An analysis of climate and competition as contributors to decline of red spruce in high elevation Appalachian forests of the Eastern United states

Summary Long-term growth patterns of red spruce (Picea rubens Sarg.) were analyzed from increment cores collected from over 1000 trees at 48 sites in the eastern United States. Principal objectives were the evaluation of the distribution, timing, and uniqueness of observed patterns of decreasing radial growth during the past 25 years and the examination of stand competition and climate as factors contributing to observed changes.Our analyses focused on historical records of spruce mortality and approximately 200 years of radial growth data to search for historical precedents for current trends. In this work we have used time series analysis to detect the temporal frequency of significant negative or positive shifts in radial growth rates, an analysis of relationships between a stand competition index and observed changes in growth and mortality, and modeling of past growth-climate relationships to determine whether recent growth changes could be predicted based on climate.Collectively, these analyses indicate that the observed growth decreases of surviving red spruce trees at northeastern sites with high mortality have been anomalous during the past 20 to 25 years with respect to both historical annual growth patterns and past relationships to climate or stand development at these sites. In general, reductions in radial increment that have also been noted at southern high elevation sites but not at low elevations occurred 5 to 10 years later than at northern sites and represent less substantive departures from growth trends predicted by linear climate models.These results suggest that regional and not local stresses have triggered the observed decline in radial growth of red spruce at these sites. While climatic change may have contributed to observed changes, the degree of radial growth suppression observed is greater than would be expected based on past growth-climate relationships. This unique relationship of growth to climate suggests the influences of either recent, unique combinations of climatic stresses or the possibly interactive intervention of other regional-scale stresses, such as atmospheric pollution.Although the research described in this article has been funded wholly or in part by the United States Environmental Protection Agency (EPA) through Interagency Agreement Number DW 89931334-01-0 with the U.S. Department of Energy, it has not been subjected to EPA review and therefore does not necessarily reflect the views of EPA, and no official endorsement should be inferred     

Interactions between the trp repressor and its operator sequence as studied by base analogue substitution.

A series of modified trp operator sequences has been prepared by the incorporation of seven different base analogues. Four of the analogues allow the site-specific deletion of functional groups present on the dA-dT and dT-dA base pairs at positions -4/+4 and -5/+5 in the trp operator. The remaining three analogues permit the incorporation of structural analogues of the native dA-dT or dG-dC base pairs. The duplex operator sequences all exhibit Tm values well above ambient temperature (48-70 degrees C), and these values generally correlate very well with the number of interstrand hydrogen bonds present. The affinity between the trp repressor and 14 modified operator sequences was examined using a recently developed alkaline phosphatase protection assay. The results from the analogue sequences used in this study suggest that the structure of the dA-dT or dT-dA base pairs at positions -4/+4 and -5/+5, respectively, has relatively little effect upon the solution binding by the trp repressor, but the protein is very sensitive to the orientation of the amino and carbonyl functional groups at the -4/+4 positions, which are involved in the formation of an interbase hydrogen bond present in the major groove. (The term structure in this case refers to the hydrogen bonding structure of the base pairs. We recognize that the introduction of conservative functional group deletions or reversals may affect other structural criteria such as hydration.) The deletion of individual functional groups from the operator sequence suggests that the carbonyl at dT+4 is critical for formation of the high-affinity sequence-specific complex. Additionally, the thymine methyl group at dT+4 and the N7 nitrogen of dA+5 appear to be critical contacts necessary for high-affinity binding by the repressor. The thymine carbonyl and the adenine N7 nitrogen are each responsible for approximately -1.5 kcal/mol of apparent free energy of binding. The thymine methyl provides a somewhat smaller contribution of -0.7 kcal/mol. Deletion of either of the adenine amino groups at dA-4 or dA+5 results in a sequence that binds to the repressor with a higher affinity than observed with the native sequence; this can be explained in that the functional groups lost are not critical for binding, and the resulting increased flexibility of the operator, or the creation of a more hydrophobic surface at these sites, enhances van der Waals contacts between the protein and the nucleic acid.     

Effects of voltage clamping on epithelial cell composition in toad urinary bladder studied with X-ray microanalysis

Toad urinary bladder epithelial cells were incubated in Na Ringer's with the serosal surface of the epithelium clamped at either +50 mV, O mV (short-circuited) or –50 mV with respect to the mucosal surface. Following incubation, portions of tissue were coated with an external albumin standard and rapidly frozen. Cryosections were freeze-dried and cell composition determined by x-ray microanalysis. Cell water and ion contents were unaffected when tissues were short-circuited rather than clamped close to their open-circuit potential difference (+50 mV). Incubation with vasopressin at +50 mV, and under short-circuit conditions, caused Na uptake without cell swelling or gain in Cl. Clamping at –50 mV resulted in uptake of water and ions, with considerable variation from cell to cell. These variations in cell composition were exacerbated by vasopressin. The greater the increase in water content, the greater the rise in cell Cl. However, there was no consistent pattern to the associated changes in cation contents. Most cells gained some Na. In some cells, this gain was accompanied by an increase in K. In others, the gain of Na was predominant and cell K content actually fell. At –50 mV with ouabain, many of the cells also gained water. As was found in our earlier study with ouabain under short circuit conditions (Bowler et al., 1991), there was considerable variation in the extent of the Na gain and K loss; some cells were largely depleted of K while in others the K content remained relatively normal. These results indicate differences between granular cells in the availabilities in the plasma membranes of ion pathways, either as a consequence of differences in the numbers of such pathways or in their control.This work was supported by a grant from the Health Research Council of New Zealand. Purchase of the equipment was made possible through grants from the Medical Research Council of New Zealand, the Medical Distribution Committee of the Lottery Board, the University Grants Committee, the Telford Trust, the New Zealand Neurological Foundation and the National Heart Foundation. We are grateful for the excellent technical assistance of Ms. S. Zellhuber-McMillan.     

Duration of opiate receptor blockade determines tumorigenic response in mice with neuroblastoma: a role for endogenous opioid systems in cancer

The relationship between the pharmacological properties of an opioid antagonist, naltrexone (NTX), and tumor response was studied in mice with transplanted neuroblastoma (NB). Animals receiving 0.1 mg/kg NTX every 6 hr, which blocked morphine-induced analgesia for 24 hr each day, had a 100% tumor incidence, no deviation in time before tumor appearance, and a 17% decrease from control values in total survival time. In contrast, once daily injections of either 0.1 mg/kg NTX or 0.4 mg/kg NTX (the equivalent of 0.1 mg/kg given 4 times daily), which blocked morphine-induced analgesia for less than 10 hr each day, resulted in a tumor incidence of 20% and 60%, respectively, delays in time prior to tumor appearance of 90% and 65%, respectively, and an increased total survival time of 10% and 24%, respectively, for tumor-bearing mice relative to control levels. Inoculation of NB in control animals resulted in 100% tumor appearance within 16 days and a mean survival time of 36 days. These results show that tumorigenic events are dictated by the duration of opiate receptor blockade rather than the dosage of opiate antagonist, and provide compelling evidence that endogenous opioid systems play a crucial role in neuro-oncogenic expression.