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1.
The release from dormancy of Euonvmus europaeus L embryos bya brief treatment with GA3 has been studied During 48 h incubationof dormant embryos in GA-free medium, phospholipid levels increasedat first, then declined sharply over the last 6 h When the embryoswere placed in GA3 medium during this 6 h period levels of totalphospholipids as well as of phosphatidylethanolamine increasedwhilst phosphatidylinositol and phosphatidylcholine declinedslightly Fine structural changes stimulated by a brief GA3 treatmentwere of different character depending on tissue region (1) destructivechanges occurred in the superficial procortical parenchyma onthe hypocotyl/radicle boundary, involving autolysis and decompartmentationof organelles, (2) positive changes occurred inregions close to root and shoot apical meristems, involvingdegradation of protein bodies and their conversion into vacuoles,and the proliferation of various organelles A number of differenceswere noted when the changes in GA3-treated embryos were comparedwith those induced by low temperature, which also overcomesdormancy The results suggest that germination is accompaniedby different cytological events depending on whether it is inducedby cold or GA3 The growth of embryos in which dormancy was overcomeby GA3 was due to the activation of the apical root meristemclose to the quiescent centre, whilst in embryos in which germinationwas induced by low temperature, the periphery of hypotocotyl/radicleboundary was the site of activation Euonymus europaeus L, dormant embryo, fine structure, phospholipids, GA3 and cold treatments 相似文献
2.
LAURE LECOIN PASCALE MERCIER NICOLE M. LE DOUARIN 《Pigment cell & melanoma research》1994,7(4):210-216
In the Silky Fowl (SF) breed of chicken, most of the internal organs are infiltrated with melanocytes. Previous studies have shown that this generalized mesodermal pigmentation is not due to a cell autonomous abnormality of the melanocytes but to environmental factors able to promote both the homing of pigment cell precursors in abnormal embryonic sites and their proliferation and differentiation. To analyse the mode of these environmental cues, we tested the effect of SF embryo extract (SFEE) on cultured quail neural crest cells as compared with that of EE from normal chickens of the JA57 strain (JA57EE). We found that SFEE enhances crest cell proliferation as judged by 3H-TdR incorporation and cell counting. In contrast, no effect of SFEE was observed either on the proportion of cultured cells that are engaged into the melanocytic differentiation pathway or on the amount of melanin produced by each differentiated pigment cell. The simple observation, however, reveals that SFEE has a significant effect on pigmentation of the cultured quail neural crest cells. This effect has therefore to be accounted for by the general increase in cell number induced by SFEE. The question is raised as to whether the in vivo SF phenotype is generated exclusively by this mechanism. 相似文献
3.
Slow response of soil organic matter to the reduction in atmospheric nitrogen deposition in a Norway spruce forest 总被引:1,自引:0,他引:1
NICOLE DÖRR KLAUS KAISER ROBERT MIKUTTA GEORG GUGGENBERGER 《Global Change Biology》2010,16(11):2990-3003
Global nitrogen (N) deposition rates in terrestrial environments have quadrupled since preindustrial times, causing structural and functional changes of ecosystems. Different emission reduction policies were therefore devised. The aim of our study was to investigate if, and over what timescale, processes of soil organic matter (OM) transformation respond to a decline in atmospheric N deposition. A N‐saturated spruce forest (current N deposition: 34 kg ha?1 yr?1; critical N load: 14 kg ha?1 yr?1), where N deposition has been reduced to 11.5 kg ha?1 yr?1 since 1991, was studied. Besides organic C and organic and inorganic N, noncellulosic carbohydrates, amino sugars and amino acids were determined. A decline in organic N in litter indicated initial effects at plant level. However, there were no changes in biomarkers upon the reduction in N deposition. In addition, inorganic N was not affected by reduced N deposition. The results showed that OM cycling and transformation processes have not responded so far. It was concluded that no direct N deposition effects have occurred due to the large amount of stored organic N, which seems to compensate for the reduction in deposited N. Obviously, the time span of atmospheric N reduction (about 14.5 years) is too short compared with the mean turnover time of litter to cause indirect effects on the composition of organic C and N compounds. It is assumed that ecological processes, such as microbial decomposition or recycling of organic N and C, react slowly, but may start within the next decade with the incorporation of the new litter. 相似文献
4.
NICOLE ANDRIEUX J. DE FRESCHEVILLE JOSETTE BERREUR-BONNENFANT 《Invertebrate reproduction & development.》2013,57(1-3):87-93
Summary We have analysed in vitro the effect of farnesylacetone, a substance produced by the androgenic gland of Crustacea, in a concentration of 20 ng/ml, on the protein synthesis in the ovary of Carcinus maenas. In winter, the farneslyacetone seems to be ineffective; the incorporation of labelled precursor per mass unity is then related to the weight of the sample. In summer, an activation of protein synthesis can be observed. These results do not depend on ovary maturation and concern all the proteins of the gonad. 相似文献
5.
ERIK H. POELMAN JOOP J. A. VAN LOON NICOLE M. VAN DAM LOUISE E. M. VET MARCEL DICKE 《Ecological Entomology》2010,35(2):240-247
1. Plant responses to herbivore attack may have community‐wide effects on the composition of the plant‐associated insect community. Thereby, plant responses to an early‐season herbivore may have profound consequences for the amount and type of future attack. 2. Here we studied the effect of early‐season herbivory by caterpillars of Pieris rapae on the composition of the insect herbivore community on domesticated Brassica oleracea plants. We compared the effect of herbivory on two cultivars that differ in the degree of susceptibility to herbivores to analyse whether induced plant responses supersede differences caused by constitutive resistance. 3. Early‐season herbivory affected the herbivore community, having contrasting effects on different herbivore species, while these effects were similar on the two cultivars. Generalist insect herbivores avoided plants that had been induced, whereas these plants were colonised preferentially by specialist herbivores belonging to both leaf‐chewing and sap‐sucking guilds. 4. Our results show that community‐wide effects of early‐season herbivory may prevail over effects of constitutive plant resistance. Induced responses triggered by prior herbivory may lead to an increase in susceptibility to the dominant specialists in the herbivorous insect community. The outcome of the balance between contrasting responses of herbivorous community members to induced plants therefore determines whether induced plant responses result in enhanced plant resistance. 相似文献
6.
SONIA M. HERNANDEZ DANIEL J. GAMMONS NICOLE GOTTDENKER MICHAEL T. MENGAK L. MIKE CONNER STEPHEN J. DIVERS 《The Journal of wildlife management》2010,74(1):174-180
ABSTRACT The future management of nine-banded armadillos (Dasypus novemcinctus) requires solid space-use and activity data, which are currently lacking and which radiotelemetry can provide. External radiotransmitters have not been successful applied with this species. To make recommendations for intra-abdominal radiotransmitter placement in nine-banded armadillos, we 1) evaluated 4 different anesthetic protocols for safety, efficiency, and cost-effectiveness; 2) evaluated a surgical technique for the intra-abdominal placement of radiotransmitters that addresses problems described in previous studies; and 3) evaluated the physiologic and behavioral effects of such a technique. We captured and surgically implanted 37 nine-banded armadillos using either butorphanol and isoflurane, ketamine alone, ketamine and xylazine, or a combination of butorphanol, ketamine, and medetomidine for anesthesia. We recovered and necropsied armadillos after the completion of the study. The objective and subjective assessment of butorphanol, ketamine, and medetomidine combination protocol, followed by reversal of the anesthesia with atipamezole, showed that it was the best overall anesthetic protocol for field use, providing both a smooth induction and fast recovery. We evaluated the fate and effects of radiotransmitters on 13 recovered animals at the end of the study and found no adverse effects. We recommend the implantation of radiotransmitters that are allowed to free-float within the abdominal cavity and specifically emphasize the need for strict aseptic technique. Wildlife managers and wildlife veterinarians aiming to implant nine-banded armadillos with radiotransmitters will benefit from using the recommended anesthetic protocol and surgical technique in future studies. 相似文献
7.
Abstract: A major challenge facing wildlife biologists is understanding why some species go extinct while others persist in the same habitat. To address this question, we investigated whether tree canopy closure over ponds affects growth and survival of rare and common tadpoles within ponds and mediates competitive interactions among species. We conducted 2 experiments to test whether canopy closure and competition may have contributed to the decline of the endangered dusky gopher frog (Rana sevosa), but allowed the persistence of the southern leopard frog (R. sphenocephala). We explored the response of both species to canopy closure in single-species and mixed- (1:1) species treatments of identical total tadpole density. An experiment using aquatic enclosures in temporary ponds showed that canopy closure reduced tadpole growth approximately 20% for both species. Survival of dusky gopher frog tadpoles was higher in mixed-species enclosures than in single-species enclosures. In a complementary experiment using artificial ponds, dusky gopher frogs had lower survival to metamorphosis, reduced size at metamorphosis, and produced a lower total biomass of metamorphosed juveniles in shaded ponds. Southern leopard frogs exhibited reduced body size at metamorphosis only when shaded. These studies suggest that pond canopy closure, not larval competition, may be contributing to the decline of the dusky gopher frog. The different responses to canopy closure suggest a potential mechanism for the loss of dusky gopher frogs and the persistence of southern leopard frogs. Removal of trees from historically open-canopy ponds may help facilitate the recovery of dusky gopher frogs and benefit similar species. 相似文献
8.
CHRISTOPHER J. KATZ SCOTT C. ANDERSON ROBERT W. HOWE ANDREW R. HINICKLE NICOLE T. WALISZEWSKI STACY A. NYE AARON M. WUNDERLIN 《The Journal of wildlife management》2007,71(2):634-636
ABSTRACT Knowledge of the distribution and pathology of West Nile virus (WNV) in black bears is a necessary tool that allows wildlife managers to implement a management plan, set harvest quotas, and relocate nuisance bears. We studied the presence and significance of WNV titers in free-roaming black bears (Ursus americanus) in northeastern Wisconsin between February 2003 and March 2005. Serum neutralizing antibodies to WNV, with confirmation by plaque-reduction neutralization test to both WNV and Saint Louis encephalitis, identified exposure in 13 of 74 (17.6%) bears. This compares with a 6% infection rate in black bears in Virginia and 22% in European brown bears (Ursus arctos). Pathologic effects from exposure to WNV were not seen in any of the black bears studied. 相似文献
9.
DUBILIER NICOLE; GIERE OLAV; GRIESHABER MANFRED K. 《Integrative and comparative biology》1995,35(2):163-173
SYNOPSIS. The marine oligochaete worm Tubificoides benedii inhabitscoastal tidal sediments in which sulfide can reach toxic concentrations.The role of external ironsulfide deposition in sulfide detoxificationis discussed together with a review of morphological and ecophysiologicaladaptations of T. benedii to sulfide. The body wall of T. benediiturns black in the presence of sulfide. Histochemical studiesand micro-X-rayanalyses provide evidence for the reaction ofiron in the mucus layer above the cuticle of the worm with environmentalsulfide to produce ironsulfide. The deposited ironsulfides areeither reoxidized or shed off through moulting, a process otherwiseunknown in oligochaetes. However, calculations on the diffusionrate of sulfide into T. benedii show that the deposition ofironsulfides do not play an important role in sulfide detoxification.The first and last few segments of T. benedii are not blackenedby sulfide and do not appear to precipitate sulfide. The diffusionrate of sulfide through these segments is so rapid that internalsulfide concentrations reach levels inhibitory to cytochromec oxidase, the key enzyme of aerobic respiration, within minutes.When internal sulfide concentrations increase to toxic levels,reliance on an anaerobic metabolism represents a successfulmechanism of sulfide tolerance in T. benedii. Metabolic adaptationsto hypoxia and sulfide include the maintenance of aerobic pathwaysdespite low oxygen or high sulfide concentrations and the abilityto gain energy through anaerobic pathways when oxygen and/orsulfide concentrations become limiting 相似文献
10.
ANASTASIA TSAGKARAKOU MARIA NAVAJAS PAGONA PAPAIOANNOU-SOULIOTIS & NICOLE PASTEUR† 《Molecular ecology》1998,7(1):71-79
Polymorphism of four enzymatic loci has been examined in 27 populations of Tetranychus urticae in relation to their geographical distribution and to two ecological parameters: open field vs. greenhouse habitats, and species of the colonized host plant. Genetic differentiation was significantly correlated to geographical distance in both types of habitat. Mite density and distribution of infested plants appear to be important factors for the population structure of T. urticae . In open field, T. urticae specimens from citrus trees were genetically more similar to other 'citrus' samples collected in different localities than they were from mites collected in the same locality on other plant species. 相似文献