Ultrastructural analysis of sperm flagella in two clitellates (Annelida), plasma membrane and periaxonemal area

The region between axonemes and plasma membrane in the sperm tails of the tubincid oligochaetes Tubifex tubifex and Monopylephorus limosus has been studied by means of thin sections of conventionally and tannic acid fixed material, and of freeze-fracture replicas. The main portion of the flagellum in both species showed prominent, regularly repeating bridges connecting doublets to plasma membrane. In correspondence to the doublets, characteristic double rows of intramembrane particles are present, with an arrangement reminiscent of the "zipper lines" described in other species. A well-developed cortical web with a honeycomb appearance underlies the plasma membrane. Glycogen granules are regularly arranged within the cells. An outstanding difference between the two species is to be found in the presence only in Monopylephorus of complex muff-like structures apparently formed by membrane particles and series of teeth embedded in the cortical web. Nothing similar has been found in Tubifex. This difference may be related to the fact that spermatozoa in Monopylephorus are not enclosed in spermatozeugmata as are those of Tubifex.     

The eggshell of the cherry fly Rhagoletis cerasi

One of the major pests in Greek cherry orchards is the cherry fly Rhagoletis cerasi (Diptera: Tephritidae). In order to complete our comparative work on the chorion assembly of other representatives of the fruit flies (e.g. Ceratitis capitata and Dacus oleae) we studied eggshell morphogenesis in the cherry fly. The oocyte is surrounded by several distinct layers which are produced during choriogenesis. The eggshell consists of the vitelline membrane, a fibrous layer of possible water-proofing function, an innermost chorionic layer, endochorionic and exochorionic layers. The endochorion shows a branched configuration with irregular cavities, and the exochorion consists of inner and outer layers for better embryo protection. At the anterior region of the follicle, the hexagonal borders of the follicle cells are created by endochorionic material, covered by both inner and outer exochorion. This area resembles the D. melanogaster chorionic appendages and therefore can serve for plastron respiration. The structural results support the phylogenetic relationships among the tephritids (Rhagoletis is closer to Ceratitis than Dacus). The presence of peroxidase in the endochorion, detected by diaminobenzidine, is consistent with the eggshell hardening at the end of choriogenesis, following the same pattern with the other fruit flies studied so far. Two major chorionic proteins are found both in R. cerasi and in C. capitata and therefore general conclusions can be drawn from this study, concerning the pattern of choriogenesis, which all dipteran insects follow, in order to create a resistant and functional eggshell, and the high conservation of the proteinaceous components of the chorion among species in the order.     

Real-time ultrasonic biparietal diameter measurement for the prediction of gestational age in llamas

Llama (Lama glama ) fetuses (n = 25) of known gestational age (Day 66 to Day 235) were examined transabdominally using real-time ultrasound with a 5 MHz linear-array scanhead. Maximum head width, or biparietal diameter (BPD), was measured in symmetrical images using electronic linear distance calipers. The fetus was easily located and the BPD measured as early as Day 66 of gestation. During the last trimester, measurement became increasingly difficult due to the posture of the fetus and the limited penetration of the 5 MHz frequency. The relationship between days of gestational age (GA) and mean BPD in millimeters is described by the equation: [GA = 18.8 + 3.79 BPD]. Assignment of gestational age allows estimation of parturition date in this frequently pasture-bred and newly polular domestic ruminant.     

Ultrasonic biparietal diameter of second trimester Pygmy goat fetuses

Four does pregnant with seven Pygmy goat fetuses were scanned transabdominally from Day 36 to Day 102 of gestation using a real-time ultrasound 5 MHz linear-array scanhead. Fetal biparietal diameter (BPD) was measured on symmetrical frozen images using internal electronic calipers. The relationship between gestational age (GA) in days and BPD in millimeters in Pygmy goat fetuses is expressed as: [GA = 23.2 + 2.08 BPD]. This equation can assign GA to Pygmy goat fetuses of unknown conception dates and allow confinement of does near kidding for induced or observed parturition. Mean kid birthweight was 2.0 + 0.45 kg SEM. These observations are consistent with relationships which have been determined for Toggenburg, Nubian and Angora goat fetuses.     

The use of the probit model to predict pregnancy status of buffalo based on physio-chemical properties of estrual mucus

Improper timing of artificial insemination with respect to ovulation is one of the major factors hampering the conception rate in buffalo. The present study was an attempt to relate physio-chemical changes in estrual mucus to subsequent pregnancy status in order to find their optimal values for determining the time for artificial insemination (AI). Serum estradiol, total protein and dry matter contents of estrual mucus were evaluated to predict the subsequent pregnancy in 36 buffalo during October 1988 to February 1989. Serum estradiol was determined by radioimmunoassay (RIA); spinnbarkeit, dry matter and total protein were determined by standard methods. Multivariate probit analyses were carried out to relate these variables to subsequent pregnancy status. Elasticity and protein concentration were significantly related to prediction probability of pregnancy status, and they predicted the pregnancy status 86% of the times correctly (P < 0.05). The probability of pregnant animals being correctly classified was 0.76, whereas the corresponding value for non-pregnant animals was 0.95. The present study demonstrated the possibility of using such a statistical model on mucus characteristics for determining proper AI time for better conception rates in Nili-Ravi water buffalo.     

NH(4)-Excreting Azospirillum brasilense Mutants Enhance the Nitrogen Supply of a Wheat Host

Spontaneous ethylenediamine-resistant mutants of Azospirillum brasilense were selected on the basis of their excretion of NH(4). Two mutants exhibited no repression of their nitrogenase enzyme systems in the presence of high (20 mM) concentrations of NH(4). The nitrogenase activities of these mutants on nitrogen-free minimal medium were two to three times higher than the nitrogenase activity of the wild type. The mutants excreted substantial amounts of ammonia when they were grown either under oxygen-limiting conditions (1 kPa of O(2)) or aerobically on nitrate or glutamate. The mutants grew well on glutamate as a sole nitrogen source but only poorly on NH(4)Cl. Both mutants failed to incorporate [C]methylamine. We demonstrated that nitrite ammonification occurs in the mutants. Wild-type A. brasilense, as well as the mutants, became established in the rhizospheres of axenically grown wheat plants at levels of > 10 cells per g of root. The rhizosphere acetylene reduction activity was highest in the preparations containing the mutants. When plants were grown on a nitrogen-free nutritional medium, both mutants were responsible for significant increases in root and shoot dry matter compared with wild-type-treated plants or with noninoculated controls. Total plant nitrogen accumulation increased as well. When they were exposed to a N(2)-enriched atmosphere, both A. brasilense mutants incorporated significantly higher amounts of N inside root and shoot material than the wild type did. The results of our nitrogen balance and N enrichment studies indicated that NH(4)-excreting A. brasilense strains potentially support the nitrogen supply of the host plants.     

Involvement of an Extracellular Glucan Sheath during Degradation of Populus Wood by Phanerochaete chrysosporium

Observations by transmission electron microscopy of wood samples of Populus tremula inoculated with the white rot fungus Phanerochaete chrysosporium showed that, at certain stages of their growth cycle, hyphae were encapsulated by a sheath which seems to play an active role in the wood cell wall degradation. Chemical and immunochemical techniques and C nuclear magnetic resonance spectroscopy were applied to demonstrate the beta-1,3-1,6-d-glucan nature of the sheath. Double-staining methods revealed the interaction between the extracellular peroxidases involved in lignin degradation and the glucan mucilage. The glucan was also shown to establish a material junction between the fungus and the wood cell wall. It was concluded that, by means of these interactions, the sheath provides a transient junction between the hyphae and the wood, thus establishing a point of attachment to the site of the degradation. The association of peroxidases to the glucan matrix is in favor of the role of the sheath as a supporting structure. Furthermore, that the sheath was hydrolyzed during the attack demonstrated its active role both in providing the H(2)O(2) necessary to the action of peroxidases and in providing a mode of transport of the fungal enzymes to their substrates at the surface of the wood cell wall.     

The evolution of developmental strategy in marine invertebrates

Developmental mode varies widely in most animal phyla. These differences in developmental strategy exert a profound influence on the ecology and evolution of closely related species. The mechanistic alterations in ontogeny that lead to switches in developmental mode are coming under increasing scrutiny. Echinoids are one of the best-understood groups in this regard. Parallel modifications in direct-developing echinoids point to some of the key changes in oogenesis and embryogenesis that produce switches in developmental mode.     

Cryptic dioecy in flowering plants

In some dioecious plant species, mates and/or females have large and presumably costly opposite-sex structures that are sterile. This is termed 'cryptic dioecy'. Several new cases of cryptic dioecy have recently been studied. They may give information about the minimal requirements for the evolution of separate sexes from hermaphroditism, because the most important differences contributing to the initial advantage of the breeding system have not been obscured by further developments. Reviewed in this light, cryptic dioecy can provide evidence on the role of reallocation of reproductive resources in the evolution of dioecy.