The Habitat of Zygodon forsteri (Brid) Mitt. in the New Forest,Hants

Abstract

Seven species are reported here for the first time for South Georgia. Two of these were already known from Tierra del Fuego, Acrolophozia fuegiana Schust. and Marsupella sprucei (Limpr.) H. Bern., but Acrolophozia sulcata Hässel, Marsupella austrogeorgica Hässel, and Marsupella minutula Hässel are described as new. The additional two species which are described, Austrolembidium crassum Hässel and Greeneothallus gemmiparus Hässel, also required the creation of two new genera. The total number of liverwort species now known to be present on South Georgia is sixty-six.     

Morphological adaptation to water uptake and transport in the poikilohydric moss Tortula ruralis

Abstract

In this paper different water-holding and transport adaptations to face the uneven and intermittent distribution of water in the ectohydric moss Tortula ruralis are referred to.

The external conduction of water is operated by different and efficient systems (spaces between adjacent shoots, between leaves, leaves and stems, leaves and rhizoids, life form, etc.) which facilitate absorption and transport of solutions.

Also epi-organ capillary systems (bases and revoluted margin of leaves, a groove, a close network of capillary channels determined by the papillae), intra-organ capillary systems (hyalocysts) and certain amount of internal conduction (conducting parenchyma, stereoma) co-operante to absorb and distribute water to the whole gametophyte.

In addition, some adaptations to xerophytism and heliophytism (life form, disposition of phylloids, hair-points) are discussed.     

Efficiency of antioxidant response in Spartina densiflora: An adaptative success in a polluted environment

The effects of different culture conditions, unpolluted and polluted substrates, on an antioxidative system – antioxidant enzymes, such as catalase, ascorbate peroxidase and guaiacol peroxidase, and ascorbic acid – were investigated to establish its relationship with the acclimatization success of Spartina densiflora. Plants of this species growing in the polluted Odiel marshes (Huelva, Spain) showed high levels of catalase, ascorbate and guaiacol peroxidase activities and ascorbate concentration (reduced and oxidized ascorbate). In addition, we found significant oxidation of the ascorbate pool, since only 40% of ascorbate was reduced, and low levels of photosynthetic pigments, suggesting that an oxidative stress was impairing S. densiflora. Transplantation to an unpolluted substrate in the laboratory led to a gradual change in all tested parameters: antioxidative activities and total ascorbate concentration decreased while the percentage of reduced ascorbate and pigment concentrations increased; these data agreed with the hypothesis that oxidative stress conditions in S. densiflora habitat were due to a polluted substrate. After 28 days, the plants were transplanted for a second time to polluted conditions, equivalent to those in their habitats, and a rapid alteration of the antioxidative system was observed. In the first 24 h, catalase and guaiacol peroxidase activities and ascorbate concentration increased greatly and the percentage of reduced ascorbate fell drastically. Regardless of this fact, ascorbate peroxidase activity did not change until the end of the first week, while photosynthetic pigments declined at a constant rate during the whole culture period. Subsequently, we found that the antioxidative system improved its reductive capacity gradually and slowly – over weeks – but this reductive power was rapidly lost within days or even hours. It may be concluded that S. densiflora undergoes oxidative stress in its natural environment and is able to modulate its antioxidative system, based on the degree of pollution, in order to acclimatize successfully to its fluctuating environment.     

Free energy profiles for H+ conduction along hydrogen-bonded chains of water molecules.

The molecular mechanism for proton conduction along hydrogen-bonded chains, or "proton wires," is studied with free energy simulations. The complete transport of a charge along a proton wire requires two complementary processes: 1) translocation of an excess proton (propagation of an ionic defect), and 2) reorientation of the hydrogen-bonded chain (propagation of a bonding defect). The potential of mean force profile for these two steps is computed in model systems comprising a single-file chain of nine dissociable and polarizable water molecules represented by the PM6 model of Stillinger and co-workers. Results of molecular dynamics simulations with umbrella sampling indicate that the unprotonated chain is preferably polarized, and that the inversion of its total dipole moment involves an activation free energy of 8 kcal/mol. In contrast, the rapid translocation of an excess H+ across a chain extending between two spherical solvent droplets is an activationless process. These results suggest that the propagation of a bonding defect constitutes a limiting step for the passage of several protons along single-file chains of water molecules, whereas the ionic translocation may be fast enough to occur within the lifetime of transient hydrogen-bonded water chains in biological membranes.     

Filamentous fungi of the Windmill Islands, continental Antarctica. Effect of water content in moss turves on fungal diversity

This study presents the effect of water content in moss turves from the Windmill Islands, Wilkes Land, continental Antarctica on the composition of associated filamentous fungi. The two most prevalent mosses were sampled: Grimmia antarctici and Bryum pseudotriquetrum. Results were expressed as dry weights. No relationship was found between water content of the mosses or the surrounding soil and fungal diversity. Ten species of fungi were recovered and all species belong to cosmopolitan taxa. Accepted: 21 June 1999     

The epiphytic bryoflora of the Jbel Bouhalla (Rif,Morocco), including a new variety of moss,Orthotrichum speciosum var. brevisetum

Abstract

The epiphytic bryoflora of Jbel Bouhalla, a mountain sited in the Rif range (northern Morocco), is catalogued, resulting in a list of 48 taxa (45 mosses and 3 liverworts). One new variety, Orthotrichum speciosum var. brevisetum, is described, and some new records are reported: Orthotrichum shawii and O. pallens are new to northern Africa, while Habrodon perpusillus and O. speciosum var. speciosum are new to Morocco.     

Spreading of Bacillus thuringiensis var. israelensis over the water surface by a monolayer carrier

The self-spreading properties of monolayers, acting as carriers for Bacillus thuringlensis var. israelensis, were examined in the laboratory. Drops of mixtures of 0.5 to 5% B. thuringlensis in a liquid monolayer were placed at one end of a narrow static water course, 2 m long. In less than 2 min, a single layer of molecules spread over the water surface and deposited enough B. thuringiensis over the whole 2 m to kill test mosquito larvae in 24 h. The monolayer alone did not kill larvae in 24 h because no vegetation was present to deoxygenate the water overnight. Accelerated biodegradation was simulated carrying surface water into an overflow tank for 6 h, the surface monolayer being replenished until the mixture was exhausted. B. thuringiensis was deposited in decreasing quantity along the course with much reaching the overflow tank. The monolayer can carry B. thuringiensis more than 15 m in the field from a point application, dispensing with the need for spray equipment, particularly relevant in developing countries.The author is with the Institute of Horticultural Research, Worthing Road, Littlehampton, West Sussex BN17 6LP, UK.     

Re-evaluation of osmotic effects as a general adaptative strategy for bacteria in sub-freezing conditions

We studied the molecular mechanisms of adaptation of a Siberian psychrophilic bacterial strain. Upon adaptation to 4 degreesC from 24 degreesC, the major changes observed were in the membrane and cell surface chemistry. There was no evidence for the formation of so-called 'compatible metabolites' that are thought to be responsible for the survival at very low to sub-freezing temperatures. The membrane fatty acids were shorter with an increased amount of unsaturation in the 4 degreesC cells compared to the 24 degreesC cells. The absence of a significant amount of phosphorylation in the membrane lipids at 4 degreesC compared to the levels at 24 degreesC was another significant difference. At 4 degreesC, the cell size was reduced in volume by a factor of approximately 14 compared to its size at 24 degreesC. The polar polysaccharide capsular layer was also significantly reduced. There were no significant changes in the protein profiles indicating that antifreeze proteins were not being produced. The results obtained here are consistent with observations and established theories and principles on and about the behavior of water in confined spaces. These indicate that ordering effects, surface charge and polarity are the key determinants of the freezing point and the type of ice structure that will be formed when water is confined to an area of the size of a bacterial cell.