Variation in growth rate,carbon assimilation,and photosynthetic efficiency in response to nitrogen source and concentration in phytoplankton isolated from upper San Francisco Bay

Six species of phytoplankton recently isolated from upper San Francisco Bay were tested for their sensitivity to growth inhibition by ammonium (NH₄⁺), and for differences in growth rates according to inorganic nitrogen (N) growth source. The quantum yield of photosystem II (F_v/F_m) was a sensitive indicator of NH₄⁺ toxicity, manifested by a suppression of F_v/F_m in a dose‐dependent manner. Two chlorophytes were the least sensitive to NH₄⁺ inhibition, at concentrations of >3,000 μmoles NH₄⁺ · L^?1, followed by two estuarine diatoms that were sensitive at concentrations >1,000 μmoles NH₄⁺ · L^?1, followed lastly by two freshwater diatoms that were sensitive at concentrations between 200 and 500 μmoles NH₄⁺ · L^?1. At non‐inhibiting concentrations of NH₄⁺, the freshwater diatom species grew fastest, followed by the estuarine diatoms, while the chlorophytes grew slowest. Variations in growth rates with N source did not follow taxonomic divisions. Of the two chlorophytes, one grew significantly faster on nitrate (NO₃^?), whereas the other grew significantly faster on NH₄⁺. All four diatoms tested grew faster on NH₄⁺ compared with NO₃^?. We showed that in cases where growth rates were faster on NH₄⁺ than they were on NO₃^?, the difference was not larger for chlorophytes compared with diatoms. This holds true for comparisons across a number of culture investigations suggesting that diatoms as a group will not be at a competitive disadvantage under natural conditions when NH₄⁺ dominates the total N pool and they will also not have a growth advantage when NO₃^? is dominant, as long as N concentrations are sufficient.     

Relationship of Physical Fitness to Prevalence and Incidence of Overweight among Schoolchildren

Objectives: We examined the relationship between comprehensive fitness tests and overweight using a school surveillance system in a racially diverse city in the United States. Research Methods and Procedures: Trained physical education teachers measured weight, height, and fitness annually from 2001 to 2003. We compiled data for a cross‐sectional analysis (11, 845 measurements on 6297 students, 5 to14 years of age) and a 1‐year prospective analysis (4215 measurements on 2927 students not overweight at baseline, 5 to 13 years of age). Overweight was defined as a BMI ≥95th percentile (Centers for Disease Control and Prevention 2000 growth charts), and underfit was defined as failing at least one of five fitness tests: endurance run, abdominal strength, flexibility, upper body strength, and agility (Amateur Athletic Union and Fitnessgram). Associations between fitness and overweight were examined using multivariate logistic regression models, adjusting for sociodemographic status and repeated measurements over time. Results: The mean number of fitness tests passed was lower among students with a BMI above the 80th percentile. Overweight incidence over 1 year was 7% and 2% for underfit and fit girls, respectively (odds ratio, 3.3; 95% confidence interval, 2.0 to 5.6). Not passing either the endurance run or upper body strength test was associated with overweight incidence in both boys and girls. After adjusting for baseline BMI, the endurance run remained a significant predictor of incident overweight among girls (odds ratio, 2.0; 95% confidence interval, 1.1 to 3.5). Discussion: Findings support a cross‐sectional inverse relationship between physical fitness and overweight among school‐aged children. The direction of causation between fitness and overweight is not clearly established and merits further study.     

Anatomy and ultrastructure of epidermal cells in the haustorium of a parasitic flowering plant,Cuscuta japonica, during attachment to the host

Changes of epidermal cells in the haustorium of the parasiticCuscuta japonica during its attachment to the host plantimpatiens balsamina were studied with light and electron microscopy. In the transverse sections of dodder stems not in contact with the host, epidermal cells had rounded outlines. However, when haustorial initials developed in the cortex of the parasite stem at the contact site, the epidermal cells had more dense cytoplasm and conspicuous nuclei than before, and their outline was flat in the longitudinal section. As meristem cells developed from those initials, the epidermal cells became more elongated. When the haustorium was fully matured, the apical tips of the elongated epidermal cells at the contact site branched like toes, producing numerous projections via cell wall invaginations. This event caused spaces to form between the projections; coincidently, the surface area of the apical ends of the epidermal cells increased. The dense cytoplasm at those projections contained prominent nuclei and abundant other organelles, suggesting a active metabolism. Osmiophilic particles, releasing into the cell walls from the cytoplasm, were though to be associated with the loosening and elongating of the epidermal cell walls. Dense and homogeneous materials were secreted within the spaces between the projections. These materials could play an important role in cementing the haustorium onto the surface of the host organ.     

Medicinal properties of Echinacea: A critical review

Preparations from Echinacea purpurea are among the most widely used herbal medicines. Most uses of E. purpurea are based on the reported immunological properties. A series of experiments have demonstrated that E. purpurea extracts do indeed demonstrate significant immunomodulatory activities. Among the many pharmacological properties reported, macrophage activation has been demonstrated most convincingly. Phagocytotic indices and macrophage-derived cytokine concentrations have been shown to be Echinacea-responsive in a variety of assays. Activation of polymorphonuclear leukocytes and natural killer cells has also been reasonably demonstrated. Changes in the numbers and activities of T- and B-cell leukocytes have been reported, but are less certain. Despite this cellular evidence of immunostimulation, pathways leading to enhanced resistance to infectious disease have not been described adequately. Several dozen human experiments--including a number of blind randomized trials--have reported health benefits. The most robust data come from trials testing E. purpurea extracts in the treatment for acute upper respiratory infection. Although suggestive of modest benefit, these trials are limited both in size and in methodological quality. Hence, while there is a great deal of moderately good-quality scientific data regarding E. purpurea, effectiveness in treating illness or in enhancing human health has not yet been proven beyond a reasonable doubt.     

Composition and structure of phytoplankton in lowland rivers of the upper Ob basin

Taxonomic composition and structure of the phytoplankton were studied in the lowland rivers of the upper Ob basin: Barnaulka, Bol’shaya Losikha, and lower Inya. It has been shown that the phytoplankton of a large river system in Eurasia, exemplified by the Ob basin, is characterized by spatial heterogeneity in its taxonomic composition.     

Evaluating future success of whitebark pine ecosystem restoration under climate change using simulation modeling

Major declines of whitebark pine forests throughout western North America from the combined effects of mountain pine beetle (Dendroctonus ponderosae) outbreaks, fire exclusion policies, and the exotic disease white pine blister rust (WPBR) have spurred many restoration actions. However, projected future warming and drying may further exacerbate the species' decline and possibly compromise long‐term success of today's restoration activities. We evaluated successes of restoration treatments under future climate using a comprehensive landscape simulation experiment. The spatially explicit, ecological process model FireBGCv2 was used to simulate whitebark pine populations on two U.S. Northern Rocky Mountain landscapes over 95 years under two climate, three restoration, and two fire management scenarios. Major findings were that (1) whitebark pine can remain on some high mountain landscapes in a future climate albeit at lower basal areas (50% decrease), (2) restoration efforts, such as thinning and prescribed burning, are vital to ensure future whitebark pine forests, and (3) climate change impacts on whitebark pine vary by local setting. Whitebark pine restoration efforts will mostly be successful in the future but only if future populations are somewhat resistant to WPBR. Results were used to develop general guidelines that address climate change impacts for planning, designing, implementing, and evaluating fine‐scale restoration activities.     

Plant Functional Traits and the Distribution of West African Rain Forest Trees along the Rainfall Gradient

Plant morphological and physiological traits affect the way plants tolerate environmental stresses and therefore play an important role in shaping species distribution patterns in relation to environmental gradients. Despite our growing knowledge on the role of functional traits in structuring plant communities, few studies have tested their importance at large scales in the wet tropics. Here, we describe the distribution patterns of the most important West African rain forest timber species along the regional rainfall gradient and relate them to their functional traits. We found that the distribution patterns of 25 out of the 31 studied species (80%) were significantly related to mean annual rainfall. Shade tolerance and drought resistance were identified as the main strategy axes of variation. Wood density and leaf deciduousness emerged as the best predictor traits of species position along the rainfall gradient, explaining respectively 32 and 15 percent of the variation. Species traits tended to show stronger relationships with estimated optimum annual rainfall for each species than to the extreme rainfall conditions where they occur. The significant role of rainfall in shaping timber species distribution and the strong relationships between species traits and rainfall indicate that changes in climate, especially declining rainfall, could have strong effects on species composition and abundance in these tropical forests.     

Intrinsic motions in the N-terminal domain of an ionotropic glutamate receptor detected by fluorescence correlation spectroscopy

Ionotropic glutamate receptors (iGluRs) mediate excitatory neurotransmission in the central nervous system and play key roles in brain development and disease. iGluRs have two distinct extracellular domains, but the functional role of the distal N-terminal domain (NTD) is poorly understood. Crystal structures of the NTD from some non-N-methyl-d-aspartate (NMDA) iGluRs are consistent with a rigid body that facilitates receptor assembly but suggest an additional dynamic role that could modulate signaling. Here, we moved beyond spatial and temporal limitations of conventional protein single-molecule spectroscopy by employing correlation analysis of extrinsic oxazine fluorescence fluctuations. We observed nanosecond (ns)-to-microsecond (μs) motions of loop segments and helices within a region of an AMPA-type iGluR NTD, which has been identified previously to be structurally variable. Our data reveal that the AMPA receptor NTD undergoes rapid conformational fluctuations, suggesting an inherent allosteric capacity for this domain in addition to its established assembly function.