Fine structure,mechanism of heart function and haemodynamics in the prosobranch gastropod molluscLittorina littorea (L.)

Summary The heart, main blood vessels, and associated structures ofLittorina littorea were examined by scanning and transmission electron microscopy. The auricle is subdivided into two compartments, one receiving blood from the gill and opening to the nephridial gland vein, the other connecting with the latter anteriorly and the ventricle posteriorly.Video recordings were made of the beating heart in vivo and revealed that the auricle expelled blood not only to the ventricle, but also the nephridial gland vein at systole and provided further evidence of tidal flow of blood in the vein. There is clear indication that the constant volume mechanism of auricular re-filling is not strictly true inLittorina.Blood pressure in the heart and major vessels was measured using a servo-nulling micropressure system. The rate of formation of urine (derived by filtration of blood through the auricular wall) was measured using [⁵¹Cr] EDTA as a blood marker.Basal blood pressure was slightly above ambient (0.7 cm H₂O). Peak systolic pressure in the ventricle (3.8 cm H₂O) was synchronised with a subambient trough in pericardial pressure (–1.0 cm H₂O); these pressure pulses were out of phase with that of the auricle (2.3 cm H₂O) at systole. The observations are consistent in broad terms with a constant volume mechanism, but this does not take into account urine formation or filling of the nephridial gland vein.A filtration pressure of 1.5 cm H₂O has been demonstrated across the auricular wall throughout the cardiac cycle. Colloidal back pressure appears to be negligible. The mean rate of urine formation is 0.26 l g^–1 min^–1.     

Host Status of Five Weed Species and Their Effects on Pratylenchus zeae Infestation of Maize

The host suitability of five of the most common weed species occurring in maize (Zea mays L.) fields in South Africa to Pratylenchus zeae was tested. Based on the number of nematodes per root unit, mealie crotalaria (Crotalaria sphaerocarpa) was a good host; goose grass (Eleusine indica), common pigweed (Amaranthus hybridus), and thorn apple (Datura stramonium) were moderate hosts; and khaki weed (Tagetes minuta) was a poor host. Only the root residues of khaki weed suppressed the P. zeae infestation of subsequently grown maize. When goose grass, khaki weed, and mealie crotalaria were grown in association with maize in soil infested with P. zeae, goose grass and khaki weed severely suppressed maize root development; this resulted in a low number of nematodes per maize root system and a high number of nematodes per maize root unit. Mealie crotalaria did not restrict maize root growth and did not affect nematode densities per maize root system or maize root unit. Special attention should be given to the control of mealie crotalaria, which is a good host for P. zeae, and goose grass, which, in addition to its ability to compete with maize, is also a suitable host for P. zeae.     

Missense mutation in the lacI gene of Escherichia coli. Inferences on the structure of the repressor protein

The lac repressor has been studied extensively but a precise three-dimensional structure remains unknown. Studies using mutational data can complement other information and provide insight into protein structure. We have been using the lacI gene-repressor protein system to study the mutational specificity of spontaneous and induced mutation. The sequencing of over 6000 lacI- mutations has revealed 193 missense mutations generating 189 amino acid replacements at 102 different sites within the lac repressor. Replacement sites are not distributed evenly throughout the protein, but are clustered in defined regions. Almost 40% of all sites and over one-half of all substitutions found occur within the amino-terminal 59 amino acid residues, which constitute the DNA-binding domain. The core domain (residues 60 to 360) is less sensitive to amino acid replacement. Here, substitution is found in regions involved in subunit aggregation and at sites surrounding residues that are implicated in sugar-binding. The distribution and nature of missense mutational sites directs attention to particular amino acid residues and residue stretches.     

Effects on growth and sporulation of inactivation of a Bacillus subtilis gene (ctc) transcribed in vitro by minor vegetative cell RNA polymerases (E-sigma 37, E-sigma 32)

Summary The E-³⁷ gene ctc was inactivated by a site-specific insertion into the Bacillus subtilis chromosome. The resulting mutation inhibited sporulation by 95% at elevated temperatures (48° C). If the ctc ^- mutation is placed in a strain that carries a mutation in the closely linked but distinct spoVC gene, ctc now affects both growth and sporulation at elevated temperatures. Growth of the ctc ^- spoVC285 strain was transiently inhibited when exponentially growing cultures were shifted from 37° C to 48° C. A similar, but less pronounced growth lag, was also seen in a B. subtilis strain carrying only the spoVC-285 mutation. This finding suggests that both the ctc and spoVC products function in vegetatively growing B. subtilis.     

Multiple variants in subtelomeric regions of normal karyotypes

We describe a human genomic cosmid clone, 56.1.1, that contains subtelomeric sequences present on multiple human chromosomes. In particular, using fluorescence in situ hybridization, we have identified 16 sites of hybridization on 12 chromosomes. In a sample of 8 unrelated individuals, 10 of these sites showed interindividual variation. Co-hybridization with other polymorphic probes allowed us to demonstrate cytologically heterozygosity at three sites in six individuals. The chromosomal distribution of hybridization sites in a family strongly suggests that these variants are inherited in a Mendelian fashion. These data show that subtelomeric repeats are a rich source of genetic variability. Possible mechanisms of generation of such variants are discussed.     

Surface heterogeneity of bovine sperm revealed by aqueous two-phase partition

Ejaculated, bovine sperm have been subjected to multiple partition in aqueous two-phase systems. This partition, carried out in a countercurrent fashion, reveals heterogeneity of the sperm population with respect to surface properties. The sperm, when partitioned in phase systems that detect non-change associated surface properties (change-insensitive) are largely distributed as two distinct populations. In charge-sensitive phase systems (which principally detect cell surface molecules carrying charge) the sperm do not show any obvious surface heterogeneity. Considerable heterogeneity is revealed in affinity-ligand phase systems containing palmitic acid coupled to one of the phase components-poly(ethylene glycol). There is a difference in surface heterogeneity between sperm which have been washed in buffer or left unwashed, direct from the ejaculate. This is indicative of weak adsorption of proteins to the sperm surface in seminal fluid. These results show that bovine ejaculated sperm is a heterogeneous cell population having unequal distributions of a number of different surface molecules.     

A survey of hospital toilet facilities.

OBJECTIVE--To assess the quality of toilet facilities available for disabled people in a large provincial teaching hospital. DESIGN--Survey of toilet facilities for patients on the wards and in the outpatient department. SETTING--Teaching hospital in Leeds. RESULTS--Although the quality of toilet facilities varied, none met the standards recommended by the British Standards Institution. The worst facilities were found on a ward accommodating elderly patients, where the toilets were unsuitable for use by disabled people and bedside commodes had to be used instead. CONCLUSION--Toilet provision within a major hospital failed to meet standards required for disabled people. Admission to hospital may therefore result in loss of independence and dignity. If hospitals are to be centres of excellence, greater consideration must be given to the requirements of disabled people in the design of new wards, and current inadequate facilities should be upgraded.