Crown alterations induced by decline: a study of relationships between growth rate and crown morphology in beech (Fagus sylvatica L.)

One of the first symptoms expressed by declining trees is reduced growth in stem diameter and length increment. The possibility of a relationship between length increment and crown thinning in beech (Fagus sylvatica L.) was investigated by developing a computer model to simulate first order branching patterns of the apical 2 m of monopodially branching beech trees, 70–100 years old, for a range of length increment rates. The model was based on values for branching angle, main axis and branch length increment, number of branches produced per year and branch mortality rates for six healthy and declining trees. Shoot growth rates in the apical 2 m of the sample trees ranged from about 5 cm/year (decline class 3) to 43 cm/ year (healthy). Simulations of branching patterns in the apical 2 m of trees growing at different rates indicated that, when growth rate exceeded about 20 cm/year, total first order branch length and area explored were independent of growth rate. When growth rates fell below this value there was a reduction in total area explored and first order branch length due primarily to the formation of fewer branches. More acute branching angles contributed to a reduction in the area explored. Growth rate-related crown thinning could increase the risk of bark necrosis and secondary pathogen infection during dry and/or hot spells.     

Rapid determination of vapA/vapB genotype in Rhodococcus equi using a differential polymerase chain reaction method

Rhodococcus equi is a facultative pathogen of foals. Infection causes an often fatal pulmonary pneumonia. The organism has also been isolated from pigs, cattle, humans and the environment. Equine virulence has a high positive correlation with the expression of a 17.4 kD polypeptide of unknown function, VapA, the product of the plasmid-encoded vapA gene. More recently an isogene of vapA, referred to as vapB and encoding an 18.2 kDa polypeptide, has been identified among pig and human isolates. The two genes share > 80% sequence identity, yet their host strains apparently exhibit different pathogenicity profiles (for example by reference to virulence in mouse model system and host specificity). In this study, a polymerase chain reaction (PCR) technique was developed that permits the selective amplification of vapA and vapB. Using this technique the distribution of the two genes among 35 randomly selected isolates of Rhodococcus equi from various animal and environmental sources was determined. Using this technique the genotype of each isolate could be unambiguously assigned as vapA+, vapB+ or vap- (i.e., scoring negative for both vapA and vapB). No isolate scored positive for both vapA and vapB. 100% of equine isolates scored vapA+, confirming the status of vapA as a reliable marker of equine virulence. All three genotypes were found among human isolates; porcine isolates scored either vapB+ or vap- and no vapA+ isolates were present in this sample. Rigorous statistical analysis using the Fisher Exact test confirmed that the high frequency of vapA+ among equine isolates is significant; however the sample size was too small to draw statistically significant conclusions regarding the distribution of genotypes among within other animal groups.     

DNA sequence changes in mutations induced by ultraviolet light in the gpt gene on the chromosome of Escherichia coli uvr+ and urvA cells

Summary Sequence changes in mutations induced by ultraviolet light are reported for the chromosomal Escherichia coli gpt gene in almost isogenic E. coli uvr ⁺ and excision-deficient uvrA cells. Differences between the mutagenic spectra are ascribed to preferential removal of photoproducts in the transcribed strand by excision repair in uvr ⁺ cells. This conclusion is confirmed by analysis of published results for genes in both uvr ⁺ and uvr ^– cells, showing a similar selective removal of mutagenic products from the transcribed strand of the E. coli lacI gene and of the lambda phage cl repressor gene. Comparison of these data with published results for ultraviolet mutagenesis of gpt on a chromosome in Chinese hamster ovary cells showed that a mutagenic hot spot in mammalian cells is not present in E. coli; the possibility is suggested that the hot spot might arise from localized lack of excision repair. Otherwise, mutagenesis in hamster cells appeared similar to that in E. coli uvr ⁺ cells, except there appears to be a smaller fraction of single-base additions and deletions (frameshifts) in mammalian than in bacterial cells. Phenotypes of 6-thioguanine-resistant E. coli showed there is a gene (or genes) other than gpt involved in the utilization of thioguanine by bacteria.     

Microtubule nucleation at non-spindle pole body microtubule-organizing centers requires fission yeast centrosomin-related protein mod20p

BACKGROUND: Many types of differentiated eukaryotic cells display microtubule distributions consistent with nucleation from noncentrosomal intracellular microtubule organizing centers (MTOCs), although such structures remain poorly characterized. In fission yeast, two types of MTOCs exist in addition to the spindle pole body, the yeast centrosome equivalent. These are the equatorial MTOC, which nucleates microtubules from the cell division site at the end of mitosis, and interphase MTOCs, which nucleate microtubules from multiple sites near the cell nucleus during interphase. RESULTS: From an insertional mutagenesis screen we identified a novel gene, mod20+, which is required for microtubule nucleation from non-spindle pole body MTOCs in fission yeast. Mod20p is not required for intranuclear mitotic spindle assembly, although it is required for cytoplasmic astral microtubule growth during mitosis. Mod20p localizes to MTOCs throughout the cell cycle and is also dynamically distributed along microtubules themselves. We find that mod20p is required for the localization of components of the gamma-tubulin complex to non-spindle pole body MTOCs and physically interacts with the gamma-tubulin complex in vivo. Database searches reveal a family of eukaryotic proteins distantly related to mod20p; these are found in organisms ranging from fungi to mammals and include Drosophila centrosomin. CONCLUSIONS: Mod20p appears to act by recruiting components of the gamma-tubulin complex to non-spindle pole body MTOCs. The identification of mod20p-related proteins in higher eukaryotes suggests that this may represent a general mechanism for the organization of noncentrosomal MTOCs in eukaryotic cells.     

Measuring blood pressure in the elderly: does atrial fibrillation increase observer variability?

OBJECTIVE--To compare the interobserver and intraobserver variability of blood pressure measurements in geriatric patients in atrial fibrillation and in sinus rhythm. DESIGN--Prospective assessment of blood pressure measurements carried out in random order in two groups of elderly patients by five doctors unaware of the aims of the study. SETTING--Acute assessment wards for geriatric medicine, Cardiff Royal Infirmary. PATIENTS--50 Elderly patients in sinus rhythm and 50 in atrial fibrillation. MAIN OUTCOME MEASURES--Interobserver and intraobserver variability of blood pressure measurements in the two groups expressed as the coefficient of variability and compared by the Mann-Whitney U test. RESULTS--Interobserver variability was significantly greater in the patients with atrial fibrillation for both systolic and diastolic pressures. Intraobserver variability was significantly greater in the atrial fibrillation group for diastolic pressures but the difference was not significant for systolic pressures. These differences were not related to pulse rate, age, or level of blood pressure. CONCLUSIONS--The findings suggest that in the presence of atrial fibrillation physicians'' interpretations of Korotkoff sounds are less uniform, which may have important clinical implications. Possibly a standardised methodology may overcome this problem.     

Minisatellite DNA profiling detects lineages and parentage in the endangered kakapo (Strigops habroptilus) despite low microsatellite DNA variation

An important goal of the conservationmanagement program of the critically endangeredground parrot, the New Zealand kakapo (Strigops habroptilus) is the determination ofparentage and levels of genetic diversitywithin the remaining population. Our previousmicrosatellite DNA studies have shown that allindividuals of this species except one arehomozygous at seven loci examined. Incontrast, we now show that a minisatellite DNAanalysis of kakapo provides sufficientvariation to conduct paternity analyses anddetect heterogeneity within the 86 livingkakapo. The sole remaining Fiordland kakapo,Richard Henry, is shown to be geneticallydivergent from individuals originating from theonly other remaining population on StewartIsland, suggesting that two lineages of kakapoare present in the extant population. This hasparticular significance for the conservationmanagement goal of maintenance of the maximumgenetic diversity in the species as a whole. The example of the kakapo illustrates thatminisatellite DNA markers can be useful incases where microsatellite DNA fails to showsufficient variation.     

Modulation of Anopheles gambiae Epsilon glutathione transferase activity by plant natural products in vitro

Elevated glutathione transferase (GST) E2 activity is associated with DDT resistance in the mosquito Anopheles gambiae. The search for chemomodulators that inhibit the function of AgGSTE2 would enhance the insecticidal activity of DDT. Therefore, we examined the interaction of novel natural plant products with heterologously expressed An. gambiae GSTE 2 in vitro. Five of the ten compounds, epiphyllocoumarin (Tral-1), knipholone anthrone, isofuranonaphthoquinones (Mr 13/2, Mr13/4) and the polyprenylated benzophenone (GG1) were shown to be potent inhibitors of AgGSTE2 with IC(50) values of 1.5 microM, 3.5 microM, 4 microM, 4.3 microM and 4.8 microM respectively. Non-competitive inhibition was obtained for Tral 1 and GG1 with regards to GSH (K(i) of 0.24 microM and 0.14 microM respectively). Competitive inhibition for Tral1 was obtained with CDNB (K(i) = 0.4 microM) whilst GG1 produced mixed type of inhibition. The K(i) and K(i)' for GSH for Tral-1 and GG1 were 0.2 microM and 0.1 microM respectively. These results suggest that the novel natural plant products, particularly Tral-1, represent potent AgGSTE2 in vitro inhibitors.     

Is red blood cell survival limited by the activity of a critical enzyme?

Erythrocyte glutathione reductase is responsible for generating reduced glutathione, which has been implicated in maintaining the integrity of the red blood cell.Erythrocytes from peripheral blood were separated into fractions of increasing age and the activity of glutathione reductase and aspartate amino transferase determined in each fraction.The age-related decline in activity of both enzymes was confirmed, but with detailed resolution of the cells by age a significant secondary rise in only glutathione reductase activity was found in very old cells. As red blood cells from the same cohort survive in the circulation for varying periods they must vary in some way from one another. It is postulated that glutathione reductase is a critical enzyme which limits erythrocyte survival and that the rate of decline in activity varies from cell to cell. A simple mathematical model based on this postulate accounted quantitatively for both the pattern of glutathione reductase activity and the erythrocyte survival curve. In addition, a simplified model of the passage of erythrocytes through the circulation was designed and run. The predicted erythrocyte survival curve and pattern of glutathione reductase activity were very similar to observed patterns. This model may be useful in other situations where a finite resource is degraded at different rates by random passages through different pathways.