Parasitic castration of plants by fungi

If the production of genetically variable offspring is a mechanism of host defense against parasites, then parasites capable of suppressing sexual reproduction in hosts may gain a selective advantage over parasites that do not do so. Recent work has shown that a range of systemic fungi infecting plants sterilize their hosts, effectively preventing coevolutionary responses by host populations to avoid infection, while stimulating clonal spread of the infected plant. Indeed, parasitic castration of plants may represent a widespread fungal adaptation.     

CO_H(N)CACB experiments for assigningbackbone resonances in 13C/15N-labeledproteins

A triple resonance NMR experiment, denoted CO_H(N)CACB, correlates¹H^N and ¹³CO spins with the¹³C and¹³C spins of adjacent amino acids. Thepulse sequence is an out-and-back design that starts with¹H^N magnetization and transfers coherence viathe ¹⁵N spin simultaneously to the ¹³CO and¹³C spins, followed by transfer to the¹³C spin. Two versions of the sequence arepresented: one in which the ¹³CO spins are frequency labeledduring an incremented t₁ evolution period prior to transfer ofmagnetization from the ¹³C to the¹³C resonances, and one in which the¹³CO spins are frequency labeled in a constant-time mannerduring the coherence transfer to and from the¹³C resonances. Because ¹³COand ¹⁵N chemical shifts are largely uncorrelated, thetechnique will be especially useful when degeneracy in the¹H^N-¹⁵N chemical shifts hindersresonance assignment. The CO_H(N)CACB experiment is demonstrated usinguniformly ¹³C/¹⁵N-labeled ubiquitin.     

On the role of subthreshold dynamics in neuronal signaling

The role of subthreshold dynamics in neuronal signaling is examined using periodic pulse train stimulation of the Fitzhugh-Nagumo (FN) model of nerve membrane excitability and results from the squid giant axon as an experimental data base. For a broad range of stimulus conditions the first pulse in a pulse train elicited an action potential, whereas all subsequent pulses elicited subthreshold responses, both in the axon and in the FN model. These results are not well described by the Hodgkin and Huxley 1952 model. Various different patterns of subthreshold responses, including chaotic dynamics, can be observed in both systems-the FN model and the axon-depending upon stimulus conditions. For some conditions action potentials are occasionally interspersed among the subthreshold events with randomly occurring interspike intervals. The randomness is directly attributable to the underlying subthreshold chaos-deterministic chaos-rather than to a stochastic noise source. We conclude that this mechanism may contribute to multimodal interspike interval histograms which have been observed from individual neurons throughout the nervous system.     

Evidence for the involvement of the NADPH oxidase enzyme complex in the optimal accumulation of Platelet-activating factor in the human cell line PLB-985.

Platelet-activating factor (PAF) is an early product of the inflammatory environment, influencing development and resolution of inflammation. Its production is greater in neutrophils and macrophages, which predominantly synthesize 1-alkyl sn-2 acetyl glycerophosphocholine (GPC) than in nongranulocytes (B cells and endothelial cells), which lack a respiratory burst and synthesize 1-acyl sn-2 acetyl GPC as their major PAF species. This study investigated whether the respiratory burst was responsible for the quantitative and qualitative differences in sn-2 acetyl GPC species generation by neutrophils and macrophages versus those cells lacking the NADPH oxidase complex. The myeloid cell line PLB-985 (capable of differentiation into neutrophils) was used to test this hypothesis, since these cells had previously been generated with a non-functional respiratory burst (X-CGD PLB-985). Differentiated PLB-985 cells underwent a large respiratory burst in response to PMA (phorbol ester), and smaller respiratory bursts in response to A23187 (calcium ionophore), and the bacterial polypeptide fMLP (receptor mediated activation). Concurrently, treated cells were assessed for production of 1-hexadecyl and 1-palmitoyl sn-2 acetyl GPC species by gas chromatography/mass spectrometry. Neither cell type generated these lipid species in response to PMA, but both cell types generated equal levels of sn-2 acetyl GPC in response to A23187, with five times more 1-hexadecyl than 1-palmitoyl species. Upon fMLP activation, X-CGD PLB-985 cells produced significantly less 1-hexadecyl and 1-palmitoyl sn-2 acetyl GPC in comparison to the wild-type PLB-985 cells. These findings suggest phagocytic oxidant production by NADPH oxidase is not essential for sn-2 acetyl GPC generation, but appears important for optimal production of PAF in response to some stimuli.     

Dynamics of a Lactate Dehydrogenase Polymorphism in the Wood Louse PORCELLIO SCABER Latr.: Evidence for Partial Assortative Mating and Heterosis in Natural Populations

Electrophoretic separation of lactate dehydrogenase (LDH) of Porcellio scaber from 14 natural populations in California, and one each in Oregon, Delaware and Massachusetts, indicates a biallelic polymorphism. Phenotypes are recovered from laboratory matings of virgin females in frequencies agreeing with simple Mendelian inheritance, and the frequency distributions of phenotypes in natural populations are typically in agreement with the appropriate Hardy-Weinberg distributions for these same populations. The same allele predominates in all natural populations examined. Temporal stability within populations suggests that the polymorphism is at, or near, equilibrium. The spatial distribution of allele frequencies, however, is apparently mosaic. Abrupt discontinuities in gene frequency over short distances (50 m to 1 km) suggest that interpopulation migration is insufficient to swamp local differences in gene frequency. Analysis of the transmission dynamics of the polymorphism in natural populations using mother-offspring genotype comparisons suggests that the allelic frequencies of transmitted male gametes are not independent of female genotype. Specifically, the observed mating scheme in natural populations appears to be partially assortative. Comparisons of progeny genotype distributions with yearling (or adult) genotype distributions from the same populations indicate a superior post-partum viability of heterozygous individuals relative to homozygotes. The distortion of progeny genotypic distributions created by assortment is thus apparently counteracted by subsequent heterosis.     

Particle size,percent organic carbon,phosphorus, mineralogy,and deposition of sediments in Ham's and Arbuckle lakes

Several sediment parameters were examined in a 40 ha lake with a maximum depth of 9 m and in a 950 ha lake, 26 m deep, from May through October, 1977. Particle size was finer at the deeper stations than at the shallower stations in both lakes. Sediments of the shallow stations generally had a more even grain size distribution. Variation in percent organic carbon and phosphorus among stations of different depths was not significant. However, temporal variation of phosphorus was significant as values increased during summer. Kaolinite was the dominant clay particle in both lakes, but the sediments also included quartz, mica, montmorillonite, and a montmorillonite-vermiculite interlayer. Sedimentation rate was inversely related to depth in the larger lake, while variation among stations in the smaller lake was slight.Research supported with funds from the Office of Water Research and Technology and the Bureau of Reclamation     

Symbiosis and the Regulation of Communities

Ecologists have long been interested in factors that controlthe structure of communities and the relative importance oftop-down effects of predators versus bottom-up effects of resources.There is a growing body of evidence that microbial symbiosesare important determinants of plant community structure andindirectly affect herbivore and predator trophic levels. Studieswith mycorrhizal fungi, N-fixing bacteria and endophytes ofgrasses have demonstrated that they can affect competition,coexistence, soil nutrient dynamics and plant-herbivore interactions.Long-term field experiments with one grass/endophyte interactionsuggest that grassland community structure is determined bythe fungus. While total plant productivity of experimental plotswas similar, the composition of the vegetation was altered byendophyte symbiosis. The host grass tall fescue (Festuca arundinacea)dominated plots when infected while other grasses greatly increasedin uninfected plots. Indirect evidence suggests that changesin prairie vole (Microtus ochrogaster) grazing patterns andreproductive physiology may be in part responsible for vegetationalchanges. These results provide evidence that, in addition tobottom-up and top-down forces, microbial symbionts of plantsare important determinants of community structure.     

Weight Loss Attempts and Attitudes toward Body Size,Eating, and Physical Activity in American Indian Children: Relationship to Weight Status and Gender

Objective: This study examined dieting, weight perceptions, and self‐efficacy to eat healthy foods and engage in physical activity and their relationships to weight status and gender among American Indian elementary schoolchildren. Research Methods and Procedures: Data for this study were collected as part of the baseline examination for the Pathways study. Participants were 1441 second‐ through third‐grade American Indian children in 41 schools representing seven tribes in Arizona, New Mexico, and South Dakota who filled out a questionnaire and had heights and weights taken. Results: Forty‐two percent of the children were overweight or obese. No differences were found between overweight/obese and normal weight children for healthy food intentions or self‐efficacy. Heavier children (especially those with body mass index > 95th percentile) were more likely to have tried to lose weight or were currently trying to lose weight. No gender differences were found. Normal weight children chose a slightly heavier body size as most healthy compared with overweight/obese children. Discussion: The results indicate that children are concerned about their weight and that weight modification efforts are common among overweight American Indian children. School, community, and family‐based programs are needed to help young people adopt lifelong healthful eating and physical activity practices.     

Variation in horizontal and vertical transmission of the endophyte Epichloë elymi infecting the grass Elymus hystrix

Systemic fungal endophytes (Clavicipitaceae) of grasses reproduce sexually when the fungus forms stromata and contagious ascospores, or asexually by vertical transmission of hyphae into seeds and seedlings. Vertical transmission is predicted to favor reduced virulence compared with horizontal transmission in systems with both types of transmission. Here, variation in vertical and horizontal transmission and its potential heritability in a host grass-endophyte interaction, Elymus hystrix infected with Epichlo? elymi, were examined in natural populations and two common garden experiments using field-collected host tillers and seed progeny of maternal plants with known infection phenotypes. Transmission mode exhibited year-to-year variation in field and common garden environments. In the common garden there were consistent differences among maternal plant families in stroma production and significant correlations between stroma production in the common garden and in natural populations. Transmission mode differed among maternal families, spanning a continuum from pure vertical transmission to a high proportion of stroma production and horizontal transmission potential. Vertical transmission to seeds occurred at high rates in all maternal families regardless of their stroma production. Observed patterns of variation indicate that endophyte transmission mode and correlated changes in virulence can respond to selection by biotic and abiotic factors.