Serotyping of Toxoplasma gondii: striking homogeneous pattern between symptomatic and asymptomatic infections within Europe and South America

Field isolates of Toxoplasma gondii in Europe and North America have been grouped into three clonal lineages that display different virulence in mice. Whether the genetic structure of the parasite is related to clinical expression in humans has not yet been demonstrated. We developed an enzyme-linked immunosorbent assay which uses lineage-specific, polymorphic polypeptides derived from the dense granule antigens, GRA5 and GRA6. Our goal was to compare serotypical patterns observed in asymptomatic versus symptomatic (ocular disease and severe infection in human immunodeficiency virus (HIV)-positive patients) infections among patients from Europe and South America. Independent of the clinical presentation of the disease, serotypes differed according to geographical origin, with a homogeneous distribution of serotype II in Europe and of serotypes I and III in South America. We conclude that GRA5-GRA6 serotyping is an interesting tool to study serotype prevalence in populations but it is not an accurate marker of pathogenicity of Toxoplasma infection in humans.     

The integrative element pSAM2 from Streptomyces: kinetics and mode of conjugal transfer

pSAM2 is an 11 kb integrative element from Streptomyces ambofaciens that is capable of conjugal transfer. A system based on differential DNA modification by SalI methyltransferase was used to localize pSAM2 in the donor or recipient strain, and thus to determine the various steps associated with transfer. Initiation (i.e. excision and replication of pSAM2 in the donor) occurs a few hours after mating with a recipient strain. pSAM2 replicates in the recipient strain, spreads within the mycelium and then integrates into the chromosome. Transfer generally involves single-stranded DNA. In Streptomyces, only a few genes, such as traSA for pSAM2, are required for conjugal transfer. Using the differential sensitivity to the SalI restriction-modification system of transfers involving single- and double-stranded DNA, we found that pSAM2 was probably transferred to the recipient as double-stranded DNA. This provides the first experimental evidence for the transfer of double-stranded DNA during bacterial conjugation. Thus, TraSA, involved in pSAM2 transfer, and SpoIIIE, which is involved in chromosome partitioning in Bacillus subtilis, display similarities in both sequence and function: both seem to transport double-stranded DNA actively, either from donor to recipient or from mother cell to prespore.     

Analysis of energetic amino acid metabolism in Acyrthosiphon pisum: A multidimensional approach to amino acid metabolism in aphids

Aphids are highly specialized insects that feed on the phloem-sap of plants, the amino acid composition of which is very unbalanced. Amino acid metabolism is thus crucial in aphids, and we describe a novel investigation method based on the use of ¹⁴C-labeled amino acids added in an artificial diet. A metabolism cage for aphids was constructed, allowing for the collection and analysis of the radioactivity incorporated into the aphid body, expired as CO₂, and rejected in the honeydew and exuviae. This method was applied to the study of the metabolism of eight energetic amino acids (aspartate, glutamate, glutamine, glycine, serine, alanine, proline, and threonine) in the pea aphid, Acyrthosiphon pisum. All these amino acids except threonine were subject to substantial catabolism as measured by high ¹⁴CO₂ production. The highest turnover was displayed by aspartate, with 60% of its carbons expired as CO₂. For the first time in an aphid, we directly demonstrated the synthesis of three essential amino acids (threonine, isoleucine, and lysine) from carbons of common amino acids. The synthesis of these three compounds was only observed from amino acids that were previously converted into glutamate. This conversion was important for aspartate, and lower for alanine and proline. To explain the quantitative results of interconversion between amino acids, we propose a compartmentation model with the intervention of bacterial endosymbiotes for the synthesis of essential amino acids and with glutamate as the only amino acid supplied by the insect to the symbiotes. Moreover, proline exhibited partial conversion into arginine, and it is suggested that proline is probably indirectly involved in excretory nitrogen metabolism. © 1995 Wiley-Liss, Inc.     

Stimulation of root and somatic embryo production in Euonymus europaeus L. by an inhibitor of polyamine biosynthesis

In vitro formation of roots and somatic embryos is obtained from cotyledon explants of a Spindle tree (Euonymus europaeus L.) cultured on two different media: a medium inducing callus formation and the production of roots, and a medium inducing callus formation, root and somatic embryo production. We studied the effects of α-difluoromethylornithine (DFMO), a specific, irreversible inhibitor of ornithine decarboxylase (ODC) on root and somatic embryo production, growth and titers of putrescine in Euonymus explants and explant-derived calli. Early changes in putrescine levels were detected in both cultures before the visible emergence of roots or somatic embryos. DFMO rapidly inhibited putrescine accumulation and growth in non-embryogenic calli and highly stimulated rooting activity. DFMO partially inhibited putrescine accumulation in embryogenic calli. This inhibition had no effects on callus growth but significantly reduced the time of emergence of roots and highly stimulated somatic embryo production. The relationship among putrescine, putrescine metabolism, growth, root and somatic embryo formation is discussed.     

Transglutaminase-like activity in Chrysanthemum leaf explants cultivated in vitro in relation to cell growth and hormone treatment

In Chrysanthemum leaf explants cultivated in vitro the capacity to covalently link polyamines to protein substances exists. This plant enzyme activity shows some similarities with mammalian transglutaminases. In foliar explants cultured on a medium promoting bud or root formation increasing levels of transglutaminase-like activity occurred during the first days of culture when cell multiplication was rapid then the levels declined as the rate of cell division decreased and differentiation occurred. Undifferentiated callus exhibited low transglutaminase-like activity. Transglutaminase-like activity also increased in rapidly proliferating and growing organs (roots and buds initiated from the foliar explants) and decreased during maturity. The relationship among transglutaminases-like activity, cell division, bud and root formation is discussed.     

Effects of soil resistance to root penetration on leaf expansion in wheat (Triticum aestivum L.): composition, number and size of epidermal cells in mature blades

Wheat seedlings {Triticum aestivum L.) were grown on soils withcontrasted resistances to root penetration (measured as penetrometerresistance, R_s. High R_s reduced the rates of leaf appearanceand expansion. Although the duration of expansion was increased,mature leaves were smaller. Underlying changes in leaf anatomywere investigated on cleared mature leaves, focusing on theepidermes. Three leaves were analysed: leaves 1 and 3 whichstarted their development in the embryo, and leaf 5 which wasinitiated on the seedling, after imposition of contrasted soilconditions. In all leaves, high R_s, caused a reduction in maturecell sizes, lengths and widths, and a shift in the relativeproportions of functionally different cell types, with a decreasein the relative proportions of stomata and associated cell types(interstomatal and sister cells) and an increase in the proportionsof unspecialized elongated epidermal cells and of trichomes.In leaves 3 and 5 the number of cellular files across the bladewas also reduced, while in leaf 1 it was similar at the twoR_s. These differences between leaves are attributed to differencesin their developmental stage when root stress was first perceived.Remarkably, R_s had no effect (leaf 1) or relatively small effects(leaves 3 and 5) on the total number of cells per file, suggestingthat this parameter is either largely insensitive to variationin root environment, or is programmed at the outset before stresswas perceived at the apex. Key words: Wheat, anatomy, mature epidermis, root impedance     

The role of apical development around the time of leaf initiation in determining leaf width at maturity in wheat seedlings (Triticum aestivum L.) with impeded roots

High soil resistance to root penetration (measured as penetrometerresistance, R_s slows down leaf growth and reduces mature leafsize in wheat seedlings {Triticum aestivum L.). Underlying changesin the kinetics of cell partitioning and expansion and in thesize and organization of mature cells were reported in companionpapers (Beemster and Masle, 1996; Beemster et al., 1996). Inthe present study, the relationships between apex growth, primordiuminitiation and expansion were analysed for plants grown at contrastingR_s, focusing on a leaf whose whole development proceeded afterthe onset of root impedance (leaf 5). High R_s reduced the rates of apex and leaf development, butdid not appear to have immediate effects on the pattern of developmentof the newly initiated phytomers. During an initial short period,the rate of development of a leaf primordium and associatednode were related to plastochronic age, according to similarrelationships (slopes) at the two R_s. Effects on developmentalpatterns were first detected on phytomer radial expansion duringplastochron 2. The ontogenetic pattern of leaf elongation wasaffected later, during the next few plastochrons preceding leafemergence (‘post-primordial stage’). It is concludedthat a reduction in the number of formative divisions and inthe number of proliferative cells along the intercalary mer-istemreported earlier (Beemster and Masle, 1996; Beemster et al.,1996) is not related to the size of the apical dome at leafinitiation nor to the size and number of meristematic cellsinitially recruited to the leaf primordium, which were all unaffectedby R_s. Rather they are generated at the primordial and post-primordialstages. Key words: Wheat, apex development, leaf primodium development, mature leaf width, root impedance