The ecology of ectomycorrhiza formation and functioning

Factors in inoculum potential/infection levels/plant growth response are analysed and experimental approaches to propagule germination, growth through soil and rhizosphere growth are indicated. It is suggested that seedling rhizosphere germination of basidiospores occurs particularly with early stage fungi, while late stage fungi may be advantaged by germination/growth on exudates from older parts of roots or on litter (and its associated microorganisms) and their tolerance of antimicrobial substances in litter. Relative growth in the rhizosphere is likely to dominate the mycorrhizal species composition and this may be a good selection method for organisms tolerant of stress and pollution conditions. As mycorrhizal function in nutrient uptake is largely determined by fungus growth into soil, there is need for much more experimental study of factors affecting this, and of the potential photosynthate drain this could represent. The possibility of selection/breeding mycorrhizal fungi with both ‘early stage’ and ‘late stage’ attributes is raised.     

Serotonergic pathology is not widespread in Alzheimer patients without prominent aggressive symptoms

Behavioural symptoms of Alzheimer's disease, such as aggression, may determine the care patients required. Most postmortem neurochemical studies have been of institutionalized patients and conclusions drawn from these may not be valid for all patients. We have shown that serotonin 2 receptors are not lost from 12 of the 13 areas of cerebral cortex examined in the patients assessed to be free of aggressive symptoms. This has been interpreted as representing the relative preservation of cortical interneurones. In contrast choline acetyltransferase activity was reduced in all areas whereas serotonin content was reduced in only 2 of the 4 areas examined.Abbreviations AD Alzheimer's disease - ChAT choline acetyltransferase activity - GABA gamma-amino butyric acid - 5-HT serotonin - SLIR somatostatin-like immuno-reactivity Special issue dedicated to Dr. Alan N. Davison.     

Mitochondrial DNA evolution at a turtle's pace: evidence for low genetic variability and reduced microevolutionary rate in the Testudines.

Evidence is compiled suggesting a slowdown in mean microevolutionary rate for turtle mitochondrial DNA (mtDNA). Within each of six species or species complexes of Testudines, representing six genera and three taxonomic families, sequence divergence estimates derived from restriction assays are consistently lower than expectations based on either (a) the dates of particular geographic barriers with which significant mtDNA genetic clades appear associated or (b) the magnitudes of sequence divergence between mtDNA clades in nonturtle species that otherwise exhibit striking phylogeographic concordance with the genetic partitions in turtles. Magnitudes of the inferred rate slowdowns average eightfold relative to the "conventional" mtDNA clock calibration of 2%/Myr sequence divergence between higher animal lineages. Reasons for the postulated deceleration remain unknown, but two intriguing correlates are (a) the exceptionally long generation length most turtles and (b) turtles' low metabolic rate. Both factors have been suspected of influencing evolutionary rates in the DNA sequences of some other vertebrate groups. Uncertainities about the dates of cladogenetic events in these Testudines leave room for alternatives to the slowdown interpretation, but consistency in the direction of the inferred pattern, across several turtle species and evolutionary settings, suggests the need for caution in acceptance of a universal mtDNA-clock calibration for higher animals.     

The fine structural localization of acid phosphatase activity inPolycelis tenuis (Iijima)

Protoplasma - A variety of substrates and incubating conditions have been used to localize acid phosphatase at the fine structural level in the normal, adult planarian wormPolycelis tenuis. Enzyme...     

Molecular dynamics simulation of crack growth in pure titanium under uniaxial tension

The analysis of crack growth in titanium was performed using molecular dynamics simulation with Embedded Atom Method potentials. The effect of temperature and strain rate on the mechanism of crack growth and the change of microstructure were discussed. After setting an initial crack, the specimen was subjected to uniaxial tension strain up to the total strain level of 0.2 with a constant strain rate. During the period, the shape and the microstructure of crack tip as well as the stress–strain curves were monitored. In the simulation, the gather of voids and stress concentration leading to the crack growth occurred, which are in agreement with experimental results observed by transmission electron microscopy. The transformation from HCP to BCC also occurred at crack tip. The remarkable effect of temperature and strain rate on the growth direction and rate of stacking fault of crack tip was observed. Moreover, initial crack greatly lowered the tension yield point of pure titanium. In the stage of deformation, simulation results showed that loading strain rate and temperature strongly influenced peak stress point, which was increased by the low temperature and high strain, whereas the initial slope of the stress strain curve was independent of loading strain rate.     

Groundcover management changes grapevine root fungal communities and plant-soil feedback

Plant and Soil - The objective of this study was to determine if vineyard groundcover management can mitigate negative plant-soil feedback caused by soil borne pathogens through changes in root...     

Behavioral and trophic plasticity of juvenileTilapia mossambica in utilization of the unstable littoral habitat

Synopsis JuvenileTilapia mossambica Peters (2.5–10.0 cm standard length) in Lake Sibaya, South Africa, move daily from deep offshore waters to shallow (<0.5 m) littoral areas where they feed for several hours and then return to deep water. The timing of these movements varies in response to changing physical and biological features of the littoral environment. During this study (December 1973 – February 1976), lake level rose more than 1 m. At the start of the study, littoral areas visited by juvenileT. mossambica were free of vegetation and debris, but at higher lake levels trees and brush from the eroding shoreline were common in nearshore littoral waters. When the littoral zone was free of debris, juvenileT. mossambica visited nearshore waters only during daylight hours. After a 0.65 m rise in lake level and considerable accumulation of debris, these fish were abundant in the littoral zone only at night. This reversal can be attributed to efforts by juvenileT. mossambica to avoid their principal predator, the catfishClarias gariepinus. At low lake levelC. gariepinus ventured into the littoral only at night but at higher lake levels this predator was found within flooded vegetation during the day. When further increases in lake level flooded marginal grasslands, juvenileT. mossambica abandoned the littoral zone in favor of this newly created eulittoral habitat where potential fish predators did not occur. With the change in habitat, the diet changed from benthic detrital aggregate to periphyton. These observations suggest the importance of behavioral and throphic plasticity in the ability of tilapia to utilize unstable habitats.