Sequencing Studies of Icr-170 Mutagenic Specificity in the am (Nadp-Specific Glutamate Dehydrogenase) Gene of NEUROSPORA CRASSA

The acridine half-mustard ICR-170-induced reversion of the mutant am15, which has a single base-pair deletion, at a frequency of between 9 and 28 X 10(-6). In each of three classes of revertants, the mutagen had induced the insertion of a -G- -C- base pair at a -G-G- -C-C- site. The mutant am6, which has a single base pair insertion, is known to be revertible, with UV light, by deletion of a -G- -C- base pair at a -G-G-G- -C-C-C- site. This mutant reverted with ICR-170 at a frequency of 0.1 X 10(-6). These results show that ICR-170 is able to induce addition frameshifts in Neurospora crassa within short, monotonous runs of G:C base pairs, but indicate a lack of deletion activity at such sequences.     

Chemical limnology of two artificial lakes used for both stormwater management and recreation

The aims of this study were to document the mainly chemical behaviour of two linked artificial lakes used for both stormwater management and recreation in the new town of Craigavon. Further, the understanding of their behaviour should help in their management and the design of other similar lakes.The lake mean total phosphorus (73 µg P l^–1), nitrate (0.50 mg N l^–1) and chlorophyll a (25 µg l^–1) concentrations, Secchi depth (1.2 m) and the estimated total phosphorus loading (1.98 g m^–2 a^–1) all classify the main lake as eutrophic. An important source of the phosphorus load on the lakes is the urban area of Craigavon (52% of the total load). The interrelationships between total phosphorus, chlorophyll a and Secchi depth in the main lake are similar to those in natural ones. In addition, the lake follows the total phosphorus load — trophic state relationships (lake total phosphorus and chlorophyll a concentrations and Secchi depth) found to apply elsewhere. These two points indicate that the artificial lakes in Craigavon behave similarly to natural ones.     

Transglutaminase and the Neuronal Cytoskeleton in Alzheimer''s Disease

Transglutaminase [EC 2.3.2.13, (R)-glutaminyl-peptide:amine gamma-glutamyltransferase], an enzyme that catalyzes the introduction of glutamine-lysine cross-links into proteins, was purified. Neurofilament and microtubule proteins were substrates for this enzyme but the insoluble neurofibrillary tangles (NFT) isolated from Alzheimer's disease brain were not substrates. In vitro cross-linking of neurofilaments and microtubules by the enzyme did not produce paired helical filaments (PHF), which are the major ultrastructural component of NFT. These results make it unlikely that PHF are formed by the straightforward cross-linking of neurofilaments or microtubules.     

Regional Amino Acid Concentration in the Brains of Rats Exposed to High Pressures

Regional amino acid concentrations were measured in rat brain fixed by microwave irradiation at three levels of elevated atmospheric pressure corresponding to different phases of the high-pressure neurological syndrome [20 atmospheres absolute (ATA), no clinical signs; 60 ATA, tremor; 85 ATA, severe tremor and myoclonic jerks]. No changes in amino acid content occurred at 20 or 60 ATA. At 85 ATA glutamine content increased in hippocampus, striatum, cerebellum, and substantia nigra, and gamma-aminobutyric acid content increased in hippocampus. It is suggested that enhanced glutamate release in various subcortical structures contributes to the myoclonic activity observed at 85 ATA.     

Formation of the acrosome and basal body during spermiogenesis in a marine snail,Nerita picea (Mollusca: Archaeogastropoda)

In Nerita picea the proacrosomal granule is formed basally in the early spermatid from one large cisterna of the Golgi body, with which the other Golgi-derived vesicles fuse. After the proacrosomal granule has attached to the plasma membrane and invaginated to form a cup shape, one cisterna of endoplasmic reticulum inserts into the open end and deposits a granular secretion on the inner surface. Subsequently, the proacrosome migrates along the plasma membrane to the apex of the nucleus, but the Golgi body remains basal, as occurs in other archaeogastropods and also many polychaete annelids. However, the final shape and structure of the acrosome is similar to that of mesogastropods. The annulus attaches the distal centriole to the plasma membrane early in spermiogenesis. The production of the flagellum by the distal centriole not only expands the plasma membrane posteriorly but moves the centriolar complex to the nucleus, causing an invagination of the plasma membrane where it is bound by the annulus. During proacrosome migration, the Golgi body secretes a dense tube around the flagellum, and the mitochondria fuse into two spheres at the base of the nucleus. The nuclear plug that closes off the intranuclear canal until this stage rapidly reorganizes itself into two tubes of material inside the canal. The centrioles continue flagellar production, break away from the annulus, and move deep into the intranuclear canal where they fuse together to form the basal body of the sperm. In the maturing spermatid, the two mitochondria fuse into a single sheath that spirals around the flagellum. The annulus does not migrate posteriorly but remains anterior to the midpiece, which is unusual for a filiform sperm. Spermiogenesis in Nerita picea has features in common with both archaeogastropods and mesogastropods but also has some unique features. These observations lend credence to the idea that the Neritidae are a transitional group between Archaeogastropoda and Mesogastropoda.     

Temporal dynamics of estuarine phytoplankton: A case study of San Francisco Bay

Detailed surveys throughout San Francisco Bay over an annual cycle (1980) show that seasonal variations of phytoplankton biomass, community composition, and productivity can differ markedly among estuarine habitat types. For example, in the river-dominated northern reach (Suisun Bay) phytoplankton seasonality is characterized by a prolonged summer bloom of netplanktonic diatoms that results from the accumulation of suspended particulates at the convergence of nontidal currents (i.e. where residence time is long). Here turbidity is persistently high such that phytoplankton growth and productivity are severely limited by light availability, the phytoplankton population turns over slowly, and biological processes appear to be less important mechanisms of temporal change than physical processes associated with freshwater inflow and turbulent mixing. The South Bay, in contrast, is a lagoon-type estuary less directly coupled to the influence of river discharge. Residence time is long (months) in this estuary, turbidity is lower and estimated rates of population growth are high (up to 1–2 doublings d^–1), but the rapid production of phytoplankton biomass is presumably balanced by grazing losses to benthic herbivores. Exceptions occur for brief intervals (days to weeks) during spring when the water column stratifies so that algae retained in the surface layer are uncoupled from benthic grazing, and phytoplankton blooms develop. The degree of stratification varies over the neap-spring tidal cycle, so the South Bay represents an estuary where (1) biological processes (growth, grazing) and a physical process (vertical mixing) interact to cause temporal variability of phytoplankton biomass, and (2) temporal variability is highly dynamic because of the short-term variability of tides. Other mechanisms of temporal variability in estuarine phytoplankton include: zooplankton grazing, exchanges of microalgae between the sediment and water column, and horizontal dispersion which transports phytoplankton from regions of high productivity (shallows) to regions of low productivity (deep channels).Multi-year records of phytoplankton biomass show that large deviations from the typical annual cycles observed in 1980 can occur, and that interannual variability is driven by variability of annual precipitation and river discharge. Here, too, the nature of this variability differs among estuary types. Blooms occur only in the northern reach when river discharge falls within a narrow range, and the summer biomass increase was absent during years of extreme drought (1977) or years of exceptionally high discharge (1982). In South Bay, however, there is a direct relationship between phytoplankton biomass and river discharge. As discharge increases so does the buoyancy input required for density stratification, and wet years are characterized by persistent and intense spring blooms.     

The disease resistance response in pea is associated with increased levels of specific mRNAs

A cDNA library was constructed using poly(A)⁺RNA fromPisum sativum which had been treated for 8 h with the fungusFusarium solani f. sp.phaseoli. Two thousand four hundred recombinant colonies were screened by differential colony hybridization using³²P-labelled cDNAs prepared from RNA extracted from either noninoculated or inoculated pea tissue. cDNA clones were then selected, which showed greater hybridization with cDNA prepared from pea RNA 8 h post-inoculation than with a cDNA probe from 0 h. Seven distinct hybridization classes were chosen for further study. Northern blot analyses of total cellular RNAs inoculated for 16 h with eitherF. solani phaseoli or water demonstrated that each cDNA clone selected represents an mRNA species which increases substantially in abundance during infection. Results of³H-uridine pulse-labelling experiments suggested that enhanced synthesis is at least partially responsible for the accumulation of the fungus-inducible mRNAs which hybridized with the clones.