Effects of spring and autumn fires on the composition of Chionochloa rigida tussock grassland,New Zealand

Two areas of Chionochloa rigida tussock grassland on Flagstaff Hill were burnt in autumn and spring 1976, respectively. Plant species cover and frequency were recorded in 1977 and 1985. Initially, plant cover and frequency were lower, and the area of bare ground was greater, on the autumn burnt site. After nine years, cover and frequency values were similar for most species, and bare ground was rare, on both sites. Over this period, recovery in size of indigenous tussock-forming physiognomic dominants resulted in suppression of intertussock sub-shrubs, herbs and grasses that were initially favoured by reduction of competition after fire. Plant species most tolerant of fire have features that protect the meristem, for instance an underground perennating organ or dense tillering.     

Antigenic mapping of a human λ light chain: Correlation with three dimensional structure

Although the amino acid sequence and three-dimensional structure of human immunoglobulin light chains have been known for more than 15 years, the location of antigenic markers characteristic of chains has not been determined. Here, we use a set of synthetic overlapping peptides to completely model the sequence of the chain Mcg and test these for the binding or rabbit and goat antisera specific for chain determinants. We assess peptide contributions to -antigenic reactivity and also to identify a portion of C-region where conformational factors contribute to the antigenicity. Specific determinants occur both in the constant and variable (first and third framework) domains of the molecule. The fourth framework of the variable region, a segment specified by the joining gene, is also recognized and cross-reacts antigenically with the homologous region of T cell receptor chains. Major specific determinants are localized in the N- and C-terminal segments, which are linear and devoid of major conformational folding. Other segments that are strongly antigenic, such as the third framework of the V region (residue 78–93) and a segment of the constant region (residues 177–192), show strong conformational dependence in antigenicity.     

Separation and analysis of the glycoform populations of ribonuclease B using capillary electrophoresis

The development of methods to separate, analyse and monitor changes in glycoform populations is essential if a more detailed understanding of the structure, function and processing of glycoproteins is to emerge. In this study, intact ribonuclease B was resolved by borate capillary electrophoresis into five populations according to the particular oligomnnose structure associated with each glycoform. The relative proportions of these populations are correlated with the percentages obtained indirectly by analysis of the hydrazine released oligosaccharides using Bio-Gel P-4 gel filtration, matrix assisted laser desorption mass spectrometry and high performance anion exchange chromatography. Alterations in the composition of the glycoform populations during digestion of ribonuclease B withA. saitoi (1–2)mannosidase were monitored by capillary electrophoresis (CE). Digestion of the free oligosaccharides under the same conditions, monitored by anion exchange chromatography, revealed a difference in rate, allowing some insight into the role of the protein during oligosaccharide processing. In conjunction with other methods, this novel application of CE may prove a useful addition to the techniques available for the study of glycoform populations.     

The effect of dissolved oxygen on the growth of young-of-the-year winter flounder,Pseudopleuronectes americanus

Synopsis The effects of constant and diurnally fluctuating levels of dissolved oxygen on the growth of young-of-the-year winter flounder,Pseudopleuronectes americanus, were examined under controlled laboratory conditions. Fish were exposed for either 10 or 11 weeks to constant levels of 6.7 (high) and 2.2 (low) mg l^–1, and a diurnal fluctuation, ranging from 2.5 to 6.4 mg 0₂l^–1. Growth rates, calculated for both standard length and weight, for fish exposed to low and diurnally fluctuating levels were significantly reduced (p < 0.001) as compared to those for fish exposed to the high level. Growth rates of fish exposed to the high level were over twice those of fish held under low oxygen conditions. Under fluctuating conditions, fish grew at intermediate rates. Following these exposures, all fish were subsequently held at 7.2 mg Oz l^–1 for five weeks. Growth rates increased over two and a half times for fish previously exposed to the low oxygen level and were significantly (p < 0.001) higher than for the other two groups.     

Glutathione production in copper-deficient isolated rat hepatocytes.

Dietary copper deficiency has been shown to reduce copper-dependent superoxide dismutase (SOD) activity and to increase lipid peroxidation in rats. Circulating reduced glutathione (GSH) concentrations are elevated in copper-deficient (CuD) rats, which suggests an increased GSH synthesis or decreased degradation, perhaps as an adaptation to the oxidative stress of copper deficiency. GSH synthesis was examined in isolated hepatocytes from CuD rats. Isolated hepatocytes were prepared by collagenase perfusion and incubated in Krebs-Henseleit bicarbonate buffer, pH 7.4, 10 mM glucose, 2.5 mM Ca2+ in the presence and absence of 1.0 mM buthionine sulfoximine (BSO), a specific inhibitor of GSH synthesis. Cell viability was assessed by trypan blue exclusion. GSH and oxidized glutathione (GSSG) were measured by the glutathione reductase recycling assay. Copper deficiency depressed hepatocyte Cu by greater than 90% and increased intracellular GSH by 41-117% over the 3-h incubation, with a two- to threefold increase in the rate of intracellular GSH synthesis. Intracellular GSSG values were minimally influenced by CuD, with a constant mol% GSSG. Extracellular total glutathione (GSH + 2GSSG) synthesis was increased by approximately 33%. Both intracellular GSH and extracellular total glutathione synthesis were inhibited by BSO. The pattern of food consumption in CuD rats, meal fed versus ad libitum fed, had no effect on glutathione synthesis. The results indicate an increased hepatic GSH synthesis as a response to dietary copper deficiency and suggest an interrelationship between the essential nutrients involved in oxyradical metabolism.     

Herpes simplex virus type 1-specific cytotoxic T lymphocytes recognize immediate-early protein ICP27.

The identity of herpes simplex virus type 1 (HSV-1) antigens that serve as targets for cytotoxic T lymphocytes (CTL) and their ability to induce protective immunity remain uncertain. In this article, we report the identification of the immediate-early protein ICP27 as a CTL antigen in H-2d mice but not in H-2k or H-2b mice. Calculation of the frequencies of H-2d-restricted virus-specific CTL demonstrated that approximately one-fourth of the total HSV-1-specific response was directed against ICP27. To define the location of this CTL epitope, four truncated derivatives of the ICP27 gene which place the epitope in a 217-amino-acid region (amino acids 189 to 406) near the central portion of the protein were constructed. Mice immunized with ICP27 were able both to induce HSV-1-specific CTL and to survive a lethal intraperitoneal challenge with virulent HSV-1. However, neither appreciable antibody nor delayed-type hypersensitivity responses were induced in immunized mice, and they were also unable to clear a local epithelial virus challenge. It appears that ICP27, although capable of inducing several aspects of the immune response, is by itself unable to provide complete immunity.     

A discrete-time model with vaccination for a measles epidemic.

A discrete-time, age-independent SIR-type epidemic model is formulated and analyzed. The effects of vaccination are also included in the model. Three mathematically important properties are verified for the model: solutions are nonnegative, the population size is time-invariant, and the epidemic concludes with all individuals either remaining susceptible or becoming immune (a property typical of SIR models). The model is applied to a measles epidemic on a university campus. The simulated results are in good agreement with the actual data if it is assumed that the population mixes nonhomogeneously. The results of the simulations indicate that a rate of immunity greater than 98% may be required to prevent an epidemic in a university population. The model has applications to other contagious diseases of SIR type. Furthermore, the simulated results of the model can easily be compared to data, and the effects of a vaccination program can be examined.     

Determination for inflorescence development is a stable state,separable from determination for flower development in Pisum sativum L. buds

Terminal meristems of Pisum sativum (garden pea) transit from vegetative to inflorescence development, and begin producing floral axillary meristems. Determination for inflorescence development was assessed by culturing excised buds and meristems. The first node of floral initiation (NFI) for bud expiants developing in culture and for adventitious shoots forming on cultured meristems was compared with the NFI of intact control buds. When terminal buds having eight leaf primordia were excised from plants of different ages (i.e., number of unfolded leaves) and cultured on 6-benzylaminopurine and kinetin-supplemented medium, the NFI was a function of the age of the source plant. By age 3, all terminal buds were determined for inflorescence development. Determination occurred at least eight nodes before the first axillary flower was initiated. Thus, the axillary meristems contributing to the inflorescence had not formed at the time the bud was explanted. Similar results were obtained for cultured axillary buds. In addition, meristems excised without leaf primordia from axillary buds three nodes above the cotyledons of age-3 plants gave rise to adventitious buds with an NFI of 8.3 ±0.3 nodes. In contrast seed-derived plants had an NFI of 16.5 ±0.2. Thus cells within the meristem were determined for inflorescence development. These findings indicate that determination for inflorescence development in P. sativum is a stable developmental state, separable from determination for flower development, and occurring prior to initiation of the inflorescence at the level of meristems.