Vegetative and edaphic characteristics on relic charcoal hearths in the Appalachian mountains

Relic charcoal hearths are prevalent throughout the Appalachian Mountains as reminders of the wood charcoal era and are evident today by the characteristics of forest stand structure, composition and understory vegetation. The importance of the soil resource to the stability and recovery of these anomalies in the plant community is not well understood. This study was conducted to compare forest floor and soil chemical properties, and vegetative characteristics on relic charcoal hearths to adjacent, non-hearth areas. Overstory tree cover and density was significantly lower on hearths than for adjacent areas. Overstory richness and diversity were consistently, but not significantly, lower on hearths, as were density and species richness of understory and ground vegetation. Little difference between hearth and adjacent forest floor properties was observed; however, soil calcium concentrations, pH. and percent carbon were higher on hearths, and phosphorus concentrations were generally lower. We discuss the effects of releasing large amounts of base-forming cations through repeated use of the hearths and the subsequent long-term effects on soil fertility and vegetative development.     

Stomatal and nonstomatal limitations of photosynthesis in relation to the drought and shade tolerance of tree species in open and understory environments

 Light saturated photosynthesis (A) in field saplings of shade tolerant, intermediate, and intolerant tree species was analyzed for stomatal and nonstomatal limitations to test differences between species and sun and shade phenotypes during drought. Throughout the study, photosynthesis was highest and mesophyll limitations of A (L_m) lowest in the intolerant species in both open and understory habitats. The shade tolerant species exhibited the only drought-related decreased A and increased L_m in the open, and the greatest drought-related decreased A and increased L_m in the understory. Few species exhibited significant habitat or drought-related differences in stomatal conductance to CO₂ (g_c), but even slight decreases in g_c during drought were associated with large increases in stomatal limitations to A (L_g). Combined changes in L_m and L_g resulted in increased relative stomatal limitation to A (l _g) in several species during drought. Nevertheless, the overall lack of stomatal closure allowed for nonstomatal limitations to play a major role in reduced A during drought. Higher leaf N was associated with shallower slope of the l _g versus g_c relationship, an indication of greater A capacity. Photosynthetic capacity tended to be greater in the intolerant species than the tolerant species, and it tended to decrease during drought primarily in the shade tolerant species in the understory. Findings in the literature suggest that carbon reduction reactions may be more susceptible to drought than photosynthetic light reactions. If so, reduced carbon reduction capacity of shade tolerant species or shade phenotypes may predispose them to drought conditions, which suggests a mechanism behind the well-recognized tradeoff between drought tolerance and shade tolerance of temperate tree species. Received: 20 October 1995 / Accepted: 20 February 1996     

Viral RNA modulates the acid sensitivity of foot-and-mouth disease virus capsids.

Foot-and-mouth disease virus (FMDV) manifests an extreme sensitivity to acid, which is thought to be important for entry of the RNA genome into the cell. We have compared the low-pH-induced disassembly in vitro of virions and natural empty capsids of three subtypes of serotype A FMDV by enzyme-linked immunosorbent assay and sucrose gradient sedimentation analysis. For all three subtypes (A22 Iraq 24/64, A10(61), and A24 Cruzeiro), the empty capsid was more stable by 0.5 pH unit on average than the corresponding virion. Unexpectedly, in the natural empty capsids used in this study, the precursor capsid protein VP0 was found largely to be cleaved into VP2 and VP4. For picornaviruses the processing of VP0 is closely associated with encapsidation of viral RNA, which is considered likely to play a catalytic role in the cleavage. Investigation of the cleavage of VP0 in natural empty capsids failed to implicate the viral RNA. However, it remains possible that these particles arise from abortive attempts to encapsidate RNA. Empty capsids expressed from a vaccinia virus recombinant showed essentially the same acid lability as natural empty capsids, despite differing considerably in the extent of VP0 processing, with the synthetic particles containing almost exclusively uncleaved VP0. These results indicate that it is the viral RNA that modulates acid lability in FMDV. In all cases the capsids dissociate at low pH directly into pentameric subunits. Comparison of the three viruses indicates that FMDV A22 Iraq is about 0.5 pH unit more sensitive to low pH than types A10(61) and A24 Cruzeiro. Sequence analysis of the three subtypes identified several differences at the interface between pentamers and highlighted a His-alpha-helix dipole interaction which spans the pentamer interface and appears likely to influence the acid lability of the virus.     

Sources of stress among nurses: an empirical investigation

The effect of personality, demographic, and professional variables on nurses' experienced stress is examined through the use of the Nursing Stress Inventory in a midwestern Catholic hospital. Findings indicate that age, nursing role status, length of time since graduation, job tenure, area of nursing, and interpersonal needs are associated with various dimensions of stress.     

The contractile basis of amoeboid movement: V. The control of gelation, solation, and contraction in extracts from dictyostelium discoideum

Motile extracts have been prepared from Dictyostelium discoideum by homogenization and differential centrifugation at 4 degrees C in a stabilization solution (60). These extracts gelled on warming to 25 degrees Celsius and contracted in response to micromolar Ca++ or a pH in excess of 7.0. Optimal gelation occurred in a solution containing 2.5 mM ethylene glycol-bis (β-aminoethyl ether)N,N,N',N'-tetraacetate (EGTA), 2.5 mM piperazine-N-N'-bis [2-ethane sulfonic acid] (PIPES), 1 mM MgC1(2), 1 mM ATP, and 20 mM KCI at ph 7.0 (relaxation solution), while micromolar levels of Ca++ inhibited gelation. Conditions that solated the gel elicited contraction of extracts containing myosin. This was true regardless of whether chemical (micromolar Ca++, pH >7.0, cytochalasin B, elevated concentrations of KCI, MgC1(2), and sucrose) or physical (pressure, mechanical stress, and cold) means were used to induce solation. Myosin was definitely required for contraction. During Ca++-or pH-elicited contraction: (a) actin, myosin, and a 95,000-dalton polypeptide were concentrated in the contracted extract; (b) the gelation activity was recovered in the material sqeezed out the contracting extract;(c) electron microscopy demonstrated that the number of free, recognizable F-actin filaments increased; (d) the actomyosin MgATPase activity was stimulated by 4- to 10-fold. In the absense of myosin the Dictyostelium extract did not contract, while gelation proceeded normally. During solation of the gel in the absense of myosin: (a) electron microscopy demonstrated that the number of free, recognizable F- actin filaments increased; (b) solation-dependent contraction of the extract and the Ca++-stimulated MgATPase activity were reconstituted by adding puried Dictyostelium myosin. Actin purified from the Dictyostelium extract did not gel (at 2 mg/ml), while low concentrations of actin (0.7-2 mg/ml) that contained several contaminating components underwent rapid Ca++ regulated gelation. These results indicated : (a) gelation in Dictyostelium extracts involves a specific Ca++-sensitive interaction between actin and several other components; (b) myosin is an absolute requirement for contraction of the extract; (c) actin-myosin interactions capable of producing force for movement are prevented in the gel, while solation of the gel by either physical or chemical means results in the release of F-actin capable of interaction with myosin and subsequent contraction. The effectiveness of physical agents in producting contraction suggests that the regulation of contraction by the gel is structural in nature.     

Affinity labeling of 3 alpha-hydroxysteroid dehydrogenase with 3 alpha-bromoacetoxyandrosterone and 11 alpha-bromoacetoxyprogesterone. Isolation and sequence of active site peptides containing reactive cysteines; sequence confirmation using nucleotide sequence from a cDNA clone

Homogeneous 3 alpha-hydroxysteroid dehydrogenase (3 alpha-HSD, EC 1.1.1.50) of rat liver cytosol is potently inhibited at its active site by nonsteroidal anti-inflammatory drugs (NSAIDs). Using 3 alpha-bromoacetoxy-5 alpha-androstan-17-one (BrAnd, a substrate analog) and 11 alpha-bromoacetoxyprogesterone (Br11P, a glucocorticoid analog) as affinity-labeling agents, kinetic evidence was obtained that these agents alkylate this site. Inactivation of 3 alpha-HSD with either [14C]BrAnd or [14C] Br11P led to the incorporation of 1 mol of affinity-labeling agent per enzyme monomer. Complete acid hydrolysis of 3 alpha-HSD radiolabeled with either agent followed by amino acid analysis led to the identification of [14C]carboxymethylcysteine indicating that [14C]BrAnd and [14C]Br11P covalently tag discrete reactive cysteine(s) at the enzyme active site. Trypsin digestion of [14C]BrAnd-inactivated 3 alpha-HSD followed by peptide mapping led to the purification of a single radiolabeled peptide (3A1) which gave the following sequence: H2N-Ser-Ile-Gly-Val-Ser-Asn-Phe-Asn-X-Arg-CO2H. Identical experiments on [14C] Br11P-inactivated 3 alpha-HSD led to the purification of three radiolabeled peptides (11P1-11P3). The major radiolabeled peptide (11P1) had an identical sequence to 3A1 which was tagged with [14C]BrAnd. The minor radiolabeled peptides had the following sequences: H2N-Ser-Lys-Asp-Ile-Ile-Leu-Val-Ser-Tyr-X-Thr-Leu-Gly-Ser-Ser-Arg-CO2H (11P2) and H2N-Ser-Pro-Val-Leu-Leu-Asp-Asp-Pro-Val-Leu-X-Ala-Ile-Ala-Lys-CO2H (11P3). In each peptide group X was identified as carboxymethylcysteine. Alignment of the peptide sequences with the primary structure of 3 alpha-HSD, deduced from its cDNA clone, assigned peptide 11P1 to residues 162-171, peptide 11P2 to residues 208-223, and peptide 11P3 to residues 232-246 of the amino acid sequence. The reactive cysteines correspond to Cys170, Cys217, and Cys242. We propose that Cys170 labeled by BrAnd may lie within the catalytic pocket of the enzyme. By contrast the 11 alpha-bromoacetoxy group in Br11P labeled several reactive cysteines which may be involved in the binding of glucocorticoids and NSAIDs.     

Parallel regulation of IL-4 and IL-5 in human helminth infections.

To investigate the relationship between cytokine production and the increased levels of serum IgE and peripheral eosinophilia commonly accompanying human helminth infections, we studied the ability of PBMC of normal (N1) (n = 18) and eosinophilic individuals with helminth infections (H1) (n = 9) to produce IL-3, IL-4, IL-5, granulocyte-macrophage-CSF, and IFN-gamma in vitro after stimulation with PMA (50 ng/ml) and ionomycin (1 microgram/ml). The two groups differed in both the levels of serum IgE and eosinophilia. For mitogen-induced production of granulocyte-macrophage-CSF and IFN-gamma, there was no difference in cytokine production between the two groups. In marked contrast, supernatants from PBMC of infected individuals had significantly higher levels of IL-4 (mean = 213 pg/ml for N1 and 944 pg/ml for H1, p less than 0.02), IL-5 (mean = 180 pg/ml for N1 and 1118 pg/ml for HL, p less than 0.001), and IL-3 (mean = 13900 pg/ml for N1, 28029 pg/ml for H1, p less than 0.05). In addition, helminth-infected patients had approximately 5-fold greater numbers of T cells capable of producing IL-5 and 2.5-fold greater frequency of IL-4-secreting cells than did normal individuals; GM-CSF- and IFN-gamma-producing T cell numbers were not significantly different in the two groups. IL-3-producing cell frequencies could not be evaluated by this method. There was a direct correlation between IL-4 production and IL-5 production at the level of both protein production and frequency of T cells capable of producing these cytokines. These data indicate that individuals with reactive eosinophilia and elevated serum IgE have an expanded population of lymphocytes producing IL-4 and IL-5 and the association of the two suggests that the regulation of IL-4 and IL-5 may be linked.     

Optically pure abscisic Acid analogs-tools for relating germination inhibition and gene expression in wheat embryos

We report an examination of the structural requirements of the abscisic acid (ABA) recognition response in wheat dormant seed embryos using optically pure isomers of ABA analogs. These compounds include permutations to the ABA structure with either an acetylene or a trans bond at C-4 C-5, and either a single or double bond at the C-2′ C-3′ double bond. (R)-ABA and the three isomers with the same configuration at C-1′ as natural ABA were found to be effective germination inhibitors. The biologically active ABA analogs exhibited differential effects on ABA-responsive gene expression. All the ABA analogs that inhibited germination induced two ABA-responsive genes, wheat group 3 lea and dhn (rab). However, (R)-ABA and (S)-dihydroABA were less effective in inducing the ABA-responsive gene Em within the time that embryonic germination was inhibited.