Effects of Frequent Mowing on Survival and Persistence of Forbs Seeded into a Species-Poor Grassland

Many early attempts at tallgrass prairie reconstruction failed to achieve the high species diversity of remnant prairies, and instead consist primarily of C₄ grasses. We hypothesized that frequent mowing of established prairie grasses could create sufficient gaps in the aboveground and belowground environment to allow for the establishment of native forbs from seed. We studied forb seedling establishment in a 25‐year‐old prairie planting in northern Iowa that was dominated by native warm‐season grasses. In winter 1999, 23 species of native forbs were broadcast into the recently burned sod at a rate of 350 viable seeds/m². Treatment plots were mowed weekly for either one or two growing seasons, and control plots were unmowed. Mowed plots had greater light availability than controls, especially when warm‐season grasses began to flower. Overwinter seedling mortality was 3% in mowed treatments compared to 29% in the controls. Forbs in mowed plots had significantly greater root and shoot mass than those in control plots in the first and second growing seasons but were not significantly more abundant. By the fourth growing season, however, forbs were twice as abundant in the mowed treatments. No lasting negative impacts of frequent mowing on the grass population were observed. Mowing a second year influenced species composition but did not change total seedling establishment. Experimental evidence is consistent with the idea that mowing reduced competition for light from large established grasses, allowing forb seedlings the opportunity to reach sufficient size to establish, survive, and flower in the second and subsequent years.     

Terraced self assembled nano-structures from laminarin

The formation of self assembled nano-structures from the biopolymer laminarin dried onto mica is reported. The observed structures are composed of stacked terraced layers decreasing in size away from the mica surface. The layers display a high degree of dimensional regularity as observed using atomic force microscope imaging (AFM). The width of the layers is linearly dependent upon the number of layers in the structure and decreases with layer number away from the mica substrate. The thickness of the layers is uniform throughout the structure. A pore is contained in the central region of each structure with more than one layer. We postulate that these structures have potential use as templates in microelectronic devices and sensors where the central pore has the potential to immobilise functional materials.     

Rapid detection of human fecal contamination in estuarine environments by PCR targeting of Bifidobacterium adolescentis

Detection of Bifidobacterium adolescentis was used as an effective genetic marker of human fecal contamination in Georgia estuaries. Enterococci enumerations on mEI media indicated that a tributary to the Little Satilla River with 516 CFU/100 ml was the most polluted of all the rivers tested. Extracted DNA from eight river water samples was subjected to a two-step nested PCR protocol using genus and species specific primers for Bifidobacterium spp. and B. adolescentis. B. adolescentis was detected from extracted DNA in Dunbar River, Black Bank Creek, and in a Little Satilla River tributary which demonstrates the presence of human fecal contamination in these three rivers. In the five other estuaries tested including West Point-Federica River and the Altamaha River, which both had less than 16 CFU/100 ml of enterococci, B. adolescentis was not detected.     

A novel mode of action for a microbial-derived immunotoxin: the cytolethal distending toxin subunit B exhibits phosphatidylinositol 3,4,5-triphosphate phosphatase activity

The Actinobacillus actinomycetemcomitans cytolethal distending toxin (Cdt) is a potent immunotoxin that induces G(2) arrest in human lymphocytes. We now show that the CdtB subunit exhibits phosphatidylinositol (PI)-3,4,5-triphosphate phosphatase activity. Breakdown product analysis indicates that CdtB hydrolyzes PI-3,4,5-P(3) to PI-3,4-P(2) and therefore functions in a manner similar to phosphatidylinositol 5-phosphatases. Conserved amino acids critical to catalysis in this family of enzymes were mutated in the cdtB gene. The mutant proteins exhibit reduced phosphatase activity along with decreased ability to induce G(2) arrest. Consistent with this activity, Cdt induces time-dependent reduction of PI-3,4,5-P(3) in Jurkat cells. Lymphoid cells with defects in SHIP1 and/or ptase and tensin homolog deleted on chromosome 10 (PTEN) (such as Jurkat, CEM, Molt) and, concomitantly, elevated PI-3,4,5-P(3) levels were more sensitive to the toxin than HUT78 cells which contain functional levels of both enzymes and low levels of PI-3,4,5-P(3). Finally, reduction of Jurkat cell PI-3,4,5-P(3) synthesis using the PI3K inhibitors, wortmannin and LY290004, protects cells from toxin-induced cell cycle arrest. Collectively, these studies show that the CdtB not only exhibits PI-3,4,5-P(3) phosphatase activity, but also that toxicity in lymphocytes is related to this activity.     

HP1alpha guides neuronal fate by timing E2F-targeted genes silencing during terminal differentiation

A critical step of neuronal terminal differentiation is the permanent withdrawal from the cell cycle that requires the silencing of genes that drive mitosis. Here, we describe that the alpha isoform of the heterochromatin protein 1 (HP1) protein family exerts such silencing on several E2F-targeted genes. Among the different isoforms, HP1alpha levels progressively increase throughout differentiation and take over HP1gamma binding on E2F sites in mature neurons. When overexpressed, only HP1alpha is able to ensure a timed repression of E2F genes. Specific inhibition of HP1alpha expression drives neuronal progenitors either towards death or cell cycle progression, yet preventing the expression of the neuronal marker microtubule-associated protein 2. Furthermore, we provide evidence that this mechanism occurs in cerebellar granule neurons in vivo, during the postnatal development of the cerebellum. Finally, our results suggest that E2F-targeted genes are packaged into higher-order chromatin structures in mature neurons relative to neuroblasts, likely reflecting a transition from a 'repressed' versus 'silenced' status of these genes. Together, these data present new epigenetic regulations orchestrated by HP1 isoforms, critical for permanent cell cycle exit during neuronal differentiation.     

Effects of host migration, diversity and aquaculture on sea lice threats to Pacific salmon populations

Animal migrations can affect disease dynamics. One consequence of migration common to marine fish and invertebrates is migratory allopatry-a period of spatial separation between adult and juvenile hosts, which is caused by host migration and which prevents parasite transmission from adult to juvenile hosts. We studied this characteristic for sea lice (Lepeophtheirus salmonis and Caligus clemensi) and pink salmon (Oncorhynchus gorbuscha) from one of the Canada's largest salmon stocks. Migratory allopatry protects juvenile salmon from L. salmonis for two to three months of early marine life (2-3% prevalence). In contrast, host diversity facilitates access for C. clemensi to juvenile salmon (8-20% prevalence) but infections appear ephemeral. Aquaculture can augment host abundance and diversity and increase parasite exposure of wild juvenile fish. An empirically parametrized model shows high sensitivity of salmon populations to increased L. salmonis exposure, predicting population collapse at one to five motile L. salmonis per juvenile pink salmon. These results characterize parasite threats of salmon aquaculture to wild salmon populations and show how host migration and diversity are important factors affecting parasite transmission in the oceans.     

Plant availability of nutrients recovered as solids from human urine tested in climate chamber on Triticum aestivum L

Recovered nutrients by freezing-thawing from human urine in combination with struvite precipitation and nitrogen adsorption on zeolite and activated carbon have been tested in pot trials with wheat, Triticum aestivum L., in a climate chamber during 21 days. A simple test design using sand as substrate was chosen to give a first, general evaluation of the nutrient (P and N) availability from these sources. Dry weight, plant growth morphology, total-P and total-N were analysed. The tests show a slow-release of nutrients (P and N) from struvite and from N-adsorbents. The nitrogen in all treatments was in the deficiency range for optimum yield for wheat. Higher pH than usual for soil tests contributed to the difficulties in plant uptake, especially in the pots with only struvite (with highest MgO addition) as nutrient source.     

Development of potent, orally active 1-substituted-3,4-dihydro-2-quinolone glycogen phosphorylase inhibitors

A series of substituted 3,4-dihydro-2-quinolone glycogen phosphorylase inhibitors, which have potential as antidiabetic agents, is described. Initial members of the series showed good enzyme inhibitory potency but poor physical properties. Optimisation of the 1-substituent led to 2,3-dihydroxypropyl compounds which showed good in vitro potency and improved physical properties, together with good DMPK profiles and acute in vivo efficacy in a rat model. X-ray crystallographic data are presented, showing an unexpected variety of binding orientations at the dimer interface site.     

Radiolabeled divalent peptidomimetic vitronectin receptor antagonists as potential tumor radiotherapeutic and imaging agents

The integrin receptor alphavbeta3 is overexpressed on the endothelial cells of growing tumors and on some tumor cells themselves. A radiolabeled alphavbeta3 antagonists belonging to the quinolin-4-one class of peptidomimetics (TA138) was previously shown to exhibit high affinity for integrin alphavbeta3 and high selectivity versus other integrin receptors. 111In-TA138 exhibited high tumor uptake in the c-neu Oncomouse mammary adenocarcinoma model and produced excellent scintigraphic images. This study describes the synthesis of eight divalent versions of TA138 and their evaluation as potential tumor radiotherapeutic agents. The two main variables in this study were the length of the spacer bridging the biotargeting moieties and the total negative charge of the molecules imparted by the cysteic acid pharmacokinetic modifiers. Receptor affinity was evaluated in a panel of integrin receptor affinity assays, and biodistribution studies using the 111In-labeled derivatives were carried out in the c-neu Oncomouse model. All divalent agents maintained the high receptor affinity and selectivity of TA138, and six of the eight 111In derivatives exhibited blood clearance that was faster than 111In-TA138 at 24 h postinjection (PI). All divalent agents exhibited tumor uptake and retention at 24 h PI that was higher than 111In-TA138. Tumor/organ ratios were improved for most of the divalent agents at 24 h PI in critical nontarget organs marrow, kidney, and liver, with the agents having intermediate-length spacers (29-43 A) showing the largest improvement. As an example, 111In-15 showed tumor uptake of 14.3% ID/g at 24 h PI and tumor/organ ratios as follows: marrow, 3.24; kidney, 7.29; liver, 8.51. A comparison of therapeutic indices for 90Y-TA138 and 177Lu-15 indicate an improved therapeutic index for the divalent agent. The implications for radiotherapeutic applications and the mechanism of this multivalent effect are discussed.