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991.
G. Mulderij B. Mau L. N. de Senerpont Domis A. J. P. Smolders E. Van Donk 《Aquatic Ecology》2009,43(2):305-312
The aquatic macrophyte Stratiotes aloides Linnaeus, which has recently received attention in studies on allelopathy, has been shown to suppress phytoplankton growth.
In the Netherlands, S. aloides often co-occurs with floating filamentous algae. However, filamentous algae are generally absent in close proximity to S. aloides, resulting in gaps in filamentous algae mats. We analyzed whether those gaps may be caused by allelopathic substances excreted
by S. aloides or by nutrient depletion. We studied in a field survey the colonization of natural S. aloides by filamentous algae and determined in situ nutrient concentrations in natural S. aloides stands. To analyze the relative importance of allelopathy and nutrient competition in the interaction between S. aloides and filamentous algae, we carried out field experiments. Introduction of artificial (non-allelopathic) plants in natural
S. aloides stands enabled us to compare the colonization by filamentous algae of both Stratiotes sp. and artificial plants. The filamentous algae were absent in close vicinity to S. aloides. Significantly lower concentrations of ortho-phosphate and potassium were observed close to S. aloides as compared with the filamentous algae. In the field experiments the artificial plants were rapidly colonized by filamentous
algae, mainly Cladophera Kützing and Spirogyra Link, while all natural plants remained free of such algae. Additionally, most nutrient concentrations did not significantly
differ in the proximity of artificial or natural stands of S. aloides. The concentrations of the major growth-limiting nutrients, phosphate and nitrate, were significantly higher and nonlimiting
in natural Stratiotes stands. Our main conclusion is that, although allelopathic interactions between S. aloides and filamentous algae do occur under natural conditions, nutrient competition between the two can also be an important factor. 相似文献
992.
Haidong Ding Aying Zhang Jinxiang Wang Rui Lu Hong Zhang Jianhua Zhang Mingyi Jiang 《Planta》2009,230(2):239-251
Mitogen-activated protein kinase (MAPK) cascades have been shown to be important components in abscisic acid (ABA) signal
transduction pathway. In this study, a 46 kDa MAPK (p46MAPK) induced by ABA was partially purified from maize (Zea mays) by Q-Sepharose FF, Phenyl-Sepharose FF, Resource Q, Mono QTM 5/50 GL, poly-l-lysine-agarose, and Superdex 75 prep-grade columns, and was identified as ZmMAPK5 (gi|4239889) by the matrix-assisted laser
desorption/ionization time-of-flight/time-of-flight (MALDI-TOF/TOF) mass spectrometry. Furthermore, the kinase showed optimal
activity at pH 8.0, 30°C, and 10 mM MgCl2; the K
m
for myelin basic protein (MBP) substrate and ATP were 0.13 μg μl−1 and 62 μM, respectively. MBP was the preferred substrate, of which the threonine residue was phosphorylated. Finally, the
kinase was found to respond to diverse extracelluar stimuli. These results enable us to further reveal the function of the
ZmMAPK5 in ABA signaling.
The authors Haidong Ding and Aying Zhang contributed equally to the work. 相似文献
993.
994.
Lörinczi E Napp J Contreras-Jurado C Pardo LA Stühmer W 《European biophysics journal : EBJ》2009,38(3):279-284
The ether-à-go-go potassium channels hEag1 and hEag2 are highly homologous. Even though both possess identical voltage-sensing
domain S4, the channels act differently in response to voltage. Therefore we asked whether transmembrane domains other than
the voltage sensor could contribute to the voltage-dependent behaviour of these potassium channels. For this chimaeras were
created, in which each single transmembrane domain of hEag1 was replaced by the corresponding segment of hEag2. The voltage-dependent
properties of the chimaeras were analysed after expression in Xenopus laevis oocytes using the two-electrode voltage-clamp method. By this we found, that only the mutations in transmembrane domains
S5 and S6 are able to change the voltage sensitivity of hEag1 by shifting the half-activation potential (V
50) to values intermediate between the two wild types. Moreover, the presence of Mg2+ has strong effects on the voltage sensitivity of hEag2 shifting V
50 by more than 50 mV to more positive values. Interestingly, despite the identical binding site Mg2+ showed only little effects on hEag1 or the chimaeras. Altogether, our data suggest that not only transmembrane spanning regions,
but also non-membrane spanning regions are responsible for differences in the behaviour of the hEag1 and hEag2 potassium channels.
EBSA Satellite meeting: Ion channels, Leeds, July 2007. 相似文献
995.
Rym Zitari-Chatti Noureddine Chatti Domenico Fulgione Immacolata Caiazza Gennaro Aprea Ali Elouaer Khaled Said Teresa Capriglione 《Genetica》2009,136(3):439-447
In this study we analysed mitochondrial DNA variation in Penaeus kerathurus prawns collected from seven locations along a transect across the Siculo–Tunisian region in order to verify if any population
structuring exists over a limited geographical scale and to delineate the putative transition zone with sufficient accuracy.
Partial DNA sequences of COI and 16S genes were analysed. In contrast to the highly conservative 16S gene, the COI sequences
exhibited sufficient diversity for population analysis. The COI gene revealed low levels of haplotype and nucleotide diversities.
The size of the annual landings of this commercial species suggests large population sizes. Hence, the low genetic diversity
detected in this study could indicate a possible reduction in effective population sizes in the past. We detected significant
genetic differentiation between eastern and western populations likely due to restricted gene flow across the Siculo–Tunisian
boundary. We discuss the different evolutionary forces that may have shaped the genetic variation and suggest that the genetic
divide is probably maintained by present-day dispersal limitation.
R. Zitari-Chatti and N. Chatti are contributed equally to the work. 相似文献
996.
Diel variation of phytoplankton functional groups in a subtropical reservoir in southern Brazil during an autumnal stratification period 总被引:1,自引:0,他引:1
A knowledge of diel variation and the vertical distribution of phytoplankton communities may contribute to a better understanding
of the driving factors of key species. Applying functional-group classification provides important information on the causes
of species selection in the pelagic community. The diel variation of phytoplankton functional groups was analysed during an
autumnal stratification period with the aim of understanding their changes in the vertical position related to light, mixing
regime and grazing pressure. Phytoplankton and zooplankton communities were sampled every 4 h during a 24-h period in a vertical
profile in a subtropical meso-eutrophic reservoir. Strong stratification during a 24-h cycle and a mixed clear epilimnion
with partial atelomixis marked the autumn season in the Faxinal reservoir, southern Brazil. The highest phytoplankton densities
and biomass were found during the second part of the day, a general pattern reported in the literature, and may be explained
by zooplankton dynamics. During the 24-h cycle, phytoplankton functional groups lacking a self-regulating capacity and those
able to regulate their vertical position were vertically segregated in the lake. The diel behaviour of both groups was driven
by the mixing regime (including atelomixis), light and zooplankton grazing pressure. 相似文献
997.
Polyploidy, which is thought to have played an important role in plant evolution and speciation, is prevalent in Chrysanthemum (x = 9). In fact, polyploid series are known in C. zawadskii (2x, 4x, 6x, 8x, and 10x) and C. indicum (2x, 4x, and 6x), but the mechanism by which polyploidization occurs is unknown. Here we show that in diploid individuals of both C. zawadskii and C. indicum, the fusion between two adjacent pollen mother cells (PMCs) occurs at a frequency of 1.1–1.3% early in the first meiotic
division. While possessing the chromosomes of both PMCs, the fused cell or syncyte undertakes subsequent meiotic division
processes as a single large PMC, producing four 2n pollen grains that are able to germinate. Despite their low frequency, syncyte formation may have played a major role in
the production of infraspecific polyploids in Chrysanthemum. 相似文献
998.
Amanda Ferreira da Silva Mendes Luciana Cardoso Cidade Maria Luiza Peixoto de Oliveira Wagner Campos Otoni Walter Dos Santos Soares-Filho Marcio Gilberto Cardoso Costa 《Plant Cell, Tissue and Organ Culture》2009,97(3):331-336
Identification of beta-lactam antibiotics that have negligible effects on plant regeneration is a critical step towards the
establishment of a reliable Agrobacterium-mediated transformation protocol for perennial trees. In the present report, we have evaluated the effects of the novel beta-lactam
antibiotics meropenem and timentin on plant regeneration of a perennial woody fruit plant, Citrus sinensis, in comparison with the commonly used beta-lactam cefotaxime. It was observed that, in contrast to cefotaxime, meropenem
and timentin had a positive or no detrimental effect on the shoot regeneration from epicotyl explants. Residual effects of
the beta-lactams from shoot regeneration medium also affected the subsequent ability of the roots to elongate. The addition
of meropenem and/or timentin in the rooting medium mostly improved or did not affect the rooting ability of the adventitious
shoots. These data indicated that meropenem and timentin can positively replace cefotaxime in Agrobacterium-mediated transformation of C. sinensis. 相似文献
999.
Chris M. Wood Martin Grosell 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2009,179(4):459-467
Transepithelial potentials (TEP) were measured in killifish, acclimated to freshwater (FW), seawater (SW), 33% SW or cycling salinities relevant to tidal cycles in an estuary, and subsequently subjected to salinity changes in progressive
or random order. Random compared to progressive salinity changes in an upward or downward direction in FW- and SW-acclimated
fish, respectively, did not greatly influence responses to salinity change. Fish acclimated to SW or 33% SW as well as those
acclimated to cycling salinities behaved similarly (TEP more positive than +15 mV in 100% SW, decreasing to ~0 mV at 20–40%
SW, and more negative than −30 mV in FW). In contrast, FW-acclimated fish displayed a less pronounced TEP response to salinity
(0 mV in FW through 20% SW, increasing thereafter to values more positive than +10 mV at 100% SW). We conclude that when evaluated
under estuarine tidal conditions, the killifish gill exhibits adaptive electrical characteristics, opposing Na+ loss at low salinity and favouring Na+ extrusion at high salinity, changes explained at least in part by the Cl− to Na+ permeability ratio. Thus animals living in the estuaries can move to lower and higher salinities for short periods with little
physiological disturbance, but this ability is lost after acclimation to FW. 相似文献
1000.
Imran Sajid Clarisse Blandine Fotso Fondja Yao Khaled Attia Shaaban Shahida Hasnain Hartmut Laatsch 《World journal of microbiology & biotechnology》2009,25(4):601-610
A culture collection of 110 indigenous Streptomyces strains originally isolated from saline farmlands (Punjab, Pakistan) using stringent methods was screened biologically and
chemically to investigate their potential for the production of bioactive secondary metabolites. In a biological screening
the crude extracts obtained from the culture broth of selected strains were analysed for their activity against a set of test
organisms, including Gram-positive, Gram-negative bacteria, fungi and microalgae using the disk diffusion bioassay method.
Additionally a cytotoxicity test was performed by means of the brine shrimp microwell cytotoxicity assay. In a chemical screening
each of the crude extracts was analysed by TLC using various staining reagents and by HPLC-MS/MS measurements. The results
depicted an impressive chemical diversity of crude extracts produced by these strains. The taxonomic status of the selected
strains was confirmed by preliminary physiological testing and 16S rRNA gene sequencing. 相似文献