On blocking rules for the bootstrap with dependent data

We address the issue of optimal block choice in applicationsof the block bootstrap to dependent data. It is shown that optimalblock size depends significantly on context, being equal ton^1/3, n^1/4 and n^1/5 in the cases of variance or bias estimation,estimation of a onesided distribution function, and estimationof a two-sided distribution function, respectively. A clearintuitive explanation of this phenomenon is given, togetherwith outlines of theoretical arguments in specific cases. Itis shown that these orders of magnitude of block sizes can beused to produce a simple, practical rule for selecting blocksize empirically. That technique is explored numerically.     

OPERATION OF THE PURINE NUCLEOTIDE CYCLE IN ANIMAL TISSUES

1. The operation of the purine nucleotide cycle, consisting of the enzymes adenylate deaminase (E.C. 3.5.4.6), adenylosuccinate synthetase (E.C. 6.3.4.4) and adenylosuccinate lyase (E.C. 4.3.2.2), has been reviewed with reference to its metabolic function in animal tissues.
2. Abundant evidence, both from in vitro and in vivo studies, suggests that the purine nucleotide cycle serves to stabilize the adenylate 'energy charge' (or 'phosphorylation potential') in the cytoplasm of vertebrate cells during a temporary imbalance between ATP-consumption and ATP-production. This stabilization, however, is absent or much less efficient in tissues of invertebrates.
3. The hypothesis that AMP-deaminase is involved in the regulation of glycolysis is not supported by recent work. In a variety of cell types, including skeletal muscle and blood platelets, blocking of AMP-deaminase activity (due to a genetic defect or to pharmacological inhibition) is without effect on the glycolytic rate. Detailed kinetic and histochemical analysis of energy metabolism shows lack of correlation between AMP-deaminase activity and glycolysis in skeletal muscle during exercise.
4. The purine nucleotide cycle appears to control the level of citric acid cycle intermediates in skeletal muscle. Pharmacological inhibition of adenylosuccinate lyase or adenylosuccinate synthetase leads to a reduced availability of four-carbon 'sparker' molecules to the Krebs cycle with a concomitant impairment of aerobic energy production during muscular work.
5. The cycle appears to be a major pathway for amino acid deamination in skeletal muscle and brain of vertebrates, but not in kidney or liver.     

Characterization of polymorphic microsatellite markers for the Carnaby's cockatoo (Calyptorhynchus latirostris) and related black cockatoo species

Microsatellite loci were isolated from Carnaby's black cockatoo (Calyptorhynchus latirostris: Aves), a highly valued, endangered, and endemic species of bird from Western Australia. This study describes three dinucleotide and one tetranucleotide microsatellite loci for which the primers produced clear and polymorphic amplification patterns with between two and nine alleles and moderate levels of variability. Two additional dinucleotide markers which were monomorphic in the Carnaby's cockatoo were able to amplify and were polymorphic in two other species of black cockatoo, greatly increasing the utility of these markers.     

Cyanide-Resistant Root Respiration and Tap Root Formation in Two Subspecies of Hypochaeris radicata

Root respiration of the tap root forming species Hypochaeris radicata L. was measured during tap root formation. A comparison was made of two subspecies: H. radicata L. ssp. radicata L., a subspecies from relatively rich soils, and H. radicata L. ssp. ericetorum Van Soest, a subspecies from poor acidic soils. Root respiration was high and to a large extent inhibited by hydroxamic acid (SHAM) before the start of the tap root formation, indicating a high activity of an alternative non-phosphorylative electron transport chain. The rate of root respiration was much lower and less sensitive to SHAM when a considerable tap root was present. However, root respiration was also cyanide-resistant when a tap root was present, indicating that the alternative pathway was still present. A decreased rate of root respiration coincided with an increase of the content of storage carbohydrates, mainly in the tap root. The level of reducing sugars was constant throughout the experimental period, and it was concluded that the activity of the alternative oxidative pathway was significant in oxidation of sugars that could not be utilized for purposes like energy production, the formation of intermediates for growth or for storage. Root respiration decreased after the formation of a tap root. This decrease could neither be attributed to a gradual disappearance of the alternative chain, nor to a decreased level of reducing sugars. No differences in respiratory metabolism between the two subspecies have been observed, suggesting that a high activity of the alternative oxidative pathway is not significant in adaptation of the present two subspecies to relatively nutrient-rich or poor soils.     

Occurrence of a Cytokinin Glucoside in the Leaves and in Honeydew of Salix babylonica

Honeydew and leaf extracts from Salix babylonica indicate that large quantities of cytokinin are present in the leaves and are transported through the phloem of this plant during late autumn. The active compound in the extracts could be hydrolysed with β-glucosidase, whereafter it showed the same chromatographic behaviour as zeatin. It is proposed that cytokinins in the leaves are converted to the glucoside and then redistributed to the rest of the plant organs where it is stored.     

Long-term changes of diatoms and chemistry in headwater streams polluted by atmospheric deposition of sulphur and nitrogen compounds

1. Samples for the analysis of attached diatoms and surface water chemistry were taken at thirty-five stations in sixteen soft-water streams in the Netherlands during autumn 1990. Most were located in pine forest and heathland catchments, fed by deep groundwater (median residence time 87 years), with no direct influence of agricultural or urban drainage water. 2. The chemical data from sixteen stations were compared with data collected in 1974 and 1981. There were no significant increases in pH (6.3 in 1974, 6–4 in 1990) or in sulphate (200 mmol m^?3 in 1974, 229 mmol m^?3 in 1990). Over the same period nitrate increased significantly from 17 to 158 mmol m^?3, while alkalinity decreased significantly from 355 to 251 meq m^?3. 3. The most important correlates with the distribution of diatoms, as revealed by canonical correspondence analysis, were pH, nitrate, cross-sectional area of the stream and the Ca/(Ca + Cl) ratio. 4. Diatom assemblages of upstream stations indicated more acid conditions than those of downstream stations. Also there was considerable variation in the diatom assemblages of different habitats, 5. A diatom-pH transfer function was developed using the weighted-averaging method. The function was applied to comparable pairs of samples which were collected in 1974 and 1990 at ten stations. There was a significant decrease in the median diatom-inferred pH from 6.78 in 1974 to 6.55 in 1990. 6. The diatom assemblages are diverse and contain a high proportion of filamentous diatoms, particularly Aulacoseira crenulata and A. alpigena, which are rare in Western Europe. This is a response to the low current velocity (median 5 cm^?1) and the relatively constant deep groundwater discharge.     

The Structure and Development of the Reproductive Organs and Carposporophyte in two British Species of Gelidium

The structure and development of the reproductive organs andcarposporophyte are described for two British species of Gelidium,G. latifolium (Grev.) Born. & Thur. and G. pulchellum (Turn.)Kütz. The gonimoblast does not develop directly from theunchanged carpogonium, as was thought by Kylin, but a swollenmultinucleate cell of irregular outline is formed first, eitherfrom the carpogonium alone, or by the fusion of the carpogoniumand certain neighbouring cells; the gonimoblast develops fromlong, non-septate processes of this multi-nucleate cell. Thesignificance of the fusion of the carpogonium and certain vegetativecells is discussed in relation to the various definitions ofthe auxiliary cell which have been proposed. It is concludedthat an auxiliary cell does not occur in Gelidium.