C. Pavan

Nitrogen-fixing chemo-organotrophic bacteria isolated from cyanobacteria-deprived lichens and their ability to solubilize phosphate and to release amino acids and phytohormones.

Aims:  Cyanobacteria‐deprived lichens of the species Canoparmelia caroliniana, Canoparmelia crozalsiana, Canoparmelia texana, Parmotrema sancti‐angeli and Parmotrema tinctorum were screened for the presence of chemo‐organotrophic nitrogen‐fixing bacteria.

Nuclear Polyhedrosis Virus: A Possible Example of De Novo Intranuclear Membrane Morphogenesis

Membranes are intimately involved in the life-cycle of nuclear polyhedrosis viruses (NPV), and the related (Bellett, 1969) granulosis viruses (GV). Generally, two different types of membrane are seen, which we categorize as envelopes and ‘transport’ membranes. The former represent those membranes which closely surround mature, occluded, nucleocapsids and which are also involved in the initial membrane fusion event thought necessary for virus uptake by midgut epithelial cells (Harrap, 1970; Summers, 1971; Kawanishi et al. 1972). The acquisition of envelopes is also a necessary requisite for occlusion (Summers & Arnott, 1969), a process that usually occurs only in tissues other than the gut. ‘Transport’ membranes, on the other hand, are involved in the movement of non-occluded nucleocapsids from the site of primary (gut) infection to other tissues, such as fat body, in which the progeny of a second round of virus replication become occluded; unlike envelopes, these membranes are often vesicular in profile (Harrap, 1970; Summers, 1971).

Molecular characterization of nitrogen-fixing bacteria isolated from brazilian agricultural plants at São Paulo state

Fourteen strains of nitrogen-fixing bacteria were isolated from different agricultural plant species, including cassava, maize and sugarcane, using nitrogen-deprived selective isolation conditions. Ability to fix nitrogen was verified by the acetylene reduction assay. All potentially nitrogen-fixing strains tested showed positive hybridization signals with a nifH probe derived from Azospirillum brasilense. The strains were characterized by RAPD, ARDRA and 16S rDNA sequence analysis. RAPD analyses revealed 8 unique genotypes, the remaining 6 strains clustered into 3 RAPD groups, suggesting a clonal origin. ARDRA and 16S rDNA sequence analyses allowed the assignment of 13 strains to known groups of nitrogen-fixing bacteria, including organisms from the genera Azospirillum, Herbaspirillum, Pseudomonas and Enterobacteriaceae. Two strains were classified as Stenotrophomonas ssp. Molecular identification results from 16S rDNA analyses were also corroborated by morphological and biochemical data.

Virus-Chromosome Relationships In Cells Of Rhynchosciara (Diptera, Sciaridae)

SUMMARYSeveral infections of Rhynchosciara angelae by Rhynchosciara polyhedrosis virus (RPV) were studied. The virus multiplies within the nuclei of the cells of the intestinal caeca and the mid-intestine. The viruses cause the formation of unicellular tumors with greatly enlarged polytene chromosomes which may have constrictions at specific points. The nucleoplasm of the nuclei with enlarged chromosomes may be Feulgen-positive or -negative. Autoradiographic studies of nuclei of larvae injected with H3-thymidine indicate that the multiplication of the virus may be connected with the host chromosomal material. Four different constrictions may be induced by the virus in one of the enlarged chromosomes (A). These constrictions are located in the neighborhood of four thick bands, two of which are typically heterochromatic and the other two which, although not having the « vacuolized » aspect of heterochromatin, sometimes may ectopically pair with heterochromatic regions of the chromosomes. Several different s...

On lethals and their suppressors in experimental populations of Drosophila Willistoni

Abstract Naturally occurring and radiation-induced lethals were studied in experimental popu populations maintained in population cages. The populations were started with four lethals, two wild and two induced, each of them having frequency of 0.25. The lethals still had frequencies from 0.03 to 0.18 when the populations were 348 days old. The analysis of the lethals showed that all of them were able to survive in homozygous condition. The survival of the flies homozygous for the lethals was due to the presence of recessive suppressors. The proportion of the lethals accompanied by theirs own suppressors was measured in a sample taken when the populations were 866 days old and varied from 0 to 58.3%. The implications of the presence of suppressors regarding the behaviour of lethals in populations are analysed and discussed.

Studies on Cytology and Differentiation in Sciaridae. I. Chromosome Changes Induced by a Gregarine in Trichosia Sp. (Diptera, Sciaridae)

SUMMARYThis paper reports chromosomal changes induced by a gregarine in the parasitized caeca cells of Trichosia sp. The chromosomes of the host cells grow to abnormal sizes and present constrictions and breaks. The polytene chromosomes dissociate producing polyploid nuclei. There are also differential effects on the autosomes and X-chromosome. The system host cell- gregarine here reported is very favorable for studies on the regulation of chromosome metabolism as well as for the understanding of chromosomal effects of pathological agents.

Theodosius Dobzhansky and the development of Genetics in Brazil

Theodosius Dobzhansky was a great traveler and, during his adult life, he developed this tendency thoroughly. Greater even than his roving was his obsession to convey his ideas and theories to young and old people, not only to his North-American colleagues and students, but also to many other people in different parts of the world, wherever he could go. A great part, if not all, of his trips inside and outside the USA were connected with his research, with teaching or with helping people to organize their laboratories or research projects.

Studies on Cytology and Differentiation in Sciaridae IV. Nuclear and Cytoplasmatic Differentiation in Salivary Glands of Bradysia Elegans (Diptera, Sciaridae)

SUMMARYThe salivary glands of Bradysia elegans have five sharply differentiated regions, the cells of which have different cytoplasmic secretions. There is a concomitant differentiation of the nuclei and cytoplasms. The chromosomes do not have puffs during the larval period when the secretions are being produced, stored and eliminated. Large DNA and RNA puffs develop at the end of the larval period and during the prepupal stage. The absence of puffs in metabolically active cells and their late appearance are discussed. One of the regions has nuclei with largely unpaired homologous chromosomes, while the pairing is normal in all the other regions. This non-pairing of homologous segments of chromosomes in the cells of this particular regions is probably due to physiological causes rather than to genetic differences of the homologous chromosomes.