Phenological response of tundra plants to background climate variation tested using the International Tundra Experiment.

The rapidly warming temperatures in high-latitude and alpine regions have the potential to alter the phenology of Arctic and alpine plants, affecting processes ranging from food webs to ecosystem trace gas fluxes. The International Tundra Experiment (ITEX) was initiated in 1990 to evaluate the effects of expected rapid changes in temperature on tundra plant phenology, growth and community changes using experimental warming. Here, we used the ITEX control data to test the phenological responses to background temperature variation across sites spanning latitudinal and moisture gradients. The dataset overall did not show an advance in phenology; instead, temperature variability during the years sampled and an absence of warming at some sites resulted in mixed responses. Phenological transitions of high Arctic plants clearly occurred at lower heat sum thresholds than those of low Arctic and alpine plants. However, sensitivity to temperature change was similar among plants from the different climate zones. Plants of different communities and growth forms differed for some phenological responses. Heat sums associated with flowering and greening appear to have increased over time. These results point to a complex suite of changes in plant communities and ecosystem function in high latitudes and elevations as the climate warms.

Temperature dependence for fluorescence of beta-NADH in glycerol/water solution and in trehalose/sucrose glass.

Fluorescence imaging of cells and tissue can be used to evaluate beta-NADH redox and location. At low temperature, beta-NADH fluorescence intensity increases and therefore sensitivity of imaging increases. In this paper, the temperature dependence of fluorescence was evaluated for beta-NADH in glycerol/water solution and in trehalose/sucrose glass. The average fluorescence lifetime for NADH in glycerol/water is 0.66 ns, compared with 5.3 ns in trehalose/ sucrose at 20 degrees C. Emission spectra were recorded from 290 to 12 K. The fluorescence of beta-NADH in glycerol/water increases approximately 16 fold and the emission shifts about 35 nm to the blue as temperature decreases. Much smaller change is seen for fluorescence of beta-NADH in sugar glass. Below 77 K, the beta-NADH spectral features did not change significantly with temperature change, and so no increase in sensitivity is obtained by going to very low temperatures. It is suggested that the sensitivity of beta-NADH fluorescence is related to water relaxation around the excited state molecule. Differences in water in various tissues may contribute to beta-NADH fluorescence changes when cells are altered.

SRA880, in vitro characterization of the first non-peptide somatostatin sst(1) receptor antagonist.

This report describes the in vitro features of the first somatostatin sst(1) receptor selective non-peptide antagonist, SRA880 ([3R,4aR,10aR]-1,2,3,4,4a,5,10,10a-Octahydro-6-methoxy-1-methyl-benz[g] quinoline-3-carboxylic-acid-4-(4-nitro-phenyl)-piperazine-amide, hydrogen malonate). SRA was evaluated in a number of in vitro systems of various species, both at native and recombinant receptors, using radioligand binding and second messenger/transduction studies. SRA880 has high affinity for native rat, mouse, monkey and human cerebral cortex somatostatin sst(1) receptors (pK(d) = 7.8-8.6) and for human recombinant sst(1) receptors (pK(d) = 8.0-8.1). SRA880 displayed significantly lower affinity for the other human recombinant somatostatin receptors ( pK(d) < or = 6.0) or a wide range of neurotransmitter receptors, except for the human dopamine D4 receptors. SRA880 was characterized in various transduction assays: somatotropin release inhibiting factor (SRIF) induced inhibition of forskolin-stimulated cAMP accumulation, SRIF stimulated-GTPgammaS binding, and SRIF stimulated luciferase gene expression; in all tests, SRA880 was devoid of intrinsic activity and acted as an apparently surmountable antagonist with pK(B) values of 7.5-7.7. Combined with the data from binding studies, these results suggest that SRA880 acts as a competitive antagonist. Thus, SRA880 is the first non-peptide somatostatin sst(1) receptor antagonist to be reported; SRA880 will be a useful tool for the characterization of somatostatin sst(1) receptor-mediated effects both in vitro and in vivo.