., cv Contessa), nitrogen (NO3−) limitation resulted in a reduction in shoot growth and photosynthetic capacity and in an increase in the leaf zeaxanthin contents. Nitrogen deficiency had only a small effect on the quantum yield of CO2 assimilation but a large effect on the light-saturated rate of photosynthesis. Linear relationships persisted between the quantum yield of CO2 assimilation and that of photosystem II photochemistry in all circumstances. At high irradiances, large differences in photochemical quenching and nonphotochemical quenching of Chl a fluorescence as well as the ratio of variable to maximal fluorescence (Fv/Fm) were apparent between nitrogen-deficient plants and nitrogen-replete controls, whereas at low irradiances these parameters were comparable in all plants. Light intensity-dependent increases in nonphotochemical quenching were greatest in nitrogen-deficient plants as were the decreases in Fv/Fm ratio. In nitrogen-deficient plants, photochemical quenching decreased with increasing irradiance but remained higher than in controls at high irradiances. Thermal dissipative processes were enhanced as a result of nitrogen deficiency (nonphotochemical quenching was elevated and Fv/Fm was lowered) allowing PSII to remain relatively oxidised even when carbon metabolism was limited via nitrogen limitation.

The genetics of transient populations: Research at the metapopulation level

Abstract: The metapopulation concept allows us to generate new models, in which each single local population is in disequilibrium (from both demographic and genetic points of view) but the whole is stable. We review recent empirical and theoretical results showing the relevance of the metapopulation level, in particular for understanding the evolution of those traits that do not experience the same selective forces during the different demographic stages of each local population.