Quantification of mycelial development of arbuscular mycorrhizal fungi using image analysis

Quantitative and reproducible information concerning the development of the extraradical mycelium of arbuscular mycorrhizal fungi (AMF) is lacking due to the difficulties in extracting, identifying and estimating hyphal lengths. In this study, using a rhizobox growth system, the lengths of hyphae of AMF estimated using an image analysis system were not significantly different from data obtained by a trained observer using a modified grid-line intersect method. The assessment of lengths of hyphae on membrane filters or slides was, however, much quicker using image analysis, and allowed the complete sample to be quantified, unlike the grid-line method where a limited number of fields of view are assessed. The image analysis procedure is objective, observer-independent and less laborious than the manual method of assessment. Of the four different methods of sample preparation compared, membrane filter methods were found to be the most appropriate for quantitative sampling from three non-soil substrates. Glomus monosporum (UKC M3) produced twice as much extraradical mycelium and hyphal length per centimetre of colonised root than G. geosporum (BEG 11) on both leek and linseed in a durite sand at final harvest (63 days). Both AMF also produced more hyphal length per centimetre of colonised root on linseed than on leek. The spatial distribution of both AMF, however, was similar in durite sand and no correlation with levels of NaHCO₃-extractable phosphorus was noted. In a third experiment, with G. manihotis (UKC INDO-1) colonising a tropical forage legume, Pueraria phaseoloides, in two other growth substrates, a different pattern of development of the extra-radical mycelium was observed. Because of a higher content of particulate matter, which collected on the membrane filters, the extraction technique had to be modified to give optimal performance of the image analysis system.     

Control of cell pattern in the developing nervous system: polarizing activity of the floor plate and notochord

Individual classes of neural cells differentiate at distinct locations in the developing vertebrate nervous system. We provide evidence that the pattern of cell differentiation along the dorsoventral axis of the chick neural tube is regulated by signals derived from two ventral midline cell groups, the notochord and floor plate. Grafting an additional notochord or floor plate to ectopic positions, or deleting both cell groups, resulted in changes in the fate and position of neural cell types, defined by expression of specific antigens. These results suggest that the differentiation of neural cells is controlled, in part, by their position with respect to the notochord and floor plate.     

The management of populations of vesicular-arbuscular mycorrhizal fungi in acid-infertile soils of a savanna ecosystem

Topsoil stockpiled for 4 years resulted in an accumulation of NH₄-N at depths of 1m or more in mound, as measured by an ammonia gas-sensing electrode. When leached with water these soils were also found to contain high concentrations of dissolved organic C below 1m. Both NH₄-N and DOC were products of microbial mineralisation of soil organic matter that accumulated under anaerobic conditions. When these soils were restored a flush of decomposition took place, fuelled by labile organic matter and soluble nitrogen.Stockpiled soil which underwent an ammonium-rich perfusion regime in the laboratory indicated that in-mound soils rapidly attained greater nitrification potential than surface mound soils and also had greater potential for further mineralisation of organic matter to NH₄-N. This further production was seen as a contribution from the bacterial flush, stimulated by the large labile-C pool already present.As the bulk of stored soil was anaerobic, restored soils were seen as potentially wasteful of their N-reserves; the fate of nitrogen and soluble carbon compounds in restored soils is discussed.     

Hierarchical genetic structure in fragmented populations of the Little Pocket Mouse (Perognathus longimembris) in Southern California

The geographic genetic structure, based onsequence variation of an 810 base pair fragmentof the mitochondrial cytochrome b gene,is described for populations of five subspeciesof the Little Pocket Mouse, Perognathuslongimembris, from Southern California. Oneof these, P. l. pacificus (Pacific PocketMouse), is listed as Endangered by the U.S.Federal Government. Sixty-two uniquehaplotypes were recovered from 99 individualssampled. Phylogenetic analyses of thesevariants do not identify regionallyreciprocally monophyletic lineages concordantwith the current subspecies designations, butmost haplotypes group by subspecies in networksgenerated by either statistical parsimony ormolecular variance parsimony. Moreover, asubstantial proportion of the total pool ofhaplotype variation is attributed to thesesubspecies, or to local populations withingeographic segments of each, indicating theirrelative evolutionary independence. The pooledextant populations of the endangered PacificPocket Mouse exhibit the same levels ofnucleotide and haplotype diversity as other,presumptively less-impacted populations ofadjacent subspecies, although the sample fromDana Point, Orange County, has markedly lowhaplotype diversity in comparison to allothers. These populations also show a geneticsignature of population expansion rather thanone of decline. Both pieces of evidence are atodds with current empirical populationestimates, which reinforces the fact thatpresent-day patterns of genetic diversity arethe product of coalescent history and will notnecessarily reflect recent anthropogenic, orother, perturbations. Comparison of haplotypevariation within and among extant populationsof the Pacific Pocket Mouse with those obtainedfrom museum samples collected more than 70years ago suggests that the pattern ofpopulation differentiation and diversity was inplace before the post-World War II exponentialurbanization of Southern California.     

The synthesis and biological evaluation of non-peptidic matrix metalloproteinase inhibitors.

Novel sulfonamide matrix metalloproteinase inhibitors of general formula (9) were synthesised by a route involving a stereoselective conjugate addition reaction. Enzyme selectivity was found to be dependant on the nature of the sulfonamide substituents. Compounds (9f, 9q) are potent selective collagenase inhibitors with good oral bioavailability.