Spatial and temporal variations in the timing of leaf replacement in a Quercus cornelius‐mulleri population

Abstract. The phenology of spring leaf replacement was studied in a population of 46 evergreen scrub oaks (Quercus cornelius‐mulleri) at the edge of the Mojave Desert in each of five years over the period 1990–2001. The oaks occupied a site that spanned rocky slopes to sandy bajadas. The site receives variable annual rainfall (estimated 12‐yr average 195 mm; range in study years 67–706 mm). The spatial coordinates of all individuals were recorded, and in April, when leaf replacement was underway, individual replacement phenologies were assessed. Shrub sizes were recorded in three separate years, and in 2001 water potentials were measured. Individuals vary greatly in their timing of leaf replacement within years, and also between years. Many individuals with an early phenology one year are significantly later in the following year, and vice versa. While we detected weak influences on leaf replacement phenology due to shrub size, position within the site, and a genetic component, stronger influences were attributable to the phenology of the shrub in prior years, and to the phenology of neighbours within years. Neighbouring individuals that are close and/or large are significantly disparate in phenology, with one early and the other late. A potential mechanism of local resource depletion associated with costs to an early phenology is discussed.     

Rain forest composition and patterns of secondary succession in the Vava'u Island Group,Tonga

Abstract. The Vava'u island group, Tonga, comprises ca. 60 limestone islands on a single submarine platform overlain with rich soils derived from tephra deposits from nearby volcanic islands. The island group has moderate topographic relief (215 m) and is characterized by plateaus and steep cliffs. Humans settled in Tonga ca. 3000 yr ago and have exploited the flatter terrain for agriculture since that time. We conducted the first survey of forest composition in Vava'u, sampling remnant patches of late-successional forest as well as stands in various stages of secondary succession following agricultural abandonment. Plant species composition did not vary greatly with elevation over this short gradient, in contrast with patterns found on‘Eua, a higher island in Tonga. The most significant environmental gradient affecting species composition was coastal or maritime influence. However, the greatest variation in species composition and structure appeared to be related to species turnover during secondary succession, and we hypothesize a sequence of species replacements. Secondary forest begins to resemble late-successional forest in 30–50 yr in terms of structure and native species richness and therefore is of significant conservation value.     

Mediterranean pasture dynamics: the role of germination

Abstract. Meteorological patterns have a decisive influence on the inter-annual dynamics of therophyte pastures under Mediterranean climatic conditions. The germination behaviour of annual pasture species was studied by subjecting two collections of seeds taken from plants and soil-seed banks to two phytotron-simulated weather patterns: early and late autumn rains. Species from these pastures were arranged along a gradient of sensitivity to temperature on the arrival of the first persistent rain. This sensitivity was manifested in both the total germination success of the species and the germination time profile. The different germination patterns of the species can provide competitive advantages depending on the autumn weather conditions.     

Molecular cloning of the ADE1 gene of Saccharomyces cerevisiae and stability of the transformants

Plasmid YEp(ADE1)1a, containing a 2.7-kb Sau3A fragment of Saccharomyces cerevisiae DNA inserted at the BamHI site of the yeast shuttle vector pBTI-1 (Morris et al., 1981), results in high frequency, unstable transformation of ade1 yeast strains. A second plasmid, YRp(ADE1)2, containing adjacent 0.5-kb and 3.0-kb BamHI fragments in pBR322 gave three types of yeast transformants: (1) transformants carrying extrachromosomal copies of the plasmid which indicate the presence of a functional ars sequence, (2) transformants indistinguishable from ade1 strains by hybridization analyis, and (3) a transformant carrying a multimeric form of YRp(ADE1)2. Cells transformed with either of the plasmids are free of the red pigment characteristic of ade1 mutants and indicate potential for direct colour-based selection of yeast transformants using ADE1 plasmids.     

Occult hepatitis C virus elicits mitochondrial oxidative stress in lymphocytes and triggers PI3-kinase-mediated DNA damage response

Occult hepatitis C viral infection (OHCI) is a newly reported pathological entity associated with increased risk of developing hepatocellular carcinoma and lymphoproliferative disorders. Although hepatocytes are the primary sites of viral replication, hepatitis C virus is potentially lymphotropic, invading and propagating in cells of the immune system. Lymphocytes, the extrahepatic viral reservoirs, are differentially implicated in the occult and the active forms of the disease. This study aimed to elucidate the implications of mitochondrial oxidative stress on the immune pathophysiological mechanisms of OHCI. We herein report that OHCI induces mitochondrial oxidative stress, leading to DNA double-strand breaks and elicitation of a phosphoinositol 3-kinase-mediated cellular response in peripheral blood lymphocytes. Compared to controls, OHCI subjects showed higher accumulation of pATM, pATR, γH2AX, and p-p53, along with active recruitment of repair proteins (Mre11, Rad50, and Nbs1) and altered mitochondrial DNA content. Increased mitochondrial membrane depolarization and circulating nucleosome levels along with chromatid-type aberrations and decreased T-cell proliferative index observed in the OHCI group further indicated that this damage might lead to Bax-triggered mitochondria-mediated cellular apoptosis. Together our results provide the mechanistic underpinnings of mitochondrial dysfunction in OHCI, a previously unknown paradigm, for explaining the immune pathogenesis in a redox-dependent manner.     

Classification of peatland vegetation in Atlantic Canada

Abstract. The peatlands of Atlantic Canada are classified in four plant alliances, consisting of 10 plant associations. The four plant alliances comprise the dry bog communities (Kalmio-Cladonion Wells 1981), wet bog communities (Scirpo-Sphagnion Wells 1981), hummock and ridge communities of slope and string fens (Betulo-Sphagnion Wells all. nov.), and poor, intermediate and rich fen plant communities (Scirpo-Myricion Wells 1981). Distribution maps are presented for relevés in each of the 10 associations. Based on species distributions, floristic regions are defined for peatlands in Atlantic Canada. Nutritional characteristics are also described for each plant association. pH and total soil concentrations of calcium, nitrogen and iron proved reliable in separating bog from fen. A boundary between ombrotrophic peatlands and minerotrophic peatlands is suggested, based on a soil pH of 4.0, total soil concentrations of 3.0 mg g^?1 Ca, 4.0 mg g^?1 Fe, 13.0 mg g^?1 N and a Ca/Mg ratio of 2.5. Comparisons between the syntaxa for peatlands in Atlantic Canada and those in Europe are discussed for higher taxa. The possibility of establishing a new order (Chamaedaphno-Scirpetalia Wells ord. nov.) for peatlands in Atlantic Canada is also discussed.     

Do rivers function as corridors for plant dispersal?

Abstract. We evaluated the importance of dispersal for species frequencies and distribution by comparing dispersal properties of vascular plant species with their frequencies along river banks. We assumed that species with long-floating seeds would be more frequent than species with short-floating seeds. We compiled data on frequencies of vascular plants and their dispersal properties from ten rivers in northern Sweden and compared these with boreal forests and grasslands in the same region. In all rivers, but in none of the reference areas, there was a positive relationship between floating capacity and frequency of species. A comparison of floating capacity between species with and without certain dispersal devices showed that seeds of vegetatively dispersed species had higher floating capacities than other seeds. For other dispersal categories (animal and wind dispersal), floating time did not differ from contrast groups. The results indicate that water dispersal has a certain role in structuring the riparian flora, and provide a basis for explaining species distribution patterns from dispersal characteristics. They also suggest that continuous river corridors are important for maintaining regional biodiversity.     

Effects of Variations in Glutamic Acid Decarboxylase Activity on Acute Oxygen Poisoning

Abstract— A study was made to test the influence of rapid variations in glutamic acid decarboxylase (GAD) activity on the susceptibility of rats to hyperbaric oxygen (HBO). GAD was inhibited by the convulsant drug unsymmetrical dimethylhydrazine (UDMH) and reactivated by pyridoxine (PYR) after onset of convulsive activity. There was a relatively long induction period after UDMH injection until the onset of convulsions and the predictable interictal periods between successive periodic convulsions made it possible to study the impact of variations in GAD activity on survival rates, suspectibility to HBO and brain glycogen levels in a time sequence after UDMH administration. The experiments showed that UDMH interferes with aerobic metabolism in brain in such a way that profound alterations in resistance to acute oxygen poisoning resulted. An accumulation of substrate proximal to the enzyme block is assumed to develop during UDMH poisoning. The protective effect against HBO toxicity that was achieved after reactivation of GAD by PYR injection, as well as the rapid re-establishment of glycogen levels, is believed to speak in favour of this hypothesis.     

Factors controlling vegetation change in long-term experiments designed to restore heathland in Breckland,UK

Abstract. This paper describes the vegetation change in an 18-year experiment designed to test a range of control of Pteridium aquilinum (Pteridium) and heathland restoration treatments; cutting, asulam application and Calluna vulgar is seeding, in a range of combinations at Cavenham Heath in Breckland, UK between 1978 and 1996. Vegetation change was recorded in two Phases; in Phase I (1978-1986) species biomass was sampled and in Phase II (1986-1996) cover was measured. Initially, Calluna establishment was good in some treatments, especially where Calluna seed was added and Pteridium was controlled. Other plots developed either a grass-heath flora dominated by Agrostis capillaris, Deschampsia flexuosa, Dicranum scoparium, Festuca ovina and Rumex acetosella or were dominated by clonal species such as Calamagrostis epigejos or Carex arenaria. An unconstrained ordination showed significant vegetation change through time and that several treatments influenced the vegetation, especially those involving asulam application. When variation partitioning with constrained ordination was used a different explanation emerged. In Phase I the most important factors were the management treatments applied, elapsed time and spatial factors, with little overlap. In Phase II, elapsed time became irrelevant because the variation time explained overlapped that which could be explained by other variables. The most important of these were management treatments, spatial effects, weather, the amount of bare ground caused by disturbance and Pteridium litter cover (an index of Pteridium recovery). The implications of these results in interpreting vegetation change are discussed.     

Molecular Forms of Acetylcholinesterase in Pineal Cell and Sympathetic Neuronal Cultures

Abstract The activities of the various molecular forms of acetylcholinesterase (AChE) were measured in monolayer cultures of neonatal rat pineal cells grown alone and in co-culture with sympathetic neurons. AChE forms characterized by sedimentation coefficients of 4S, 6.5S, and 10S were found in the neuronal and pineal cultures, as well as in the co-cultures. The 16S AChE form was found only in the neuronal cultures. Total AChE activity increased with culture age in the co-cultures, but it decreased in pineal cells cultured alone. The low level of activity present in the neuronal cultures did not change markedly over the 27-day culture period. These results, which show bidirectional neuron-pineal cell effects, suggest that AChE molecular forms may be important markers to study the mechanisms underlying neuron-target cell interaction in the developing sympathetic nervous system.