Growth enhancement of the macrophyte Ceratophyllum demersum in the presence of the snail Planorbis planorbis: the effect of grazing and chemical conditioning

• 1 The effects of epiphyton grazing and nutrient recycling by the freshwater snail Planorbis planorbis on the growth of the macrophyte Ceratophyllum demersum were examined in laboratory experiments.
• 2 Ceratophyllum plants grown in the presence of snails, or in water chemically conditioned by snails, were significantly longer, had more healthy nodes of leaves, and more growing tips than Ceratophyllum plants grown in isolation. There were no significant differences between the growth of plants that were grazed by snails, and those plants which received water chemically conditioned by snails.
• 3 Adult P. planorbis released 3.74 × 10^?4μg phosphate, 23.9 × 10^?4μg nitrate, 4.38 × 10^?4μg ammonia, and 0.79 × 10^?4μg of urea mg^?1 wet weight of snail h^?1. Measurements of these chemicals in the experimental systems suggested that ammonia was an important nutrient in stimulating the growth of Ceratophyllum.
• 4 Removal of epiphyton by grazing snails significantly prolonged the life of individual Ceratophyllum leaves compared to ungrazed leaves.

     

Electrophoretic Karyotype and Linkage Groups of the Amoeboflagellate Naegleria gruberi

ABSTRACT. We have constructed a molecular karyotype for two strains of Naegleria gruberi using pulsed field gel electrophoresis. Each strain has about 23 chromosomes, considerably more than any previous estimate. These chromosomes range in size from 400 kilobasepairs to over 2,000 kilobasepairs. In Naegleria , construction of the DNA karyotype depends on assessment of the anomalous electrophoretic mobility of the circular ribosomal RNA genes. We have determined the chromosomal locations of an identified unique gene (flagellar calmodulin) and four identified multigene families (α- and β-tubulin, actin, ubiquitin), as well as three differentially expressed genes of unknown functions. The ca. 12 actin genes are dispersed over at least seven chromosomes, whereas the majority of the more than eight α-tubulin genes are confined to a single chromosome. The ubiquitin genes are found on five chromosomes in one strain and seven in the other and the β-tubulin genes are on three or four. Our observations provide a foundation for molecular genetic studies in this organism.     

The size and composition of soil seed-banks in remnant patches of three structural rainforest types in North Queensland

The size and species composition of the soil seed-bank in a remnant patch of each of three structurally and floristically distinct rainforests (Complex Mesophyll Vine Forest, Complex Notophyll Vine Forest and Semi-Evergreen Vine Thicket) were assessed. Seeds of 94 species germinated from 12 surface soil samples collected from each site. All three seed-banks were composed mostly of herbs characteristic of roadsides and agricultural land, and pioneer rainforest trees and shrubs. Agglomerative classifications indicated that the seed-bank samples from each rainforest remnant had a characteristic species composition and could be distinguished reliably from seed-bank samples drawn from other sites. Seeds of species present in the standing forest were poorly represented in the seed-banks except for one long-lived pioneer tree, Dendrocnide photinophylla, at one site. The seed-bank from the seasonally dry vine thicket was significantly larger (4000 seeds m^-2) than those from the two moister sites (400–600 seeds m^-2, contained more seeds of roadside and agricultural herbs, and fewer seeds of rainforest pioneer and secondary shrubs and trees. We suggest three explanations for the different seed-bank structure observed in the seasonally dry forest site. First, with increased deciduousness in rainforests, seed-banks are increasingly subject to invasion and domination by seeds of rapidly maturing herbs. Second, long-lived seeds that germinate in canopy gaps would be less likely to accumulate under deciduous forests because they would he exposed annually to conditions suitable for germination. Third, chronic disturbance by cattle and pigs produces sites suitable for the establishment of rapidly maturing herbs, and possibly disperses their seeds into the forest.     

Viable soil seed banks in disturbed lowland tropical rainforest sites in North Queensland

Four 0.125 m² soil samples, 50 mm deep, from each of eight tropical lowland rainforest sites ranging from primary and secondary forests to degraded Imperata grasslands were exposed to shade-house conditions. Germinations of soil seeds were monitored over 28 weeks in April-October. The viable seed banks in the primary forest (592 m^-2) and the secondary forest sites resulting from one cycle of clearing and abandonment (1300–1400 m^-2) were composed predominantly of secondary species. The viable seed banks were small in Imperata grassland sites that had been burnt regularly (200–400 m^-2) and very large (2000–3000 m^-2) in sites that had not been burnt for five years or more. The seed banks of the burnt and unburnt Imperata grassland sites were composed mostly of agricultural weeds whilst seeds of secondary rainforest trees were rare or absent. Similarities between the species composition of soil seed banks and regrowth vegetation types suggest that soil seed composition is important in determining the initial floristic composition following disturbance and that lack of seed of secondary rainforest trees is one factor which restricts re-growth and secondary succession on degraded Imperata grasslands. Species such as Eucalyptus intermedia R. T. Bak., E. pellita F. Muell. and Imperata cylindrica (L.)Beauv. which can establish and deflect the normal rainforest secondary succession were not present in the soil seed bank, and these species appear to rely on fresh seed inputs, lignotubers or rhizomes to colonize and regenerate after disturbance.     

The rediscovery of Tetrataxis Hooker fil. (Lythraceae)

Tetrataxis, a monotypic endemic of Mauritius, has been known since the 1790s only by the type collection in the Paris Herbarium. Now a colony of seven individuals has been discovered in a valley south-east of the type area. The small trees grow in saturated soil in a low open wet forest. Vegetatively, they resemble the more common Syzygium or Eugenia. Characteristics of the pollen and seed, anatomy of stems and leaves, and an approximate chromosome number are reported for the first time. A lectotype is selected from material of the original collection. Tetrataxis displays a number of advanced characters. It appears to have no close affinity to any single member of the family.     

The Pathoènicity of Two Strains of Tritrichomonas foetus for Mice

SYNOPSIS. The pathogenicity for mice and cell culture, and the growth rates in vitro of two strains of Tritrichomonas foetus were compared. A new strain of T. foetus (T. foetus "G") which was isoated less than a year before use in the experiments described, was more pathogenic to mice but had a longer generation time than an old strain ( T. foetus "M"). The old strain has been maintained in vitro for over five years. The characteristics observed for the strains of T. foetus examined resembled those of T. vaginalis rather than T. gallinae. In strains of the latter species there is a good correlation between growth rate and pathogenicity.     

Root Water Uptake, Leaf Water Storage and Gas Exchange of a Desert Succulent: Implications for Root System Redundancy

A technique used for hydroponics was adapted to measure instantaneousroot water uptake from the soil for a leaf succulent CAM species,Agave deserti. Comparisons were made to previously modelledwater fluxes for A. deserti and to Encelia farinosa, a non-succulentC₃species. Net CO₂uptake and transpiration forA. deserti underwell-watered conditions occurred primarily at night whereasroot water uptake was relatively constant over 24 h. Leaf thicknessdecreased when transpiration commenced and then increased whenrecharge from the stem and soil occurred, consistent with previousmodels. A drought of 90 d eliminated net CO₂uptake and transpirationand reduced the water content of leaves by 62%. Rewetting theentire root system for 7 d led to a full recovery of leaf waterstorage but only 56% of maximal net CO₂uptake. Root water uptakewas maximal immediately after rewetting, which replenished rootwater content, and decreased to a steady rate by 14 d. Whenonly the distal 50% of the root system was rewetted, the timefor net CO₂uptake and leaf water storage to recover increased,but by 30 d gas exchange and leaf water storage were similarto 100% rewetting. Rewetting 10 or 20% of the root system resultedin much less water uptake; these plants did not recover leafwater storage or gas exchange by 30 d after rewetting. A redundancyin the root system of A. deserti apparently exists for dailywater uptake requirements under wet conditions but the entireroot system is required for rapid recovery from drought.Copyright1999 Annals of Botany Company Agave deserti Engelm., desert, drought, gas exchange, rewetting, roots, succulent, water uptake.     

大鼠bcl-x_L cDNA的克隆和高滴度重组bcl-x_L腺相关病毒的制备

以RT PCR法从大鼠脑组织中克隆bcl XL 基因 ,将其定向插入带rep cap基因和neu基因的三功能腺相关病毒 (AAV)载体 ,转染HeLa细胞并以G4 18筛选 ,然后用腺病毒感染筛选后的细胞克隆 ,包装成重组腺相关病毒 .用带rep cap基因的C12细胞筛选和滴定产生重组腺相关病毒的细胞克隆 ,粗制细胞裂解物中病毒滴度最高只有 3× 10 5IU ml.从产病毒量较高的克隆大量制备重组病毒 ,经肝素柱高压液相亲和层析法纯化、浓缩病毒后获得了高达 4× 10 11IU ml的重组病毒 .为研究脑缺血动物模型中BCL XL 的抗脑细胞凋亡作用打下了基础     

INHIBITION OF PHENOTYPE MODULATION,GROWTH, AND MIGRATION OF VASCULAR SMOOTH MUSCLE CELLS BY A GUANOSINE-RICH 30-MER PHOSPHOROTHIOATE OLIGODEOXYNUCLEOTIDE

The testing of a 30-mer dG-rich phosphorothioate oligodeoxynucleotide (LG4PS) for effects on the behaviour of vascular smooth muscle cells (VSMC)in vitroandin vivois described. LG4PS at 0.3μm inhibited significantly the phenotype modulation of freshly isolated rabbit VSMC, and cell outgrowth from pig aortic explants was inhibited ～80% by 5μm LG4PS. The growth of proliferating rabbit and pig VSMC was inhibited ～70% by 0.3μm and 5μm LG4PS, respectively. Though less marked, the antiproliferative effects of LG4PS on human VSMC were comparable to those obtained with heparin. The cytotoxic effects of LG4PS on VSMCin vitrowere low. Despite these promising results, adventitial application of 2–200nmol LG4PS in pluronic gel failed to reduce vascular hyperplasia in balloon-injured rabbit carotid arteries, and the highest dose caused extensive mortality.