Interactive effects of soil nitrogen and atmospheric carbon dioxide on root/rhizosphere carbon dioxide efflux from loblolly and ponderosa pine seedlings

We measured CO₂ efflux from intact root/rhizosphere systems of 155 day old loblolly (Pinus taeda L.) and ponderosa (Pinus ponderosa Dougl. ex Laws.) pine seedlings in order to study the effects of elevated atmospheric CO₂ on the below-ground carbon balance of coniferous tree seedlings. Seedlings were grown in sterilized sand culture, watered daily with either 1, 3.5 or 7 mt M NH ₄ ⁺ , and maintained in an atmosphere of either 35 or 70 Pa CO₂. Carbon dioxide efflux (mol CO₂ plant^–1 s^–1) from the root/rhizosphere system of both species significantly increased when seedlings were grown in elevated CO₂, primarily due to large increases in root mass. Specific CO₂ efflux (mol CO₂ g root^–1 s^–1) responded to CO₂ only under conditions of adequate soil nitrogen availability (3.5 mt M). Under these conditions, CO₂ efflux rates from loblolly pine increased 70% from 0.0089 to 0.0151 mol g^–1 s^–1 with elevated CO₂ while ponderosa pine responded with a 59% decrease, from 0.0187 to 0.0077 mol g^–1 s^–1. Although below ground CO₂ efflux from seedlings grown in either sub-optimal (1 mt M) or supra-optimal (7 mt M) nitrogen availability did not respond to CO₂, there was a significant nitrogen treatment effect. Seedlings grown in supra-optimal soil nitrogen had significantly increased specific CO₂ efflux rates, and significantly lower total biomass compared to either of the other two nitrogen treatments. These results indicate that carbon losses from the root/rhizosphere systems are responsive to environmental resource availability, that the magnitude and direction of these responses are species dependent, and may lead to significantly different effects on whole plant carbon balance of these two forest tree species.     

Extracellular matrix-resident basic fibroblast growth factor: implication for the control of angiogenesis.

Despite the ubiquitous presence of basic fibroblast growth factor (bFGF) in normal tissues, endothelial cell proliferation in these tissues is usually very low, suggesting that bFGF is somehow sequestered from its site of action. Immunohistochemical staining revealed the localization of bFGF in basement membranes of diverse tissues, suggesting that the extracellular matrix (ECM) may serve as a reservoir for bFGF. Moreover, functional studies indicated that bFGF is an ECM component required for supporting endothelial cell proliferation and neuronal differentiation. We have found that bFGF is bound to heparan sulfate (HS) in the ECM and is released in an active form when the ECM-HS is degraded by heparanase expressed by normal and malignant cells (i.e. platelets, neutrophils, lymphoma cells). It is proposed that restriction of bFGF bioavailability by binding to ECM and local regulation of its release provide a novel mechanism for neovascularization in normal and pathological situations. The subendothelial ECM contains also tissue type- and urokinase type-plasminogen activators which participate in cell invasion and tissue remodeling. These results and studies on the properties of other ECM-immobilized enzymes (i.e. thrombin, plasmin, lipoprotein lipase) and growth factors (GM-CSF, IL-3, osteogenin), suggest that the ECM provides a storage depot for biologically active molecules which are thereby stabilized and protected. This may allow a more localized and persistent mode of action, as compared to the same molecules in a fluid phase.     

Efficient new ribozyme mimics: direct mapping of molecular design principles from small molecules to macromolecular, biomimetic catalysts

Dramatic improvements in ribozyme mimics have been achieved by employing the principles of small molecule catalysis to the design of macromolecular, biomimetic reagents. Ribozyme mimics derived from the ligand 2,9-dimethylphenanthroline (neocuproine) show at least 30-fold improvements in efficiency at sequence-specific RNA cleavage when compared with analogous o-phenanthroline- and terpyridine-derived reagents. The suppression of hydroxide-bridged dimers and the greater activation of coordinated water by Cu(II) neocuproine (compared with the o-phananthroline and terpyridine complexes) better allow Cu(II) to reach its catalytic potential as a biomimetic RNA cleavage agent. This work demonstrates the direct mapping of molecular design principles from small-molecule cleavage to macromolecular cleavage events, generating enhanced biomimetic, sequence-specific RNA cleavage agents.     

Developing indices of relative abundance for monitoring cave and ground wētā (Orthoptera) in southern beech forest,New Zealand

We sampled populations of forest-floor dwelling cave and ground wētā using footprint tracking tunnels and spotlight transect counts in southern beech forest, New Zealand. Samples were compared to estimates of wētā density based on mark–recapture estimates from 25?m² enclosures. Both activity indices captured variability in cave wētā in time and space, were strongly correlated with each other, and have the potential for monitoring cave wētā activity levels. Comparisons between indices and cave wētā density estimates were equivocal, as recapture rates were too low to calculate high-resolution density estimates. We also found that cave wētā counts had a curved relationship increasing with temperature, and a negative relationship with increasing shrub and woody debris cover. Based on these preliminary results, tracking tunnels could be a viable method of monitoring cave wētā as they appear more efficient than transect counts and are relatively inexpensive. However, further calibration trials are needed to determine if indices mirror robust population density estimates.     

The role of calcium cations in the mechanism of phytochrome-dependent regulation of the <Emphasis Type="Italic">sdh1-2</Emphasis> gene expression and succinate dehydrogenase activity in maize leaves

The regulation of succinate dehydrogenase (SDH) activity and its gene expression by the phytochrome system has been demonstrated: red light (660 nm) reduces the SDH activity and the level of expression of the sdh1-2 gene. At the same time, the content of calcium cations in the nuclear fraction increases; it seems to be one of the mechanisms of phytochrome signal transduction in plant cells. Far-red light (730 nm) had opposite effects, i.e., increased SDH activity and the level of expression of the sdh1-2 gene. The data suggest that the SDH activity can be regulated at the level of expression in the green leaves of Zea mays by the phytochrome system with the involvement of calcium ions as a signal transduction messenger.     

The histone core exerts a dominant constraint on the structure of DNA in a nucleosome.

We have examined the structures of unique sequence, A/T-rich DNAs that are predicted to be relatively rigid [oligo(dA).oligo(dT)], flexible [oligo[d(A-T)]], and curved, using the hydroxyl radical as a cleavage reagent. A 50-base-pair segment containing each of these distinct DNA sequences was placed adjacent to the T7 RNA polymerase promoter, a sequence that will strongly position nucleosomes. The final length of the DNA fragments was 142 bp, enough DNA to assemble a single nucleosome. Cleavage of DNA in solution, while bound to a calcium phosphate crystal, and after incorporation into a nucleosome is examined. We find that the distinct A/T-rich DNAs have very different structural features in solution and helical periodicities when bound to a calcium phosphate. In contrast, the organization of the different DNA sequences when associated with a histone octamer is very similar. We conclude that the histone core exerts a dominant constraint on the structure of DNA in a nucleosome and that inclusion of these various unique sequences has only a very small effect on overall nucleosome stability and structure.     

Synthesis and evaluation of RNA transesterification efficiency using stereospecific serinol-terpyridine conjugates

Six novel artificial ribonucleases were synthesized employing a stereochemically pure abasic serinol backbone residue for attachment of the RNA transesterification agent copper(II) terpyridine. These stereochemically pure abasic residues were synthesized as phosphoramidite building blocks from the parent L-serine and D-serine starting building blocks and incorporated into oligonucleotides via solid-phase DNA synthesis. These artificial ribonucleases were constructed to determine if the stereochemistry of the alpha carbon of an abasic serinol residue has influence over RNA transesterification through selective placement of a pendant transesterification agent in either the major or minor groove. The novel artificial ribonucleases and previously synthesized artificial ribonucleases were challenged with a 28-mer and 159-mer RNA substrate. It was determined that the stereochemistry of the carbon atom derived from the alpha-carbon of serine did not influence the extent of cleavage in these studies using copper(II) terpyridine conjugated artificial ribonucleases.