Geometric optics of trilobite eyes: a theoretical study of the shape of the aspherical interface in the cornea of schizochroal eyes of phacopid trilobites

A general method is given to determine theoretically the shape of the aspherical interface that eliminates spherical aberration in an optionally shaped thick lens. The theory is applied to trilobite eyes. On the basis of the geometric optical method presented, the refractive indices and focal length of the original corneal lenses of trilobites can be determined. The shape of the aspherical interface in the cornea of some phacopid trilobites with schizochroal eyes is investigated. The theoretical aspherical interfaces agree well with the real ones.     

Characteristics of NADPH-dependent thymidylate synthetase purified from Streptomyces aureofaciens.

NADPH-dependent thymidylate synthetase from Streptomyces aureofaciens has been purified to homogenity by a two-step chromatographic procedure including anion-exchange chromatography and affinity chromatography on methotrexate-Sepharose 4B. The enzyme was purified 1025-fold with a 34% yield. Basic characteristics of the enzyme were determined: molecular weight of the enzyme subunit (28,000), pH and temperature optimum, effect of cations, dependency on reducing agents, Km values for dUMP, mTHF, and NADPH (3.78, 21.1, and 38.9 microM, respectively), and inhibition effect of 5-FdUMP. Binding studies revealed the enzyme mechanism to be ordered sequential: dUMP bound before mTHF. S. aureofaciens thymidylate synthetase exhibits an absolute requirement for NADPH for the enzyme activity--a unique feature not displayed by any of the thymidylate synthetases isolated so far. NADPH is not consumed during enzyme reaction, indicating its regulatory role. The properties of S. aureofaciens thymidylate synthetase show that it is a monofunctional bacterial enzyme.     

Effect of cooling rate,cryoprotectant and holding time at different transfer temperatures on the survival of cryopreserved cell suspension culture (Puccinellia distans (L.) Parl.)

Reflexed saltmarsh-grass suspension cultures produced by seed callus were frozen to the liquid nitrogen temperature. Cooling rates, cryoprotectants and holding times were taken as a function of transfer temperatures. The highest survival of cells (45%) was found at a freezing rate of 1°C min^-1, without cryoprotectant treatments. The cryoprotectants (proline, dimethyl sulphoxide, glycerol), used at different concentrations and transfer temperatures, increased the survival rate. The maximum value was 78% at 12.5% (w/v) of proline with –30°C transfer temperature. Considerable improvement of viability (from 0% to 95%) among the 12.5 and 15.0% (v/v) dimethyl sulphoxide cryopreserved cells was achieved by holding them at – 20°C for 10–30 min before plunging into the liquid nitrogen. A 20 min holding time at 15.0% (v/v) glycerol level and – 30°C transfer temperature significantly enhanced the viability of the explants from 42% to 92%. Plants were successfully regenerated from cells cryopreserved with proline (w/v) and dimethyl sulfoxide (v/v) levels of 12.5 and 15.0%, respectively.     

Ryanodine receptor purified from crayfish skeletal muscle

The ryanodine receptor was isolated from the sarcoplasmic reticulum of crayfish skeletal muscle. Ryanodine binding to the native fraction was measured by Scatchard analysis and values of 60 nmol/l and 9 pmol/mg were obtained for KD and Bmax respectively. The identity of purified receptor was confirmed by electron microscopy, electrophoresis and incorporation into planar lipid bilayers. At least two conductance states (100 pS and 50 pS) were observed in 100 mmol/l NaCl both for native and purified receptor.     

Ultrastructural localization of silver-staining nuclear proteins at the onset of transcription in early bovine embryos.

Argyrophilic nuclear proteins, known to be functionally associated with ribosomal genes, were localized, in four-, eight-, and 16-cell bovine embryo blastomere nuclei using two different silver-staining procedures. Within the eight-cell cleavage stage by the process of embryonal nucleologenesis in the cow embryo the full-capacity ribosome-producing machinery is established. In the four-cell embryo, many patches and islands of argyrophilic (Ag+) material were detected in the nucleoplasm. The nucleolus-precursor bodies (NPBs), composed uniformly of a homogeneous compact mass, were completely devoid of any silver staining. On the other hand, clear-cut localization of argyrophilic proteins was detected during the eight-cell stage either inside the transforming NPBs or in the close vicinity, or in the already differentiated nucleolus. In compact, nonvacuolated NPB, an intensive Ag+ area was detected, in the form of a lenticle, at the periphery of the NPB. During and following vacuolation of the NPB, no Ag+ was detected inside these vacuoles. It was seen, however, in the dense fibrillar nucleolar component surrounding the smaller vacuoles formed at the time of the establishment of nucleolar structure. Ag+ areas were seen repeatedly in the vicinity of NPBs, probably a part of the nucleolus-associated chromatin or, alternatively, representing the extranucleolar bodies. In blastomere nuclei of 16-cell embryos, already possessing reticulated nucleoli known from intensively synthesizing somatic cells, the silver-staining pattern corresponded to the usual situation in differentiated cells: slight staining of fibrillar centers, heavy labelling in the dense fibrillar component, and absence of silver deposits in the granular component.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ecotoxicological contamination processes: Interaction with vegetation (a review)

Up-to-date crop production concentrates on the maximisation of plant matter production, both by optimum utilization of solar energy by plants and by the application of additional energy. Therefore a natural strategy is being developed aimed at combining the physiological functions of the assimilation organs with their external shaping and strengthening their variety in space and area. As demonstrated by many deposition studies, this effect is contradictory to the factors conditioning the low deposition capacity of plant covers. A high level of particle, gas and solution deposition increases the danger of food chain contamination and has a negative impact on plant production. Data concentrated on transport values of pollutants and their long-term dynamics in stands could be used for the selection of ideal crop types; therefore every effort should be directed towards selection and breeding.     

Molecular evidence of a lignin peroxidase H8 homologue inFusarium oxysporum

We describe an evidence for the existence of a ligninase isoenzyme H8 in the deuteromyceteFusarium oxysporum on the genomic as well as on the RNA level.     

Replication banding in the chromosomes of the European eel (Anguilla anguilla)

The chromosomes of the European eel Anguilla anguilla have been analyzed with a replication banding technique from lymphocyte cultures treated with 5-BrdU. This technique allows us to identify with high resolution the individual chromosome pairs and to differentiate classes of chromatin by the order of replication. The replication banding obtained on the chromosomes of European eel can be related with the structural bands described in this species.     

Establishment of transformed root cultures of Perezia cuernavacana producing the sesquiterpene quinone perezone

Summary The sesquiterpene quinone currently known as perezone is abundantly produced by the roots of Perezia cuernavacana. This compound is of biotechnological interest since it may be used as a pigment and has several pharmacological properties. In this work we demonstrate that perezone is also produced in transformed root cultures of P. cuernavacana. Hairy roots were induced by inoculation of internodal segments of sterile plants of P. cuernavacana with Agrobacterium rhizogenes AR12 strain. The axenic liquid MS medium cultures of the hairy roots isolated from the internodes showed active growth in the absence of growth regulators. The transformed nature of the tissue was confirmed by genomic integration (PCR and slot blot hybridization) and expression (enzyme activity) of the marker gus-gene. The production of perezone by a transformed root culture was evidenced by IR spectroscopy. Our results offer an alternative for enhanced production of perezone and represent an advantage over its extraction from natural plant populations which present problems in their agronomic culture.