Gamete formation reflects the sexual pheromone hierarchy ofDictyostelium giganteum

Summary Sexual development inDictyostelium giganteum begins with the appearance of small, amoeboid gametes that fuse to produce mainly binucleate cells which differentiate into zygote giant cells. The data presented here show that the number of gametes produced by each strain (WS589>WS606>WS607>WS588) is directly related to its position in this hierarchy.This work was supported by a grant (A6807) from the Natural Sciences and Engineering Research Council of Canada.     

The oak processionary caterpillar (Thaumetopoea processionea L.) an urticating caterpillar related to the pine processionary caterpillar (Thaumetopoea pityocampa Schiff.) (Lepidoptera,Thaumetopoeidae)

Summary The hairs ofThaumetopoea processionea caterpillars (Lepidoptera) provoke a cutaneous reaction in man and animals. The urticating apparatus, the urticating gland which produces hairs, and the urticating hairs, are similar to those of theT. pityocampa caterpillar. The irritant fraction extracted from hairs contains soluble proteins; one of these shows immunological identity with thaumetopoein, the urticating protein of theTh. pityocampa caterpillar. This thaumetopoein-like protein is currently undergoing isolation and will be subjected to dermatological tests.     

‘Waldsterben’, part IV (continuing series)

Summary Peroxidase and superoxide dismutase activities, and ascorbic acid content, were measured in both intercellular fluid and cell material of current and 1-year-old needles of Norway spruce saplings treated with ozone, ambient air and activated carbon-filtered air in outdoor fumigation chambers. Ethylene evolution was also compared. Plants from carbon-filtered air treatments had significantly lower enzyme activities and higher ascorbic acid content. These changes were more marked in intercellular fluid than in cell material. Significant changes were noted at ozone levels typical of ambient air quality in a typical urban area. These results suggest the need for simultaneous screening of several biochemical markers as a way of overcoming the lack of specificity of any single marker for the identification of a perturbation by a particular stress, such as ozone.Acknowledgments. This work was supported in part by Grant Number 4849-0.85 (NFP 14) from the Swiss National Fund of Scientific Research. We thank Dr. F. Cupelin and Dr. J. Cl. Landry from the Service d'Ecotoxicologie, Genève, who provided the facilities for the monitoring of ozone levels. We also thank A. Mesrobian, A. Rossier and D. Voluntaru for technical assistance. Du Pont de Nemours International is gratefully acknowledged for the gift of TEDLAR (polyvinyl fluoride film) to build up the fumigation chambers.     

Transformation: a tool for studying fungal pathogens of plants

Plant diseases caused by plant pathogenic fungi continuously threaten the sustainability of global crop production. An effective way to study the disease-causing mechanisms of these organisms is to disrupt their genes, in both a targeted and random manner, so as to isolate mutants exhibiting altered virulence. Although a number of techniques have been employed for such an analysis, those based on transformation are by far the most commonly used. In filamentous fungi, the introduction of DNA by transformation typically results in either the heterologous (illegitimate) integration or the homologous integration of the transforming DNA into the target genome. Homologous integration permits a targeted gene disruption by replacing the wild-type allele on the genome with a mutant allele on transforming DNA. This process has been widely used to determine the role of newly isolated fungal genes in pathogenicity. The heterologous integration of transforming DNA causes a random process of gene disruption (insertional mutagenesis) and has led to the isolation of many fungal mutants defective in pathogenicity. A big advantage of insertional mutagenesis over the more traditional chemical or radiation mutagenesis procedures is that the mutated gene is tagged by transforming DNA and can subsequently be cloned using the transforming DNA. The application of various transformation-based techniques for fungal gene manipulation and how they have increased our understanding and appreciation of some of the most serious plant pathogenic fungi are discussed. Received 9 May 2001; received after revision 2 July 2001; accepted 3 July 2001     

Amino-acid synthesis in carbonaceous meteorites by aqueous alteration of polycyclic aromatic hydrocarbons

It has been suggested that amino acids and other organic compounds found in carbonaceous meteorites formed by aqueous alteration in the meteorite parent bodies. Observations of carbonaceous material in interstellar grains and interplanetary dust particles indicate that condensed organic compounds may have been present in meteorite parent bodies at the time of aqueous alteration. One group of compounds thought to be representative of this carbonaceous material is the polycyclic aromatic hydrocarbons (PAHs). Recently it was proposed that PAHs condense on SiC grains in the molecular envelopes of carbon-rich red-giant stars, which would allow for their subsequent incorporation into meteorite parent bodies during accretion. This incorporation mechanism is supported by the identification of SiC grains in carbonaceous chondrites. The possibility therefore exists that PAHs, and/or other condensed organic compounds, represent the starting material for aqueous alteration which leads to the formation of amino acids and other water-soluble organic compounds. Here we present calculations of the distribution of aqueous organic compounds in metastable equilibrium with representative PAHs as functions of the fugacities of O2, CO2 and NH3. The results reported here for pyrene and fluoranthene, two PAHs with different structures but the same stoichiometry, differ greatly but indicate that the formation of amino and carboxylic acids is energetically favourable at probable parent-body alteration conditions. The actual reaction mechanisms involved could be revealed by consideration of isotope data for PAHs, amino acids, other organic compounds and carbonates in carbonaceous chondrites.     

Saccadic oscillations facilitate ocular perfusion from the avian pecten

THE evolution of the eye is constrained by two conflicting requirements--good vascular perfusion of the retina, and an optical path through the retina that is unobstructed by blood vessels. Birds are interesting in that they have higher metabolic rates and thicker retinas than mammals, but have no retinal blood vessels. Nutrients and oxygen must thus reach the neurons of the inner retina either from the choroid through 300 micron of metabolically very active retina, or from the pecten, a pleated vascular structure protruding from the head of the optic nerve into the vitreous chamber, and more than a centimetre away from some retinal neurons. Despite the diffusional distance involved, several lines of evidence indicate that the pecten is the primary source of nutrients for the inner retina: the presence of an oxygen gradient from pecten to retina, the large surface area produced by macroscopic folds and by microscopic infoldings of the luminal and external surfaces of the capillary endothelium, extrusion of circulating fluorescein, high content of carbonic anhydrase and alkaline phosphatase, and retinal impairments after pecten ablation. Another peculiarity of birds, their saccadic oscillations, occur with a large cyclotor-sional component during every saccadic eye movement. In different species, saccades, which occur at intervals of 0.5-40 s, have up to 13 oscillations with frequencies of 15-30 Hz and ampliá-tudes of about 10 degrees. Therefore, as much as 12% of some birds' total viewing time may be subject to the image instability caused by the oscillations. Using fluorescein angiography, we show here that during every saccade, the pecten acts as an agitator which propels perfusate towards the central retina much more effectively than is observed during intersaccadic intervals.     

In vivo alteration of telomere sequences and senescence caused by mutated Tetrahymena telomerase RNAs.

Mutating the CAACCCCAA sequence in the RNA component of telomerase causes the synthesis in vivo of new telomere sequences corresponding to the mutated RNA sequence, demonstrating that the telomerase contains the template for telomere synthesis. These mutations also lead to nuclear and cell division defects, and senescence, establishing an essential role for telomerase in vivo.     

Atomic structure of a fragment of human CD4 containing two immunoglobulin-like domains.

The structure of an N-terminal fragment of CD4 has been determined to 2.4 A resolution. It has two tightly abutting domains connected by a continuous beta strand. Both have the immunoglobulin fold, but domain 2 has a truncated beta barrel and a non-standard disulphide bond. The binding sites for monoclonal antibodies, class II major histocompatibility complex molecules, and human immunodeficiency virus gp120 can be mapped on the molecular surface.