A light and electron microscopic study of stigmas inAneilema andCommelina species (Commelinaceae)

Summary The stigmas of species inAneilema andCommelina are trifid and comprise elongate papillae. Progressive degeneration of papular cells is observed in stigmas from open flowers and at anthesis papillae may be moribund and collapsed. Fluid emanating from the hollow style flows onto the surface through ruptures in the cuticle at the interpapillar junctions into the interstices at maturity. This secretion stains positively for protein. Stigmas are of the wet type.The cuticle overlying the papillar cells is ridged and at the final stages prior to flowering this cuticle becomes detached from the underlying cellulosic wall. The sub-cuticular space so formed is filled with secretion. InAneilema species detachment of cuticle is at the papillar tip and along the lateral walls. InCommelina species the anticlinal walls of adjacent papillae are strongly attached for much of their length and thus detachment of cuticle is restricted to the papillar tip. The cell wall at the tip in both genera may proliferate forming a rudimentary transfer-cell type wall. The secretion is considered to be produced by the papillar cells. It is PAS positive but fails to stain for protein and in both the light and electron microscopes appears heterogenous.Pollen attachment, hydration, germination and early tube growth are very rapid following self-pollination, the pollen tubes entering the neck of the style within ten minutes of attachment.A unique character combination involving pollen and stigmas in these genera indicates a monophyletic origin.     

Relation between diameter and flow in branches of the bronchial tree

Two methods are described for calculating the value of the exponentx in the equation flow =k×diameter ^x , as pertaining to a branch of the bronchial tree. In the lungs from three humans, two dogs, one hamster, and one rat mean values ofx between 2.419 and 2.903 were found. They lie within the range of 2.333 to 3.0 predicted by the analysis of Uylings (Bull. Math. Biol. 39, 501–519, 1977).     

The effects of proteolytic enzymes on the mechanical properties of adult human articular cartilage.

The effects of the lysosomal proteinase cathepsin D on the mechanical properties of adult human articular cartilage were examined in detail in 7 joints within the age range 21 to 72 years. The results of a preliminary study on the effects of the lysosomal proteinase cathepsin B1 and clostridial collagenase on the mechanical properties of cartilage are also presented. Cartilage which had been incubated with either cathepsin D or cathepsin B1 showed increased deformation in uniaxial compression perpendicular to the articular surface. The enzyme-treated cartilage also showed decreased tensile stiffness at low values of stress. This effect was more pronounced in specimens from the deeper zone of cartilage than in specimens from the superficial zone. It was also more pronounced in specimens which were aligned perpendicular to the predominant alignment of the collagen fibres in the superficial zone than in specimens which were parallel to the collagen fibres. At higher stresses the tensile stiffness of the treated cartilage was not significantly different from that of the untreated tissue. The tensile fracture stress of the cartilage was also not significantly reduced by the action of cathepsin D. In contrast to the effects observed with the cathepsins, the preliminary results obtained by incubating cartilage for 24 h with clostridial collagenase showed that both the tensile stiffness and the fracture stress were considerably lower than the corresponding values for the untreated tissue. Biochemical analysis of the incubation media, and the specimens, revealed that a large proportion of the proteoglycans was released from the cartilage by each of the three enzymes. The proportion of the total collagen which was released from the cartilage was different for each enzyme: cathepsin D released between 0 and 1.5 per cent, cathepsin B1 released between 2.3 and 4.3 per cent and collagenase released between 5.3 and 27.8 per cent of the collagen after 24 h.     

Mapping the zebrafish brain methylome using reduced representation bisulfite sequencing

Reduced representation bisulfite sequencing (RRBS) has been used to profile DNA methylation patterns in mammalian genomes such as human, mouse and rat. The methylome of the zebrafish, an important animal model, has not yet been characterized at base-pair resolution using RRBS. Therefore, we evaluated the technique of RRBS in this model organism by generating four single-nucleotide resolution DNA methylomes of adult zebrafish brain. We performed several simulations to show the distribution of fragments and enrichment of CpGs in different in silico reduced representation genomes of zebrafish. Four RRBS brain libraries generated 98 million sequenced reads and had higher frequencies of multiple mapping than equivalent human RRBS libraries. The zebrafish methylome indicates there is higher global DNA methylation in the zebrafish genome compared with its equivalent human methylome. This observation was confirmed by RRBS of zebrafish liver. High coverage CpG dinucleotides are enriched in CpG island shores more than in the CpG island core. We found that 45% of the mapped CpGs reside in gene bodies, and 7% in gene promoters. This analysis provides a roadmap for generating reproducible base-pair level methylomes for zebrafish using RRBS and our results provide the first evidence that RRBS is a suitable technique for global methylation analysis in zebrafish.     

Monitoring vegetation change caused by trampling: a study in the Cairngorms,Scotland

Summary

A study was made in the Cairngorms, Scotland to make recommendations for a monitoring scheme capable of detecting changes in the vegetation caused by recreational pressure following the development of a funicular railway. Four methods were used in field trials to assess percentage cover of plant species and gravel, rock and bare ground, where appropriate, in two vegetation types (open and closed). The methods used were visual estimates in 50 × 40 cm quadrats (Q), the mean of visual estimates in twenty 10 × 10 cm sub-quadrats of the 50 × 40 cm quadrats (Q₂₀), a modified point intercept method (RL) and photography. Variances between observers and between-quadrats were estimated for the different methods. The sampling design for detecting change was based on a model of variance, constructed from field trial data.

Between-observer and between-quadrat variances were related to mean percentage cover and approximated to a binomial distribution. The between-quadrat variance was larger than observer variance. The Q₂₀ method achieved appreciably better precision than the other methods. Analysis of half of the 10 × 10 cmsub-quadrats (1/2Q₂₀) selected in a checker board design achieved a relative efficiency of 78% compared with the Q₂₀. This result suggests that comparable precision to the Q₂₀ method could be achieved by choosing about 14 sub-quadrats in a larger quadrat, thus saving some time. Variation between quadrats also suggested that the Q₂₀ method was the one of choice for maximising precision. The precision of the photographic method was based on fewer data points, so is less accurate than other estimates.

Minimum sample sizes were estimated for detecting a 10% relative change of a species in open vegetation with 30% cover (i.e. a change from 30% to <27 or to >33% cover). With a 10 % Type II error rate and 5 % Type I error rate the minimum sample sizes were 47 quadrats for Q, 18 for Q ₂₀, 43 for RL, and 23 for the means of ten 10 × 10 cm sub-quadrats in open vegetation.

The most time-efficient field recording appeared to be the use of Q despite the required sample size being 2.6 times higher than that of Q₂₀. The far lower time requirement per quadrat, however, compensated for the higher numbers. The number of quadrats would depend on the specified change in percentage cover and on the statistical significance level used. For example, to detect a 10% absolute change in cover (i.e. from 30% to either <20 % or >40 % cover) at 95 % probability the net effective recording time is estimated at 5 h per vegetation type while to detect a 5 % change at 99 % probability would require c. 25 h. Larger samples may be required for other species or for species with a low initial cover.     

Regional Differences in Dynamic Cerebral Autoregulation in the Healthy Brain Assessed by Magnetic Resonance Imaging

A novel method is described for mapping dynamic cerebral blood flow autoregulation to assess autoregulatory efficiency throughout the brain, using magnetic resonance imaging (MRI). Global abnormalities in autoregulation occur in clinical conditions, including stroke and head injury, and are of prognostic significance. However, there is limited information about regional variations. A gradient-echo echo-planar pulse sequence was used to scan the brains of healthy subjects at a rate of 1 scan/second during a transient decrease in arterial blood pressure provoked by a sudden release of pressure in bilateral inflated thigh cuffs. The signal decrease and subsequent recovery were analyzed to provide an index of autoregulatory efficiency (MRARI). MRI time-series were successfully acquired and analyzed in eleven subjects. Autoregulatory efficiency was not uniform throughout the brain: white matter exhibited faster recovery than gray (MRARI = 0.702 vs. 0.672, p = 0.009) and the cerebral cortex exhibited faster recovery than the cerebellum (MRARI = 0.669 vs. 0.645, p = 0.016). However, there was no evidence for differences between different cortical regions. Differences in autoregulatory efficiency between white matter, gray matter and the cerebellum may be a result of differences in vessel density and vasodilation. The techniques described may have practical importance in detecting regional changes in autoregulation consequent to disease.     

Evidence of unique genotypes of beak and feather disease virus in southern Africa

Psittacine beak and feather disease (PBFD), caused by Beak and feather disease virus (BFDV), is the most significant infectious disease in psittacines. PBFD is thought to have originated in Australia but is now found worldwide; in Africa, it threatens the survival of the indigenous endangered Cape parrot and the vulnerable black-cheeked lovebird. We investigated the genetic diversity of putative BFDVs from southern Africa. Feathers and heparinized blood samples were collected from 27 birds representing 9 psittacine species, all showing clinical signs of PBFD. DNA extracted from these samples was used for PCR amplification of the putative BFDV coat protein (CP) gene. The nucleotide sequences of the CP genes of 19 unique BFDV isolates were determined and compared with the 24 previously described sequences of BFDV isolates from Australasia and America. Phylogenetic analysis revealed eight BFDV lineages, with the southern African isolates representing at least three distinctly unique genotypes; 10 complete genome sequences were determined, representing at least one of every distinct lineage. The nucleotide diversity of the southern African isolates was calculated to be 6.4% and is comparable to that found in Australia and New Zealand. BFDVs in southern Africa have, however, diverged substantially from viruses found in other parts of the world, as the average distance between the southern African isolates and BFDV isolates from Australia ranged from 8.3 to 10.8%. In addition to point mutations, recombination was found to contribute substantially to the level of genetic variation among BFDVs, with evidence of recombination in all but one of the genomes analyzed.