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81.
Nitrogen stable isotope ratios in surface sediments, epilithon and macrophytes from upland lakes with differing nutrient status 总被引:7,自引:0,他引:7
1. Thirty small upland lakes in Cumbria, Wales, Scotland and Northern Ireland were each visited once during June and July 2000. From each lake, samples of surface sediment epilithon, macrophytes and total dissolved nitrogen (TDN) were collected for nitrogen stable isotope analysis. As part of a wider programme, samples were also collected for chemical analysis and bioassays. 2. Considerable variation was found in δ15N values in all measured nitrogen compartments. Some regional variation was evident but was generally weak. Sediment and epilithon δ15N were positively correlated with δ15N of TDN, suggesting that baseline nitrogen isotope ratios influence those in some organic matter compartments in the lakes. 3. Sediment δ15N was higher when inorganic nitrogen concentration in the water was low, possibly reflecting reduced isotope fractionation under these conditions. However, this was not the case for epilithon or macrophytes. Sediment δ15N values were also negatively related to annual nitrogen deposition. 4. Sediment, epilithon and macrophyte δ15N values all showed significant relations to nutrient limitation in the lakes as determined by algal bioassays. We suggest that sediment δ15N might be developed as a simple integrating measure of the degree of nitrogen limitation in lakes. 相似文献
82.
J.M.R. Victor B.N.S. Murthy S.J. Murch S. KrishnaRaj P.K. Saxena 《Plant Growth Regulation》1999,28(1):41-47
Somatic embryogenesis was induced at the hypocotyledonary notch region of intact peanut (Arachis hypogaea L.) seedings cultured on a medium containing 10 mol·L–1 thidiazuron (TDZ). Inclusion of the purine analogs 2,6-diaminopurine (DAP), azaadenine or azaguanine to the thidiazuron amended medium inhibited the embryogenic response of the seedlings. DAP-mediated inhibition was not overcome by the addition of adenine sulphate. Inhibition of the embryogenic response by DAP provides evidence that the TDZ-induced accumulation of purine cytokinins is an essential component of TDZ-induced somatic embryogenesis process. Analyses of the endogenous level of purine metabolites indicated that supplementation of the media with TDZ resulted in an overall increase in the endogenous cytokinins while DAP inhibited the purine recycling resulting in decreased levels of endogenous adenine and zeatin. 相似文献
83.
Repp A Mikami K Mittmann F Hartmann E 《The Plant journal : for cell and molecular biology》2004,40(2):250-259
The phosphoinositide signalling pathway is important in plant responses to extracellular and intracellular signals. To elucidate the physiological functions of phosphoinositide-specific phopspholipase C, PI-PLC, targeted knockout mutants of PpPLC1, a gene encoding a PI-PLC from the moss Physcomitrella patens, were generated via homologous recombination. Protonemal filaments of the plc1 lines show a dramatic reduction in gametophore formation relative to wild type: this was accompanied by a loss of sensitivity to cytokinin. Moreover, plc1 appeared paler than the wild type, the result of an altered differentiation of chloroplasts and reduced chlorophyll levels compared with wild type filaments. In addition, the protonemal filaments of plc1 have a strongly reduced ability to grow negatively gravitropically in the dark. These effects imply a significant role for PpPLC1 in cytokinin signalling and gravitropism. 相似文献
84.
Two-component systems have emerged as important sensing/response mechanisms in higher plants. They are composed of hybrid histidine kinases, histidine-containing phosphotransfer domain proteins and response regulators that are biochemically linked by His-to-Asp phosphorelay. In plants two-component systems play a major role in cytokinin perception and signalling and contribute to ethylene signal transduction and osmosensing. Furthermore, developmental processes like megagametogenesis in Arabidopsis thaliana and flowering promotion in rice (Oryza sativa) involve elements of two-component systems. Two-component-like elements also function as components of the Arabidopsis circadian clock. Because of the molecular mode of signalling, plant two-component systems also appear to serve as intensive cross talk and signal integration machinery. In this review we summarize the present knowledge about the principles and functions of two-component systems in higher plants and address several critical points with respect to cross talk, signal integration and specificity.Abbreviations AHK Arabidopsis histidine kinase - AHP Arabidopsis histidine-containing phosphotransfer domain protein - APRR Arabidopsis pseudo response regulator - ARR Arabidopsis response regulator - CCT CONSTANS CONSTANS-like TOC1 - CKI Cytokinin insensitive - CRE Cytokinin response - CTR Constitutive triple response - Ehd Early heading date - EIN Ethylene insensitive - ERS Ethylene response sensor - ETR Ethylene resistant - GARP-motif Found in Golden2 of maize, Arabidopsis B-type response regulators and Chlamydomonas Psr1 - HPt Histidine-containing phosphotransfer domain - NLS Nuclear localization signal - phyB Phytochrome B - TCS Two-component signalling - TOC Timing of CAB (chlorophyll a/b-binding protein) expression - WOL Wooden leg 相似文献
85.
Maruyama-Nakashita A Nakamura Y Yamaya T Takahashi H 《The Plant journal : for cell and molecular biology》2004,38(5):779-789
Cytokinin is an adenine derivative plant hormone that generally regulates plant cell division and differentiation in conjunction with auxin. We report that a major cue for the negative regulation of sulfur acquisition is executed by cytokinin response 1 (CRE1)/wooden leg (WOL)/Arabidopsis histidine kinase 4 (AHK4) cytokinin receptor in Arabidopsis root. We constructed a green fluorescent protein (GFP) reporter system that generally displays the expression of the high-affinity sulfate transporter SULTR1;2 in Arabidopsis roots. GFP under the control of SULTR1;2 promoter showed typical sulfur responses that correlate with the changes in SULTR1;2 mRNA levels; accumulation of GFP was induced by sulfur limitation (-S), but was repressed in the presence of reduced sulfur compounds. Among the plant hormones tested, cytokinin significantly downregulated the expression of SULTR1;2. SULTR1;1 conducting sulfate uptake in sultr1;2 mutant was similarly downregulated by cytokinin. Downregulation of SULTR1;1 and SULTR1;2 by cytokinin correlated with the decrease in sulfate uptake activities in roots. The effect of cytokinin on sulfate uptake was moderated in the cre1-1 mutant, providing genetic evidence for involvement of CRE1/WOL/AHK4 in the negative regulation of high-affinity sulfate transporters. These data demonstrated the physiological importance of the cytokinin-dependent regulatory pathway in acquisition of sulfate in roots. Our results suggested that two different modes of regulation, represented as the -S induction and the cytokinin-dependent repression of sulfate transporters, independently control the uptake of sulfate in Arabidopsis roots. 相似文献
86.
Adams KJ Chavasse DC Mount DL Carneiro IA Curtis CF 《Medical and veterinary entomology》2002,16(1):106-108
Adult mosquitoes, Anopheles gambiae Giles and Culex quinquefasciatus Say (Diptera: Culicidae), were exposed for 3 min to replicate samples of polyester netting cut from replicate bednets treated with pyrethroid insecticide formulations at the recommended concentration (alphacypermethrin SC at 40mg ai/m2; cyfluthrin EW at 50 mg ai/m2; deltamethrin WT at 25 mg ai/m2), or treated with only a quarter of those dosages. After 4 months domestic use of the bednets in Malawi, chemical assays showed that pyrethroid deposits on the netting were somewhat less than the target concentrations. Comparing the pyrethroid bioassay results with Anopheles at both treatment concentrations, deltamethrin gave significantly higher mortality (99.7-100%) than the other compounds (alphacypermethrin 94-96%, cyfluthrin 80-89%). Culex bioassay mortality was lower (alphacypermethrin 56-74%; cyfluthrin 63-65%; deltamethrin 50-81 %) and results with the three pyrethroid insecticides at their recommended doses did not differ significantly. 相似文献
87.
Summary Cell cultures of freshwater wetland monocots were regenerated, plants were grown in the greenhouse, and then established and
evaluated in wetlands. Typha (cattail), Juncus (rushes), Scirpus (bulrushes), and Carex (sedges) were studied because they are common, dominant, high biomass wetland-adapted plants, tolerant of chemically diverse
ecosystems. The goal was to define micropropagation and wetland establishment protocols. Tissue culture systems defined for
numerous monocot crop species can be readily applied to wetland plants, with a few modifications. Issues addressed were selection
of explant material, shoot and root regeneration conditions, culture age verses regenerability, greenhouse acclimatization
needs, plant uniformity and requirements for wetland establishment. In vitro-germinated seedlings were an excellent source of pathogen-free regenerable tissue. T. latifolia, T. angustifolia, and J. accuminatus were regenerated from callus induced in the dark with picloram, then transferred to medium with benzyladenine in the light
to promote shoot organogenesis. J. effusus, S. polyphyllus, and C. lurida could not be regenerated from callus, which turned black. They could be regenerated directly by culturing intact seedlings
directly on cytokinin media in the light. Shoots rooted with little or no auxin. J. effusus rooting was promoted by the addition of charcoal to the medium. Covering plants for the first 2 wk with plastic facilitated
greenhouse establishment. There were high rates of greenhouse and wetland survival. No abnormal plants were observed. These
regeneration systems could be utilized for the production of wetland plants for potential application in habitat restoration
and wetland creation, and would provide an alternative to field collection. 相似文献
88.
We isolated Arabidopsis thaliana mutants that respond more sensitively than the wild type to cytokinins. The calli produced from the mutants exhibit typical cytokinin responses, including rapid proliferation and chloroplast development in response to lower levels of cytokinins than in the wild type. The mutations are recessive and belong to two complementation groups designated ckh1 and ckh2 for cytokinin-hypersensitive. CKH1 and CKH2 were mapped to the top of chromosome I and the middle of chromosome II, respectively. The cytokinin levels in these mutants were not increased. We speculate that the CKH1 and CKH2 gene products negatively regulate the signaling pathway leading from cytokinin perception to cell proliferation and chloroplast development. 相似文献
89.
Guillaume Tetreau Renaud Stalinski Jean-Philippe David Laurence Després 《Memórias do Instituto Oswaldo Cruz》2013,108(7):894-900
Bacillus thuringiensis subsp. israelensis (Bti) is increasingly used worldwide for mosquito control and is the only larvicide used in the French Rhône-Alpes region since decades. The artificial selection of mosquitoes with field-persistent Bti collected in breeding sites from this region led to a moderate level of resistance to Bti, but to relatively high levels of resistance to individual Bti Cry toxins. Based on this observation, we developed a bioassay procedure using each Bti Cry toxin separately to detect cryptic Bti-resistance evolving in field mosquito populations. Although no resistance to Bti was detected in none of the three mosquito species tested (Aedes rusticus, Aedes sticticus and Aedes vexans), an increased tolerance to Cry4Aa (3.5-fold) and Cry11Aa toxins (8-fold) was found in one Ae. sticticus population compared to other populations of the same species, suggesting that resistance to Bti may be arising in this population. This study confirms previous works showing a lack of Bti resistance in field mosquito populations treated for decades with this bioinsecticide. It also provides a first panorama of their susceptibility status to individual Bti Cry toxins. In combination with bioassays with Bti, bioassays with separate Cry toxins allow a more sensitive monitoring of Bti-resistance in the field. 相似文献
90.
Jaren?I.?Madden Cynthia?S.?JonesEmail author Carol?A.?Auer 《In vitro cellular & developmental biology. Plant》2005,41(1):37-46
Summary Modes of regeneration from hypocotyl explants were studied in Pelargonium × hortorum ‘Scarlet Orbit,’ and three wild relatives, P. zonale, P. alchemilloides, and P. inquinans, on different cytokinin treatments [1 μM thidiazuron (TDZ), 4 μM TDZ, or 8 μM N6-benzylaminopurine (BA) and 1 μM indole-3-acetic acid (IAA)]. P. × hortorum ‘Scarlet Orbit’ and P. zonale showed similar high numbers of easily detached, embryo-like structures in response to 1 μM TDZ; P. alchemilloides and P. inquinans showed weak embryogenic responses to all treatments. To revisit whether P. × hortorum produces somatic embryos, and to examine modes of regeneration in the wild species, the histology of regenerating structures
on hypocotyl explants in 1 μM TDZ was examined. Both P. × hortorum and P. zonale produced embryo-like structures from single cell derivatives of epidermal cells. Globular-shaped structures transitioned
into heart-shaped structures that had loose attachments to explant surfaces and no vascular connection to the explant. Roots
with direct vascular connections to the rest of the embryo-like structures were never observed; root organogenesis appeared
to be secondary. We propose that P. × hortorum and P. zonale exhibit partial somatic embryogenesis, in which all of the criteria for somatic embryos are met except formation of a root
pole. In both species, explants forming embryo-like structures could also undergo shoot organogenesis, where shoots exhibited
a broad base of attachment to the explant and a vascular connection to vascular nodules within the explant. Epidermally derived
embryo-like structures were not observed in P. alchemilloides or P. inquinans in response to 1 μM TDZ. Shoot organogenesis occurred in P. alchemilloides but not in P. inquinans. 相似文献