Decomposition and nutrient dynamics of oak Quercus spp. logs after five years of decomposition

Decomposition of oak Quercus spp. logs (25 35 cm diameter, 3 m long) was compared among log substrates in Oregon, Minnesota. Kansas and North Carolina during the first five years on the ground. Decomposition of whole logs (weighted by substrate) averaged 0.069 yr^-1 (±0.16 SD). but followed a 2-exponential model (k = 0.12 yr^-1 year 1 and k = 0.06 yr ^-1 years 2 5), reflecting qualitative differences among log substrates (outer and inner bark, sapwood and heartwood). Rapid loss from bark substrates contributed to the initial rapid decay rate. Sapwood decay rate averaged 0.15 yr^-1 and dominated the second log decay rate. Heartwood lost only 6% mass during the first five years, for an overall decay rate of 0.012 yr^-1 that likely will represent a longer-term third exponential decay rate.
Carbon loss amounted to ca 5 kg yr^-1 per 170 kg log. Nutrient concentrations generally declined during the first five years, but nitrogen, sulfur, and sodium accumulated in sapwood and heartwood during this period. Sulfur content increased in all substrates and doubled in whole logs during this 5-yr period. Complex patterns of nutrient content suggest patterns of microbial colonization and nutrient utilization. Polynomial models were developed to describe rates of carbon and nutrient flux in log substrates.     

On the optimal sex-ratio: A stability analysis based on a characterization for one-locus multiallele viability models

Theoretical one-locus multiallele sex-determination models are found to admit even sex ratio equilibrium surfaces besides the equilibria for corresponding one-locus multiallele viability models. Both types of equilibria can be defined in terms of a single spectral radius function, the former corresponding to level surfaces and the latter to critical points. The stable equilibria in the corresponding viability models are associated with the local maxima, and the equilibrium structures for the sex-determination models can be fully described. Several optimality properties of the even-sex-ratio equilibrium surfaces can be deduced.Supported in part by NIH Grant 5R01 GM10452-20 and NSF Grant MCS79-24310     

Frequency-dependent regulation of cardiac Na(+)/Ca(2+) exchanger

The activity of the cardiac Na(+)/Ca(2+) exchanger (NCX1.1) undergoes continuous modulation during the contraction-relaxation cycle because of the accompanying changes in the electrochemical gradients for Na(+) and Ca(2+). In addition, NCX1.1 activity is also modulated via secondary, ionic regulatory mechanisms mediated by Na(+) and Ca(2+). In an effort to evaluate how ionic regulation influences exchange activity under pulsatile conditions, we studied the behavior of the cloned NCX1.1 during frequency-controlled changes in intracellular Na(+) and Ca(+) (Na(i)(+) and Ca(i)(2+)). Na(+)/Ca(2+) exchange activity was measured by the giant excised patch-clamp technique with conditions chosen to maximize the extent of Na(+)- and Ca(2+)-dependent ionic regulation so that the effects of variables such as pulse frequency and duration could be optimally discerned. We demonstrate that increasing the frequency or duration of solution pulses leads to a progressive decline in pure outward, but not pure inward, Na(+)/Ca(2+) exchange current. However, when the exchanger is permitted to alternate between inward and outward transport modes, both current modes exhibit substantial levels of inactivation. Changes in regulatory Ca(2+), or exposure of patches to limited proteolysis by alpha-chymotrypsin, reveal that this "coupling" is due to Na(+)-dependent inactivation originating from the outward current mode. Under physiological ionic conditions, however, evidence for modulation of exchange currents by Na(i)(+)-dependent inactivation was not apparent. The current approach provides a novel means for assessment of Na(+)/Ca(2+) exchange ionic regulation that may ultimately prove useful in understanding its role under physiological and pathophysiological conditions.     

Diverse heterocyclic scaffolds as dCTP pyrophosphatase 1 inhibitors. Part 1: Triazoles,triazolopyrimidines, triazinoindoles,quinoline hydrazones and arylpiperazines

A high-throughput screening campaign using a commercial compound library (ChemBridge DiverSET) revealed diverse chemotypes as inhibitors of the human dCTP pyrophosphatase 1 (dCTPase). Triazole, triazolopyrimidine, triazinoindole, quinoline hydrazone and arylpiperazine hits were clustered, confirmed by IC₅₀ determinations, and their preliminary structure-activity-relationships (SAR) and ligand efficiency scores are discussed in this letter.     

Fixation probability with multiple alleles and projected average allelic effect on selection

The first-order effect of selection on the probability of fixation of an allele, with respect to an intensity of selection s>0 in a diploid population of fixed finite size N, undergoing discrete, non-overlapping generations, is shown to be given by the sum of the average effects of that allele on the coefficient of selection in the current generation and all future generations, given the population state in the current generation. This projected average allelic effect is a weighted sum of average allelic effects in allozygous and autozygous offspring in the initial generation, with weights given in terms of expected coalescence times, under neutrality, for the lineages of two or three gametes chosen at random in the same generation. This is shown in the framework of multiple alleles at one locus, with genotypic values determining either viability or fertility differences, and with either multinomial or exchangeable reproduction schemes. In the limit of weak selection in a large population such that Ns tends to zero, the initial average allelic effects in allozygous offspring and autozygous offspring have the same weight on the fixation probability only in the domain of application of the Kingman coalescent. With frequency-dependent selection in a linear-game-theoretic context with two phenotypes determined by additive gene action, the first-order effect on the fixation probability is a combination of two effects of frequency-independent selection, one in a haploid population, the other in a diploid population. In the domain of application of the Kingman coalescent as the population size goes to infinity and Ns to zero, the first effect is three times more important than the second effect. This explains the one-third law of evolutionary dynamics in this domain, and shows how this law can be extended beyond this domain.     

Ex Vivo Culture of Patient Tissue & Examination of Gene Delivery

This video describes the use of patient tissue as an ex vivo model for the study of gene delivery. Fresh patient tissue obtained at the time of surgery is sliced and maintained in culture. The ex vivo model system allows for the physical delivery of genes into intact patient tissue and gene expression is analysed by bioluminescence imaging using the IVIS detection system. The bioluminescent detection system demonstrates rapid and accurate quantification of gene expression within individual slices without the need for tissue sacrifice. This slice tissue culture system may be used in a variety of tissue types including normal and malignant tissue and allows us to study the effects of the heterogeneous nature of intact tissue and the high degree of variability between individual patients. This model system could be used in certain situations as an alternative to animal models and as a complementary preclinical mode prior to entering clinical trial.Download video file.^{(23M, mov)}