Resistance in tomato to the greenhouse whitefly: analysis of population dynamics

Life history parameters including longevity, developmental time, and reproduction were determined for whiteflies, Trialeurodes vaporariorum (Westwood), kept in clip-on cages on susceptible parent, Lycopersicon esculentum, resistant parent, L. hirsutum glabratum, and intermediate breeding lines of tomato. Using the Lewontin triangular reproductive function, the intrinsic rate of increase (r_m) was calculated for each genotype. This is an elegant tool for detecting resistance, as it incorporates all salient factors of life history. Comparing r_m to the other parameters measured, selection criteria were chosen. Developmental time is not a suitable selection criterion as it varies very little even between the most susceptible and the most resistant genotypes. Additionally, developmental time of T. vaporariorum offspring was found to be highly significantly correlated to parental age on all tomato genotypes except L. hirsutum glabratum. Total reproduction, truncated population counts, and longevity appear good criteria for selection. This test, focusing on antibiotic factors, shows large differences between the resistant and susceptible parent genotypes, but much smaller differences between the breeding lines and the susceptible parent. Earlier screenings relying on a variety of tests appear to have maintained antixenotic rather than antibiotic properties in the breeding lines.     

Chloroplast phosphoribulokinase associates with yeast phosphoriboisomerase in the presence of substrate

Pea chloroplastic phosphoribulokinase and yeast phosphoriboisomerase partition independently of one another in a two-phase polyethyleneglycol, dextran system, but apparent interaction is seen when ribose-5-phosphate is added to the two-phase system. It appears that the pea leaf of kinase recognizes yeast isomerase when it is carrying metabolite.     

Identification and population dynamics of bacteria in leaf spots of soybean

The qualitative and quantitative composition of bacterial flora occurring inside the leaf spots of field grown soybeans was studied during the growing seasons (June to October) of 1989 and 1990. As a rule these leaf spots (necrotic lesions with chlorotic haloes) were caused by Pseudomonas syringae pv. glycinea. This pathogenic bacterium was predominantly found during the whole season in the symptomatic leaf tissue. Other species, mainly Erwinia herbicola, were also found in the same habitat. The population sizes of P. s. pv. glycinea increased from the beginning of symptom occurrence until July, stabilized until September, and then decreased a little. In general, the size of saprophytic populations was orders of magnitude lower than that of the pathogenic populations. The number of different bacterial genera per sample increased up to four genera per leaf spot by the end of the season. No significant influence of the occurring saprophytes on the population dynamics of the pathogen in planta could be observed. Send offprint requests to: Dr. Beate Völksch, Friedrich Schiller University Jena, Biological Faculty, Institute of Microbiology, Pbilosophenweg 12, D/0-6900 Jena, Germany.     

Surface heterogeneity of rat sperm during maturation

Rat sperm isolated from the caput and caudal epididymis and the vas deferens were subjected to multiple partition in aqueous two-phase systems. The technique was used to reveal heterogeneity of a sperm population with respect to particular surface properties. Sperm from all three regions gave broad distributions indicative of heterogeneous cell populations. Greatest heterogeneity was observed for cauda sperm with caput and was sperm producing similar distributions.Following multiple partition sperm from different regions of the distribution profiles were immunostained with three antibodies known to recognise maturation antigens. The results show that some antigens are acquired during epididymal transit whilst others are present throughout.The partition (surface heterogeneity) seen cannot therefore be explained solely by the distribution of the antigens recognised by 2D6, 6B2 and 3D5.     

Ultrastructure of scales in a teleost (Carassius auratus L.) after use of rapid freeze-fixation and freeze-substitution

Summary New data on the ultrastructural features of the elasmoid scales ofCarassius auratus have been obtained by use of rapid freezing with subsequent freeze-substitution in anhydrous solvents. These are compared with the results obtained using conventional aqueous fixatives.The external layer of the scales is composed of randomly oriented collagen fibres. In the first stages of mineralization, mineral deposits are located in the interfibrillary substance where dense granules appear to be active sites of mineralization. Spheritic mineralization occurs in this layer.The fibrillary plate is composed of two kinds of collagen fibres. Most of them are organized in lamellae forming the plywood-like structure. They are thicker than the so-called TC fibres, which are oriented from the basal part towards the superficial layer. These TC fibres are involved in the first stages of mineral deposition in the fibrillary plate where inotropic mineralization occurs.The mineral phase is almost always located in the interfibrillary matrix in both layers of the elasmoid scale. In this respect, teleost scales differ from those described so far in other lower vertebrates.

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Resumé Des précisions concernant les aspects ultrastructuraux des dépôts minéraux dans les écailles deCarassius auratus ont été obtenues grâce à l'utilisation de la congélation ultra-rapide suivie d'une cryosubstitution en milieu anhydre. Ces données sont comparées à celles fournies par les méthodes usuelles utilisant des fixateurs aqueux.La couche externe des écailles comprend des fibres collagènes disposées sans ordre apparent. Les dépôts minéraux se produisent surtout dans la substance interfibrillaire où des granules denses semblent représenter des sites actifs au cours de la minéralisation apparentée au type sphéritique.La plaque basale comporte deux catégories de fibres collagènes. Les unes, les plus nombreuses, de plus fort diamètre, sont organisées en lamelles formant une structure en contre-plaqué; les autres appelées fibres TC, orientées de la base de l'écaille vers la zone superficielle, jouent un rôle important dans les premières phases de la minéralisation de type inotropique dans cette partie de l'écaille.Dans les deux couches de l'écaille, la phase minérale est surtout trouvée dans la substance interfibrillaire. De ce fait, les écailles élasmoides des Téleostéens peuvent être distinguées des autres écailles dermiques connues de Vertébrés inférieurs.

     

Dark modulation of NADP-dependent malate dehydrogenase and glucose-6-phosphate dehydrogenase in the chloroplast

The properties of the system which reverses light modulation of NADP-dependent malate dehydrogenase and glucose-6-phosphate dehydrogenase activity in pea chloroplasts were examined. A factor catalyzing dark modulation of these enzymes was found. This factor cochromatographed with thioredoxin in all systems used (Sephacryl S-200, Sephadex G-75, DEAE-cellulose). Inhibition of dithiothreitol-dependent modulation and of dark reversal by antibody against Escherichia coli thioredoxin further suggest that the dark factor is in fact thioredoxin. It appears that the reaction is the reverse of the previously described dithiothreitol-dependent thioredoxin-catalyzed modulation of enzymes. The limiting step in vitro seems to be the oxidation of thioredoxin during the dark period.     

Characterization of postreplication repair in Saccharomyces cerevisiae and effects of rad6, rad18, rev3 and rad52 mutations

Summary Postreplication repair of nuclear DNA was examined in an excision defective haploid strain of yeast lacking mitochondrial DNA (ral ⁰). The size of the DNA synthesized in cells exposed to various fluences of ultraviolet light (UV) corresponds approximately to the average interdimer distance in the parental DNA. Upon further incubation of cells following exposure to 2.5 J/m², the DNA increases in size; by 4 h, it corresponds to DNA from uniformly labeled cells. The alkaline sucrose sedimentation pattern of DNA pulse labeled at various times after UV irradiation, for up to 4 h, does not change substantially, indicating that dimers continue to block DNA replication. A significant amount of postreplication repair requires de novo protein synthesis, as determined by its inhibition by cycloheximide. The rad6 mutant does not carry out postreplication repair, the rad18 and rad52 mutants show great inhibition while the rev3 mutation does not affect postreplication repair. Both recombinational and nonrecombinational repair mechanisms may function in postreplication repair and most of postreplication repair is error free.