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161.
162.
163.
We compared various aspects of the seed biology of eight non-pioneer tree species from a tropical seasonal rain forest in
Xishuangbanna, SW China, that differ in time of dispersal, size and fresh seed moisture content (MC). Seeds were tested for
germination under laboratory conditions after dehydration to different moisture levels and under 3.5, 10 and 30% solar irradiances
in neutral-shade houses. For six species, germination was also compared in forest understory (3.5% light) and center of a
forest gap (32.5% light). Under continuous dehydration over activated silica gel, 100% of seeds of four species had lost the
ability to germinate after 48 h, and those of all species except Castanopsis hystrix (decreased from >90 to 30% germination) had lost the ability to germinate after 120 h. Four species did not differ in final
germination percentages at the three irradiances (i.e. uniform germination). However, final germination percentages of Horsfieldia pandurifolia and Litsea pierrei var. szemaois were significantly lower in 30% than in 10 or 3.5% light, and seeds of Antiaris toxicaria and C. hystrix germinated to higher percentages in 30 and 10% than in 3.5% light. Mean time to germination (MTG) of the eight species (forest
and shade house data combined) ranged from 5–5 days for Pometia
tomentosa to 72–207days for L. pierrei; MTG for four species was ≤21 days. There was no obvious relationship between relative desiccation resistance and either
time of dispersal, MTG or uniformity of germination at the three light levels, or between seed size and MC or MTG. However,
the relationship between seed MC at maturity (25–60% fresh mass basis) and MC at 50% loss of seed viability (12.4–42.5%) was
significant. Seven of the species fit Garwood’s (Ecol Monogr 53:159–181, 1983) rapid-rainy germination syndrome and one, L. pierrei, either her delayed-rainy or intermediate-dry germination syndrome. However, fresh, non-dehydrated seeds of all eight species
germinated in ≤30 days at constant 30°C in light. 相似文献
164.
Ferrous Iron Stimulates Phenol Oxidase Activity and Organic Matter Decomposition in Waterlogged Wetlands 总被引:1,自引:0,他引:1
Peter?M.?Van?BodegomEmail author Rob?Broekman Jerry?Van?Dijk Chris?Bakker Rien?Aerts 《Biogeochemistry》2005,76(1):69-83
Soil organic matter decomposition is limited at waterlogged conditions by the low activity of extracellular enzymes like phenol
oxidases. In this paper, we show that ferrous iron (Fe2+), which is abundant in waterlogged soils, significantly stimulates phenol oxidase activity both in pure enzyme assays and
in waterlogged soil slurries from nutrient-poor dune slacks. However, the effects in soil slurries were less strong than in
enzyme assays. Both the addition of Fe2+ and the initial presence of Fe2+ stimulated phenol oxidase activity at the microaerophilic conditions tested. This stimulation is attributed to the catalysis
of additional OH radical production, promoting the oxidation of phenolics. Subsequently, the presence of Fe2+ strongly increased total decomposition rates of soil organic matter, measured as CO2 production and Cotton strip Tensile Strength Loss. There is circumstantial evidence that this stimulation by Fe2+ could be important for decomposition in wetlands at field conditions, but its relevance compared to the effects of other
compounds still needs to be elucidated. These results emphasise the crucial role of water quality in determining extracellular
enzyme activity and decomposition in waterlogged wetlands. 相似文献
165.
Dobrian AD Lieb DC Cole BK Taylor-Fishwick DA Chakrabarti SK Nadler JL 《Progress in lipid research》2011,50(1):115-131
The 12/15-lipoxygenase enzymes react with fatty acids producing active lipid metabolites that are involved in a number of significant disease states. The latter include type 1 and type 2 diabetes (and associated complications), cardiovascular disease, hypertension, renal disease, and the neurological conditions Alzheimer’s disease and Parkinson’s disease. A number of elegant studies over the last thirty years have contributed to unraveling the role that lipoxygenases play in chronic inflammation. The development of animal models with targeted gene deletions has led to a better understanding of the role that lipoxygenases play in various conditions. Selective inhibitors of the different lipoxygenase isoforms are an active area of investigation, and will be both an important research tool and a promising therapeutic target for treating a wide spectrum of human diseases. 相似文献
166.
Staron RS Kraemer WJ Hikida RS Fry AC Murray JD Campos GE 《Histochemistry and cell biology》1999,111(2):117-123
The limb and trunk muscles of adult rats express four myosin heavy chain (MHC) isoforms, one slow (MHCI) and three fast (MHCIIa,
MHCIId, and MHCIIb). The distribution of these isoforms correlates with fiber types delineated using myofibrillar actomyosin
adenosine triphosphatase (mATPase) histochemistry. For example, type I fibers express MHCI and fiber types IIA, IID, and IIB
express MHCIIa, MHCIId, and MHCIIb, respectively. Fibers containing only one MHC isoform have been termed ”pure” fibers. Recent
evidence suggests that a population of ”hybrid” fibers exist in rat skeletal muscle which contain two MHC isoforms. The purpose
of the present investigation was to document the entire range of histochemically defined ”pure” and ”hybrid” fiber types in
untreated muscles of the young adult Fisher 344 rat hindlimb. The selected hindlimb muscles (soleus, tibialis anterior, extensor
digitorum longus, and gastrocnemius muscles) were removed from 12 male rats and analyzed for muscle fiber type distribution,
cross-sectional area, and MHC content. Care was taken to delineate eight fiber types (I, IC, IIC, IIA, IIAD, IID, IIDB, and
IIB) using refined histochemical techniques. Hybrid fibers were found to make up a considerable portion of the muscles examined
(a range of 8.8–17.8% of the total). The deep red portion of the gastrocnemius muscle contained the largest number of hybrid
fibers, most of which were the fast types IIAD (8.5±2.8%) and IIDB (5.2±2.3%). In conclusion, hybrid fibers make up a considerable
portion of normal rat limb musculature and are an important population that should not be ignored.
Accepted: 15 October 1998 相似文献
167.
Proapoptotic BH3-only Bcl-2 family member Bik/Blk/Nbk is expressed in hemopoietic and endothelial cells but is redundant for their programmed death 下载免费PDF全文
Coultas L Bouillet P Stanley EG Brodnicki TC Adams JM Strasser A 《Molecular and cellular biology》2004,24(4):1570-1581
The BH3-only members of the Bcl-2 protein family are essential for initiation of programmed cell death and stress-induced apoptosis. We have determined the expression pattern in mice of the BH3-only protein Bik, also called Blk or Nbk, and examined its physiological function by gene targeting. We found that Bik is expressed widely in the hematopoietic compartment and in endothelial cells of the venous but not arterial lineages. Nevertheless, its loss did not increase the numbers of such cells in mice or protect hematopoietic cells in vitro from apoptosis induced by cytokine withdrawal or diverse other cytotoxic stimuli. Moreover, whereas loss of the BH3-only protein Bim rescued mice lacking the prosurvival protein Bcl-2 from fatal polycystic kidney disease and lymphopenia, loss of Bik did not. These results indicate that any function of Bik in programmed cell death and stress-induced apoptosis must overlap that of other BH3-only proteins. 相似文献
168.
Nishi H Nakada T Kyo S Inoue M Shay JW Isaka K 《Molecular and cellular biology》2004,24(13):6076-6083
Hypoxia occurs during the development of the placenta in the first trimester and correlates with both trophoblast differentiation and the induction of telomerase activity through hTERT expression. We sought to determine the mechanism of regulation of hTERT expression during hypoxia. We show that hypoxia-inducible factor 1alpha (HIF-1alpha) and hTERT expression in the human placenta decrease with gestational age and that these are overexpressed in preeclamptic placenta, a major complication of pregnancy. Hypoxia not only transactivates the hTERT promoter activity but also enhances endogenous hTERT expression. The hTERT promoter region between -165 and +51 contains two HIF-1 consensus motifs, and in vitro reporter assays show that these are essential for hTERT transactivation by HIF-1. Introduction of an antisense oligonucleotide for HIF-1 diminishes hTERT expression during hypoxia, indicating that upregulation of hTERT by hypoxia is directly mediated through HIF-1. Our results provide persuasive evidence that the regulation of hTERT promoter activity by HIF-1 represents a mechanism for trophoblast growth during hypoxia and suggests that this may be a generalized response to hypoxia in various human disorders including resistance to cancer therapeutics by upregulating telomerase. 相似文献
169.
Dagkessamanskaia A Moscoso M Hénard V Guiral S Overweg K Reuter M Martin B Wells J Claverys JP 《Molecular microbiology》2004,51(4):1071-1086
170.
Conservation of fragmented small populations: endemic species persistence on California's smallest channel island 总被引:1,自引:1,他引:0
We examined resilience to extreme reduction of habitat, and long-term and long-distance isolation for an endemic species using California's Santa Barbara Island as a natural model. The island is smaller than 260ha, has been isolated by 40km of ocean from the nearest other island for more than 10,000 years and was severely impacted by human activities and feral browsers during at least the past 90 years. Less than 0.2km2 of native plant cover remains, yet seven apparently endemic plants and animals persist, including a moth, Argyrotaenia isolatissima (Tortricidae). Using mitochondrial DNA sequence we examined the levels of genetic divergence between the moth and its closest relatives on the other Channel Islands and the California mainland. A. isolatissima has 15bp differences, including one non-synonymous substitution, from the most closely related taxon, on San Nicolas Island. Both parsimony and likelihood-based molecular systematic analyses confirm the evolutionary independence of A. isolatissima and indicate that portions of an endemic flora and fauna may persist in small fragments, despite long-term isolation and disturbance. Habitat conservation planning may underestimate the value of very small, temporally and spatially isolated fragments of native habitat not only to maintain, but also to generate endemic biodiversity. 相似文献