Recherches Cytochimiques sur la Microsporidie Nosema bomycis au cours de son Développement chez le Ver à Soie (Bombyx mori)*

RESUME. La Microsporidie Nosema bombycis, Protozoaire parasite agent de la pébrine du ver à soie, a étéétudiée cytochimiquement à la fois en microscopie photonique et électronique. Les examens ont porté sur la détection et la localisation des acides nucléiques (ADN et ARN), des polysaccharides, de la phosphatase acide, au cours des différents stades du développement dans les cellules de I'hôte (du schizonte à la spore). Les principaux résultats concernent les observations relatives aux polysaccharides et à la phosphatase qui ne sont détectés qu'au stade de la spore et ne sont pas observés au stade du schizonte. Les polysaccharides sont présents au niveau du sac polaire, du filament polaire et sur la membrane cytoplasmique; la phosphatase acide est localisée au niveau du sac polaire, du filament polaire et dans la vacuole postérieure. SYNOPSIS. Nosema bombycis, agent of pebrine disease of silkworm, was studied cytochemically, using both light and electron microscopy. Presence of nucleic acids (DNA and RNA), polysaccharides, and acid phosphatases was demonstrated and localization of these substances was determined in various stages of the parasite (from the schizont to the spore). DNA and RNA were detected in all these stages. Polysaccharides and acid phosphatase were found in the spore but not in the schizogonic stages. Polysaccharides were detected in the polar cap, the polar filament, and the limiting membrane of the cytoplasm of the spore. Acid phosphatase was found in the polar cap, the polar filament, and the posterior vacuole.     

Development of Stem Nodules in a Tropical Forage Legume, Aeschynomene afraspera

Rhizobial infection occurred on the stem of Aeschynomene afrasperaat the site of emergence of adventitious root primordia. Rhizobiainvaded cortical cells at the base of the root primordium. Thefirst infected cell enlarged and collapsed after rhizobia hadmultiplied in large numbers. At this time, a meristematic zonewas initiated some distance beneath the first infected cell.Rhizobial penetration into the deeper cortex was by progressivecollapse of infected cells towards the meristematic zone; rhizobiaentering the cortical cells by invagination of the host cellwall. At the entry point, rhizobia were embedded in digitatecell wall material. These infection structures were restricted,always originating from the cell wall of an adjacent infectedcell. Soon after infection, the cell collapsed progressivelyforming infection strand-like structures which developed upto the meristematic zone. When infection had reached the meristematiczone, invaded host cells ceased to collapse but divided repeatedlyto form the nodule. Key words: Aeschynomene afraspera, stem nodulation     

NERVOUS CONTROL OF OVULATION AND EJACULATION IN HELIX ASPERSA

The ovotestis duct transports male and female gametes from theovotestis, through the seminal vesicle, and into the fertilizationpouch-spermathecal complex. All these structures are innervatedby small branches of the intestinal nerve. Electrical stimulationof the nerve increased the rate at which gametes were transportedin the duct and caused autosperm to flow into the fertilizationpouch-spermathecal complex. These events were accompanied bystimulation-induced peristaltic contractions along the ductand activation of the cilia lining the interior of the duct.Acetylcholine and serotonin were identified as excitatory transmittersin this system, while FMRFamide was identified as a muscle relaxant.The nervous control of ejaculation may contribute to optimizingthe size of the ejaculate in a context of sperm competition,while the involvement of the nervous system in ovulation maystem from a requirement for sensory integration that is peculiarto the Stylommatophora. (Received 16 December 2004; accepted 31 March 2005)     

Influence de quelques acides aminés libres de l'ovule sur la croissance et le développement cellulaire in vitro du tube pollinique chez Juniperus communis (Cupressaceae)

Influence of some free amino acids of the ovule on growth and cellular development of the pollen tube of Juniperus communis L. in vitro. The extraction and analysis of free amino acids show that a partial complementary relationship exists between the amino acids of the pollen and those of the ovule of Juniperus communis. The main free amino acids of the pollen are threonine, proline, arginine and γ-aminobutyric acid; those of the ovule are threonine, serine, alanine, citrulline and glycine. The addition of the main amino acids of the ovule in the pollen culture media increased the growth and the cell development of pollen tubes cultured in vitro. This indicates the nature of the correlations which exist between the male and female gametophyte of Juniperus communis.     

A 10‐year decrease in plant species richness on a neotropical inselberg: detrimental effects of global warming?

The census of vascular plants across a 10-year interval (1995–2005) at the fringe of a neotropical rainforest (Nouragues inselberg, French Guiana, South America) revealed that species richness decreased, both at quadrat scale (2 m²) and at the scale of the inselberg (three transects, embracing the whole variation in community composition). Juvenile stages of all tree and shrub species were most severely affected, without any discrimination between life and growth forms, fruit and dispersion types, or seed sizes. Species turnover in time resulted in a net loss of biodiversity, which was inversely related to species occurrence. The most probable cause of the observed species disappearance is global warming, which severely affected northern South America during the last 50 years (+2 °C), with a concomitant increase in the occurrence of aridity.     

Influence des racines sur le développement végétatif ou floral des bourgeons cotylédonaires chez le Scrofularia arguta: role possible des cytokinines

Influence of roots on the vegetative or floral development of cotyledonary buds of Scrofularia arguta Sol.: A possible cytokinin role. This study shows that the presence of “nonabsorbing roots” insures a vegetative development of cotyledonary buds cultured in vitro whereas buds growing without roots produce flowers early. In the same way, roots suppress floral expression of axillary meristems of the same cotyledonary buds and induce these buds to vegetative functioning. Various trophic modifications in the culture medium are ineffective on non-rooted buds as also are gibberellin As and adenine. On the contrary, several cytokinins (kinetin, benzyladenine and zeatin) exert the same influence as roots. These results suggest that roots regulate meristematic functioning through cytokinins.     

Proteolytic activity in the ectoperitrophic fluid of blood-fed Culex nigripalpus

In blood-fed Culex nigripalpus Theobald, proteolytic activity appeared in the ectoperitrophic fluid after 3 h, but only after 6 h in a homogenate of the blood-filled midgut. The activity continued to be higher in ectoperitrophic fluid than in whole gut homogenate until about 40 h after the meal, when most of the intact clot had disappeared. Apparently, undigested blood inhibits proteolytic activity. The blood clot lacked activity and the inhibitor could not be removed by washing. The results are compatible with a hypothesis that the peritrophic membrane separates the digestion from the ingestion compartment.     

Development and plasticity of endangered shrub Lindera melissifolia (Lauraceae) seedlings under contrasting light regimes

Lindera melissifolia (Walt.) Blume seedlings were raised in a growth chamber to determine the effects of light availability on shoot growth pattern, and basic leaf and stem growth. Lindera melissifolia seedlings exhibited a sympodial shoot growth pattern for 3 months following emergence from the soil medium, but this pattern was characterized by a reduction in leaf blade area approximately 30 days after emergence, followed by increases in leaf blade area. Seedlings receiving low light were 76% taller than seedlings receiving high light. Seedlings receiving low light also had larger leaf blade dimensions, blade area, seedling leaf area, and greater mass. Seedlings raised in high light had a greater proportional distribution of biomass in the roots, suggesting possible water stress from greater vapor pressure deficits. Furthermore, these seedlings displayed sharp angles of blade inclination and blade folding – acclimation that reduces exposure to light and subsequent higher leaf temperatures in open environments. These differences in morphological response to light resulted in high phenotypic variability in L. melissifolia seedlings. Lindera melissifolia seedling development showed a brief period of phenotypic plasticity, followed by ontogenetic plasticity. The short period of phenotypic plasticity may, however, have profound ecological implications for the conservation and recovery of this federally endangered shrub. Further experimentation should take into account the development of ontogenetic standards for comparisons of plant traits in addition to temporal standards.