The influence of soil moisture and flooding on formation of VA-endo- and ectomycorrhizae in Populus and Salix

Native mixtures of extomycorrhizal fungi were found to infect Populus and Salix roots primarily in very moist but well drained soils in both the field and in controlled experiments (0 to –0.2 MPa), whereas native mixtures of VA-endomycorrhizal fungi infected roots over a much wider range of soil moisture (flooded to –3.4 MPa). Although a moisture gradient experiment showed endomycorrhizal formation was greater in moist soil than in very dry or flooded soils, this pattern was reversed in field transects along drainage gradients. Infection by VA-endomycorrhizal fungi in the field was the lowest where infection by ectomycorrhizal fungi was high, which suggests possible antagonism among the fungal symbionts. The narrow moisture range for ectomycorrhizal formation, and antagonism among endo- and ectomycorrhizal fungi, apparently combine to produce the mycorrhizal distributions found in nature.     

DECREASE IN NUCLEAR FEULGEN-POSITIVE MATERIAL (DNA) UPON AGING IN IN VITRO STORAGE OF BOVINE SPERMATOZOA

The Feulgen-DNA content of sperm cells from 5 bulls was studied by means of microspectrophotometry after storage at 5°C for 2, 3, 5, and 10 days in a yolk-citrate diluent permitting slow aerobic metabolism. A subsample of sperm cells from each bull was subjected to the Feulgen technique on each of the storage days selected. The cells sampled on each of these days received a standard 12 minute, 60°C hydrolysis. Absorption measurements at 546 mµof the individual cells indicated a marked progressive decrease in the Feulgen-DNA content of the stored spermatozoa. The loss of 30 per cent of the initial DNA at the end of 5 days' storage was highly significant statistically. This decrease approximately parallels the known decrease in fertility of stored sperm cells, as well as the increase in apparent embryonic mortality resulting from the use of similarly aged spermatozoa for artificial insemination.     

Functional diversity in vascular endothelial cells: role in coxsackievirus tropism.

Six plaque-purified virus isolates were obtained from liver and heart tissues of a DBA/2 mouse infected 7 days earlier with 10(4) PFU of coxsackievirus group B type 3. Each virus isolate was assayed in vitro for infectivity to vascular endothelial cells (VEC) of the liver, lungs, and heart. Both the percentage of VEC infected and the mean progeny PFU produced per infected VEC were determined. Virus isolates from the heart showed greater infectivity and replication in heart VEC than in VEC derived from either the liver or lungs. Similarly, virus isolated from the liver preferentially infected liver VEC. Virus receptor expression varied between VEC populations, as demonstrated by binding studies with a [35S]methionine-radiolabeled heart virus and by enzyme-linked immunoadsorption assay studies with a monoclonal antibody to the coxsackievirus group B type 3 receptor on heart tissue. Finally, the heart and liver virus isolates were injected (10(4) PFU) intraperitoneally into BALB/c mice. After 7 days, the animals were sacrificed, and the hearts, livers, and lungs were evaluated for tissue injury and virus concentrations. Viruses originally isolated from the heart preferentially infected the heart when reinjected into animals and caused severe myocarditis. Viruses originally derived from the liver most consistently reinfected the liver, although significant virus concentrations were also detected in the heart. The liver virus isolates, however, were incapable of causing myocarditis. Thus, selective tropism of viruses for particular organs in vivo corresponds to the ability of these isolates to infect VEC in vitro.     

Cloning, sequencing and analysis of the structural gene and regulatory region of the Pseudomonas aeruginosa chromosomal ampC beta-lactamase.

The chromosomal gene from Pseudomonas aeruginosa encoding beta-lactamase has been cloned, and the sequence determined and compared with corresponding sequences of beta-lactamases from members of the enterobacteriaceae. Upstream of the beta-lactamase gene is an open reading frame which we postulate encodes a regulatory protein, AmpR. We identified a helix-turn-helix region in AmpR and a putative AmpR-binding site.     

Factors related to diversity of decomposer fungi in tropical forests

Recent studies suggest that host-preferences are common among certain groups of tropical fungal decomposers but rare in others, and sometimes occur where we least expect them. Host preferences among microfungi and ascomycetes that decompose leaf litter are common but usually involve differences in relative frequencies more than presence/absence, so their diversity may be loosely correlated with species richness of host trees. Strong host-specificity appears to be rare among wood decomposer fungi, whereas characteristics of their substrata and habitat are very important for this group. Anthropogenic disturbance predisposed a tropical forest to subsequent hurricane damage, and the resulting direct and indirect effects on host diversity and habitat heterogeneity were reflected in the decomposer fungal community more than sixty years after the original disturbance. While species richness of dictyostelid slime molds and functional diversity of their bacterial prey increased with disturbance, the more diverse microfungi and ascomycetes were apparently negatively affected by disturbance.     

Mitochondrial DNA sequence evolution in sharks: rates, patterns, and phylogenetic inferences

Abundant representation of sharks in the fossil record makes this group a superb system in which to investigate rates and patterns of molecular evolution and to explore the strengths and weaknesses of phylogenetic inferences from molecular data. In this report, the molecular evolution of the cytochrome b gene in sharks is described and the information related to results from phylogenetic analysis of the data evaluated in the light of a phylogeny derived independently of the molecular data. Across divergent lineages of sharks there is evidence for significant substitution rate variation, departure from compositional equilibrium, and substantial homoplasy; nevertheless, the signal of evolutionary history is evident in patterns of shared transversions and amino acid replacements.      

Metabolic rate and directional nucleotide substitution in animal mitochondrial DNA

There is marked heterogeneity of nucleotide composition in mitochondrial DNA across divergent animals. Differences in nucleotide composition presumably reflect differences in directional nucleotide substitution for A+T or G+C nucleotides. In mitochondrial DNA, there is A+T directional nucleotide substitution in most (if not all) animals surveyed, and the magnitude of directional A+T nucleotide substitution differs greatly within and among groups. Differences in directional nucleotide substitution among lineages of mammals can be explained by changes in metabolic physiology. This relationship is thought to be mediated by the effect of oxygen radicals because these toxic compounds are by-products of aerobic metabolism and are known mutagens. Association between metabolism and nucleotide composition provides additional evidence in favor of the hypothesis that rates and patterns of nucleotide substitution in mitochondrial DNA can be influenced by factors that impinge on rates of endogenous DNA damage.      

Elemental distribution in striated muscle and the effects of hypertonicity: Electron probe analysis of cryo sections

A method of rapid freezing in supercooled Freon 22 (monochlorodifluoromethane) followed by cryoultramicrotomy is described and shown to yield ultrathin sections in which both the cellular ultrastructure and the distribution of diffusible ions across the cell membrane are preserved and intracellular compartmentalization of diffusabler ions can be quantitated. Quantitative electron probe analysis (Shuman, H., A.V. Somlyo, and A.P. Somlyo. 1976. Ultramicros. 1:317-339.) of freeze-dried ultrathin cryto sections was found to provide a valid measure of the composition of cells and cellular organelles and was used to determine the ionic composition of the in situ terminal cisternae of the sarcoplasmic reticulum (SR), the distribution of CI in skeletal muscle, and the effects of hypertonic solutions on the subcellular composition if striated muscle. There was no evidence of sequestered CI in the terminal cisternae of resting muscles, although calcium (66mmol/kg dry wt +/- 4.6 SE) was detected. The values of [C1](i) determined with small (50-100 nm) diameter probes over cytoplasm excluding organelles over nuclei or terminal cisternae were not significantly different. Mitochondria partially excluded C1, with a cytoplasmic/ mitochondrial Ci ratio of 2.4 +/- 0.88 SD. The elemental concentrations (mmol/kg dry wt +/- SD) of muscle fibers measured with 0.5-9-μm diameter electron probes in normal frog striated muscle were: P, 302 +/- 4.3; S, 189 +/- 2.9;C1, 24 +/- 1.1;K, 404 +/- 4.3, and Mg, 39 +/- 2.1. It is concluded that: (a) in normal muscle the "excess CI" measured with previous bulk chemical analyses and flux studies is not compartmentalized in the SR or in other cellular organelles, and (b) the cytoplasmic C1 in low [K](0) solutions exceeds that predicted by a passive electrochemical distribution. Hypertonic 2.2 X NaCl, 2.5 X sucrose, or 2.2 X Na isethionate produced: (a) swollen vacuoles, frequently paired, adjacent to the Z lines and containing significantly higher than cytoplasmic concentrations of Na and Cl or S (isethionate), but no detectable Ca, and (b) granules of Ca, Mg, and P = approximately (6 Ca + 1 Mg)/6P in the longitudinal SR. It is concluded that hypertonicity produces compartmentalized domains of extracellular solutes within the muscle fibers and translocates Ca into the longitudinal tubules.